1
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Xu P, Liu H, Liu C, Zhu G. Syntrophic methane production from volatile fatty acids: Focus on interspecies electron transfer. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 946:174410. [PMID: 38960157 DOI: 10.1016/j.scitotenv.2024.174410] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/22/2024] [Revised: 06/28/2024] [Accepted: 06/29/2024] [Indexed: 07/05/2024]
Abstract
Methane is a renewable biomass energy source produced via anaerobic digestion (AD). Interspecies electron transfer (IET) between methanogens and syntrophic bacteria is crucial for mitigating energy barriers in this process. Understanding IET is essential for enhancing the efficiency of syntrophic methanogenesis in anaerobic digestion. Interspecies electron transfer mechanisms include interspecies H2/formate transfer, direct interspecies electron transfer (DIET), and electron-shuttle-mediated transfer. This review summarizes the mechanisms, developments, and research gaps in IET pathways. Interspecies H2/formate transfer requires strict control of low H2 partial pressure and involves complex enzymatic reactions. In contrast, DIET enhances the electron transfer efficiency and process stability. Conductive materials and key microorganisms can be modulated to stimulate the DIET. Electron shuttles (ES) allow microorganisms to interact with extracellular electron acceptors without direct contact; however, their efficiency depends on various factors. Future studies should elucidate the key functional groups, metabolic pathways, and regulatory mechanisms of IET to guide the optimization of AD processes for efficient renewable energy production.
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Affiliation(s)
- Panhui Xu
- School of Chemistry and Life Resources, Renmin University of China, Beijing 100872, China
| | - Haichen Liu
- Shanghai Investigation, Design & Research Institute Co., Ltd., 200080, China
| | - Chong Liu
- The 101 Research Institute, Ministry of Civil Affairs of the People's Republic of China, Beijing 100070, China.
| | - Gefu Zhu
- School of Chemistry and Life Resources, Renmin University of China, Beijing 100872, China
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2
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Chen X, Yang G, Quan X, Zhu S, Qin B, Shou D, Zhuang L. Significance of a minor pilin PilV in biofilm cohesion of Geobacter sulfurreducens. THE SCIENCE OF THE TOTAL ENVIRONMENT 2024; 927:172242. [PMID: 38582122 DOI: 10.1016/j.scitotenv.2024.172242] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/14/2023] [Revised: 04/03/2024] [Accepted: 04/03/2024] [Indexed: 04/08/2024]
Abstract
Bacterial adhesion plays a vital role in forming and shaping the structure of electroactive biofilms that are essential for the performance of bioelectrochemical systems (BESs). Type IV pili are known to mediate cell adhesion in many Gram-negative bacteria, but the mechanism of pili-mediated cell adhesion of Geobacter species on anode surface remains unclear. Herein, a minor pilin PilV2 was found to be essential for cell adhesion ability of Geobacter sulfurreducens since the lack of pilV2 gene depressed the cell adhesion capability by 81.2% in microplate and the anodic biofilm density by 23.1 % at -0.1 V and 37.7 % at -0.3 V in BESs. The less cohesiveness of mutant biofilms increased the charge transfer resistance and biofilm resistance, which correspondingly lowered current generation of the pilV2-deficient strain by up to 63.2 % compared with that of the wild-type strain in BESs. The deletion of pilV2 posed an insignificant effect on the production of extracellular polysaccharides, pili, extracellular cytochromes and electron shuttles that are involved in biofilm formation or extracellular electron transfer (EET) process. This study demonstrated the significance of pilV2 gene in cell adhesion and biofilm formation of G. sulfurreducens, as well as the importance of pili-mediated adhesion for EET of electroactive biofilm.
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Affiliation(s)
- Xiaochun Chen
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Guiqin Yang
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Xiaoyun Quan
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Siyue Zhu
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Baoli Qin
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Danyang Shou
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Li Zhuang
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China.
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3
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Schwarz IA, Alsaqri B, Lekbach Y, Henry K, Gorman S, Woodard T, Dion L, Real L, Holmes DE, Smith JA, Lovley DR. Lack of physiological evidence for cytochrome filaments functioning as conduits for extracellular electron transfer. mBio 2024; 15:e0069024. [PMID: 38717196 PMCID: PMC11077965 DOI: 10.1128/mbio.00690-24] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/06/2024] [Accepted: 03/08/2024] [Indexed: 05/12/2024] Open
Abstract
Extracellular cytochrome filaments are proposed to serve as conduits for long-range extracellular electron transfer. The primary functional physiological evidence has been the reported inhibition of Geobacter sulfurreducens Fe(III) oxide reduction when the gene for the filament-forming cytochrome OmcS is deleted. Here we report that the OmcS-deficient strain from that original report reduces Fe(III) oxide as well as the wild-type, as does a triple mutant in which the genes for the other known filament-forming cytochromes were also deleted. The triple cytochrome mutant displayed filaments with the same 3 nm diameter morphology and conductance as those produced by Escherichia coli heterologously expressing the G. sulfurreducens PilA pilin gene. Fe(III) oxide reduction was inhibited when the pilin gene in cytochrome-deficient mutants was modified to yield poorly conductive 3 nm diameter filaments. The results are consistent with the concept that 3 nm diameter electrically conductive pili (e-pili) are required for G. sulfurreducens long-range extracellular electron transfer. In contrast, rigorous physiological functional evidence is lacking for cytochrome filaments serving as conduits for long-range electron transport. IMPORTANCE Unraveling microbial extracellular electron transfer mechanisms has profound implications for environmental processes and advancing biological applications. This study on Geobacter sulfurreducens challenges prevailing beliefs on cytochrome filaments as crucial components thought to facilitate long-range electron transport. The discovery of an OmcS-deficient strain's unexpected effectiveness in Fe(III) oxide reduction prompted a reevaluation of the key conduits for extracellular electron transfer. By exploring the impact of genetic modifications on G. sulfurreducens' performance, this research sheds light on the importance of 3-nm diameter electrically conductive pili in Fe(III) oxide reduction. Reassessing these mechanisms is essential for uncovering the true drivers of extracellular electron transfer in microbial systems, offering insights that could revolutionize applications across diverse fields.
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Affiliation(s)
- Ingrid A. Schwarz
- Department of Biomolecular Sciences, Central Connecticut State University, New Britain, Connecticut, USA
| | - Baha Alsaqri
- Department of Biomolecular Sciences, Central Connecticut State University, New Britain, Connecticut, USA
| | - Yassir Lekbach
- Department of Microbiology, University of Massachusetts Amherst, Amherst, Massachusetts, USA
| | - Kathryn Henry
- Department of Physical and Biological Sciences, Western New England University, Springfield, Massachusetts, USA
| | - Sydney Gorman
- Department of Physical and Biological Sciences, Western New England University, Springfield, Massachusetts, USA
| | - Trevor Woodard
- Department of Microbiology, University of Massachusetts Amherst, Amherst, Massachusetts, USA
| | - Laura Dion
- Department of Physical and Biological Sciences, Western New England University, Springfield, Massachusetts, USA
| | - Lauren Real
- Department of Biomolecular Sciences, Central Connecticut State University, New Britain, Connecticut, USA
| | - Dawn E. Holmes
- Department of Microbiology, University of Massachusetts Amherst, Amherst, Massachusetts, USA
- Department of Physical and Biological Sciences, Western New England University, Springfield, Massachusetts, USA
| | - Jessica A. Smith
- Department of Biomolecular Sciences, Central Connecticut State University, New Britain, Connecticut, USA
- Department of Microbiology, University of Massachusetts Amherst, Amherst, Massachusetts, USA
| | - Derek R. Lovley
- Department of Microbiology, University of Massachusetts Amherst, Amherst, Massachusetts, USA
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4
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Ye Y, Zhang L, Hong X, Chen M, Liu X, Zhou S. Interspecies ecological competition rejuvenates decayed Geobacter electroactive biofilm. THE ISME JOURNAL 2024; 18:wrae118. [PMID: 38916438 PMCID: PMC11227281 DOI: 10.1093/ismejo/wrae118] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/18/2024] [Revised: 06/05/2024] [Accepted: 06/23/2024] [Indexed: 06/26/2024]
Abstract
Bioelectrochemical systems (BESs) exploit electroactive biofilms (EABs) for promising applications in biosensing, wastewater treatment, energy production, and chemical biosynthesis. However, during the operation of BESs, EABs inevitably decay. Seeking approaches to rejuvenate decayed EABs is critical for the sustainability and practical application of BESs. Prophage induction has been recognized as the primary reason for EAB decay. Herein, we report that introducing a competitive species of Geobacter uraniireducens suspended prophage induction in Geobacter sulfurreducens and thereby rejuvenated the decayed G. sulfurreducens EAB. The transcriptomic profile of G. sulfurreducens demonstrated that the addition of G. uraniireducens significantly affected the expression of metabolism- and stress response system-related genes and in particular suppressed the induction of phage-related genes. Mechanistic analyses revealed that interspecies ecological competition exerted by G. uraniireducens suppressed prophage induction. Our findings not only reveal a novel strategy to rejuvenate decayed EABs, which is significant for the sustainability of BESs, but also provide new knowledge for understanding phage-host interactions from an ecological perspective, with implications for developing therapies to defend against phage attack.
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Affiliation(s)
- Yin Ye
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Lu Zhang
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Xiaohui Hong
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Man Chen
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Xing Liu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
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Lu Z, Cheng X, Xie J, Li Z, Li X, Jiang X, Zhu D. Iron-based multi-carbon composite and Pseudomonas furukawaii ZS1 co-affect nitrogen removal, microbial community dynamics and metabolism pathways in low-temperature aquaculture wastewater. JOURNAL OF ENVIRONMENTAL MANAGEMENT 2024; 349:119471. [PMID: 37913618 DOI: 10.1016/j.jenvman.2023.119471] [Citation(s) in RCA: 2] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/06/2023] [Revised: 10/24/2023] [Accepted: 10/25/2023] [Indexed: 11/03/2023]
Abstract
Aerobic denitrification is the key process in the elimination of nitrogen from aquaculture wastewater, especially for wastewater with high dissolved oxygen and low carbon/nitrogen (C/N) ratio. However, a low C/N ratio, especially in low-temperature environments, restricts the activity of aerobic denitrifiers and decreases the nitrogen elimination efficiency. In this study, an iron-based multi-solid carbon source composite that immobilized aerobic denitrifying bacteria ZS1 (IMCSCP) was synthesized to treat aerobic (DO > 5 mg/L), low temperature (<15 °C) and low C/N ratio (C/N = 4) aquaculture wastewater. The results showed that the sequencing batch biofilm reactor (SBBR) packed with IMCSCP exhibited the highest nitrogen removal performance, with removal rates of 95.63% and 85.44% for nitrate nitrogen and total nitrogen, respectively, which were 33.03% and 30.75% higher than those in the reactor filled with multi-solid carbon source composite (MCSC). Microbial community and network analysis showed that Pseudomonas furukawaii ZS1 successfully colonized the SBBR filled with IMCSCP, and Exiguobacterium, Cellulomonas and Pseudomonas were essential for the nitrogen elimination. Metagenomic analysis showed that an increase in gene abundance related to carbon metabolism, nitrogen metabolism, extracellular polymer substance synthesis and electron transfer in the IMCSCP, enabling denitrification in the SBBR to be achieved via multiple pathways. The results of this study provided new insights into the microbial removal mechanism of nitrogen in SBBR packed with IMCSCP at low temperatures.
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Affiliation(s)
- Zhuoyin Lu
- School of Civil Engineering and Transportation, State Key Laboratory of Subtropical Building and Urban Science, South China University of Technology, Guangzhou, 510641, China
| | - Xiangju Cheng
- School of Civil Engineering and Transportation, State Key Laboratory of Subtropical Building and Urban Science, South China University of Technology, Guangzhou, 510641, China.
| | - Jun Xie
- Key Laboratory of Tropical & Subtropical Fishery Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, 510380, China
| | - Zhifei Li
- School of Civil Engineering and Transportation, State Key Laboratory of Subtropical Building and Urban Science, South China University of Technology, Guangzhou, 510641, China; Key Laboratory of Tropical & Subtropical Fishery Resource Application & Cultivation, Ministry of Agriculture, Pearl River Fisheries Research Institute, Chinese Academy of Fishery Sciences, Guangzhou, 510380, China
| | - Xiangyang Li
- Guanghuiyuan Hydraulic Construction Engineering Co., Ltd., Shenzhen, 518020, China; Guangdong Engineering Technology Research Center of Smart and Ecological River, Guangzhou, 510640, China
| | - Xiaotian Jiang
- Guanghuiyuan Hydraulic Construction Engineering Co., Ltd., Shenzhen, 518020, China
| | - Dantong Zhu
- School of Civil Engineering and Transportation, State Key Laboratory of Subtropical Building and Urban Science, South China University of Technology, Guangzhou, 510641, China
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6
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Abstract
Extracellular electron transfer (EET) is the physiological process that enables the reduction or oxidation of molecules and minerals beyond the surface of a microbial cell. The first bacteria characterized with this capability were Shewanella and Geobacter, both reported to couple their growth to the reduction of iron or manganese oxide minerals located extracellularly. A key difference between EET and nearly every other respiratory activity on Earth is the need to transfer electrons beyond the cell membrane. The past decade has resolved how well-conserved strategies conduct electrons from the inner membrane to the outer surface. However, recent data suggest a much wider and less well understood collection of mechanisms enabling electron transfer to distant acceptors. This review reflects the current state of knowledge from Shewanella and Geobacter, specifically focusing on transfer across the outer membrane and beyond-an activity that enables reduction of highly variable minerals, electrodes, and even other organisms.
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Affiliation(s)
- J A Gralnick
- BioTechnology Institute and Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA; ,
| | - D R Bond
- BioTechnology Institute and Department of Plant and Microbial Biology, University of Minnesota, St. Paul, Minnesota, USA; ,
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7
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Myers B, Catrambone F, Allen S, Hill PJ, Kovacs K, Rawson FJ. Engineering nanowires in bacteria to elucidate electron transport structural-functional relationships. Sci Rep 2023; 13:8843. [PMID: 37258594 DOI: 10.1038/s41598-023-35553-2] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2023] [Accepted: 05/19/2023] [Indexed: 06/02/2023] Open
Abstract
Bacterial pilin nanowires are protein complexes, suggested to possess electroactive capabilities forming part of the cells' bioenergetic programming. Their role is thought to be linked to facilitating electron transfer between cells and the external environment to permit metabolism and cell-to-cell communication. There is a significant debate, with varying hypotheses as to the nature of the proteins currently lying between type-IV pilin-based nanowires and polymerised cytochrome-based filaments. Importantly, to date, there is a very limited structure-function analysis of these structures within whole bacteria. In this work, we engineered Cupriavidus necator H16, a model autotrophic organism to express differing aromatic modifications of type-IV pilus proteins to establish structure-function relationships on conductivity and the effects this has on pili structure. This was achieved via a combination of high-resolution PeakForce tunnelling atomic force microscopy (PeakForce TUNA™) technology, alongside conventional electrochemical approaches enabling the elucidation of conductive nanowires emanating from whole bacterial cells. This work is the first example of functional type-IV pili protein nanowires produced under aerobic conditions using a Cupriavidus necator chassis. This work has far-reaching consequences in understanding the basis of bio-electrical communication between cells and with their external environment.
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Affiliation(s)
- Ben Myers
- Bioelectronics Laboratory, Regenerative Medicine and Cellular Therapies, School of Pharmacy, Biodiscovery Institute, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
- Molecular Therapeutics and Formulation Division, School of Pharmacy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Francesco Catrambone
- BBSRC/EPSRC Synthetic Biology Research Centre, School of Life Sciences, Biodiscovery Institute, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Stephanie Allen
- Molecular Therapeutics and Formulation Division, School of Pharmacy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK
| | - Phil J Hill
- Division of Microbiology, Brewing and Biotechnology, School of Biosciences, University of Nottingham, Sutton Bonington Campus, Leicestershire, LE12 5RD, UK
| | - Katalin Kovacs
- Bioelectronics Laboratory, Regenerative Medicine and Cellular Therapies, School of Pharmacy, Biodiscovery Institute, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
- Molecular Therapeutics and Formulation Division, School of Pharmacy, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
| | - Frankie J Rawson
- Bioelectronics Laboratory, Regenerative Medicine and Cellular Therapies, School of Pharmacy, Biodiscovery Institute, University of Nottingham, University Park, Nottingham, NG7 2RD, UK.
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8
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Liu X, Ye Y, Zhang Z, Rensing C, Zhou S, Nealson KH. Prophage Induction Causes Geobacter Electroactive Biofilm Decay. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2023; 57:6196-6204. [PMID: 36997849 DOI: 10.1021/acs.est.2c08443] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/19/2023]
Abstract
Sustaining a metabolically active electroactive biofilm (EAB) is essential for the high efficiency and durable operation of microbial fuel cells (MFCs). However, EABs usually decay during long-term operation, and, until now, the causes remain unknown. Here, we report that lysogenic phages can cause EAB decay in Geobacter sulfurreducens fuel cells. A cross-streak agar assay and bioinformatic analysis revealed the presence of prophages on the G. sulfurreducens genome, and a mitomycin C induction assay revealed the lysogenic to lytic transition of those prophages, resulting in a progressive decay in both current generation and the EAB. Furthermore, the addition of phages purified from decayed EAB resulted in accelerated decay of the EAB, thereafter contributing to a faster decline in current generation; otherwise, deleting prophage-related genes rescued the decay process. Our study provides the first evidence of an interaction between phages and electroactive bacteria and suggests that attack by phages is a primary cause of EAB decay, having significant implications in bioelectrochemical systems.
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Affiliation(s)
- Xing Liu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Yin Ye
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Zhishuai Zhang
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Christopher Rensing
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou 350002, China
| | - Kenneth H Nealson
- Department of Earth Science, University of Southern California, Los Angeles, California 90089, United States
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9
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Verma M, Singh V, Mishra V. Moving towards the enhancement of extracellular electron transfer in electrogens. World J Microbiol Biotechnol 2023; 39:130. [PMID: 36959310 DOI: 10.1007/s11274-023-03582-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2023] [Accepted: 03/15/2023] [Indexed: 03/25/2023]
Abstract
Electrogens are very common in nature and becoming a contemporary theme for research as they can be exploited for extracellular electron transfer. Extracellular electron transfer is the key mechanism behind bioelectricity generation and bioremediation of pollutants via microbes. Extracellular electron transfer mechanisms for electrogens other than Shewanella and Geobacter are less explored. An efficient extracellular electron transfer system is crucial for the sustainable future of bioelectrochemical systems. At present, the poor extracellular electron transfer efficiency remains a decisive factor in limiting the development of efficient bioelectrochemical systems. In this review article, the EET mechanisms in different electrogens (bacteria and yeast) have been focused. Apart from the well-known electron transfer mechanisms of Shewanella oneidensis and Geobacter metallireducens, a brief introduction of the EET pathway in Rhodopseudomonas palustris TIE-1, Sideroxydans lithotrophicus ES-1, Thermincola potens JR, Lysinibacillus varians GY32, Carboxydothermus ferrireducens, Enterococcus faecalis and Saccharomyces cerevisiae have been included. In addition to this, the article discusses the several approaches to anode modification and genetic engineering that may be used in order to increase the rate of extracellular electron transfer. In the side lines, this review includes the engagement of the electrogens for different applications followed by the future perspective of efficient extracellular electron transfer.
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Affiliation(s)
- Manisha Verma
- School of Biochemical Engineering, IIT (BHU), 221005, Varanasi, India
| | - Vishal Singh
- School of Biochemical Engineering, IIT (BHU), 221005, Varanasi, India
| | - Vishal Mishra
- School of Biochemical Engineering, IIT (BHU), 221005, Varanasi, India.
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10
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Fessler M, Madsen JS, Zhang Y. Conjugative plasmids inhibit extracellular electron transfer in Geobacter sulfurreducens. Front Microbiol 2023; 14:1150091. [PMID: 37007462 PMCID: PMC10063792 DOI: 10.3389/fmicb.2023.1150091] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2023] [Accepted: 02/20/2023] [Indexed: 03/19/2023] Open
Abstract
Geobacter sulfurreducens is part of a specialized group of microbes with the unique ability to exchange electrons with insoluble materials, such as iron oxides and electrodes. Therefore, G. sulfurreducens plays an essential role in the biogeochemical iron cycle and microbial electrochemical systems. In G. sulfurreducens this ability is primarily dependent on electrically conductive nanowires that link internal electron flow from metabolism to solid electron acceptors in the extracellular environment. Here we show that when carrying conjugative plasmids, which are self-transmissible plasmids that are ubiquitous in environmental bacteria, G. sulfurreducens reduces insoluble iron oxides at much slower rates. This was the case for all three conjugative plasmids tested (pKJK5, RP4 and pB10). Growth with electron acceptors that do not require expression of nanowires was, on the other hand, unaffected. Furthermore, iron oxide reduction was also inhibited in Geobacter chapellei, but not in Shewanella oneidensis where electron export is nanowire-independent. As determined by transcriptomics, presence of pKJK5 reduces transcription of several genes that have been shown to be implicated in extracellular electron transfer in G. sulfurreducens, including pilA and omcE. These results suggest that conjugative plasmids can in fact be very disadvantageous for the bacterial host by imposing specific phenotypic changes, and that these plasmids may contribute to shaping the microbial composition in electrode-respiring biofilms in microbial electrochemical reactors.
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Affiliation(s)
- Mathias Fessler
- Department of Environmental and Resource Engineering, Technical University of Denmark, Kongens Lyngby, Denmark
| | - Jonas Stenløkke Madsen
- Section of Microbiology, Department of Biology, University of Copenhagen, Copenhagen, Denmark
| | - Yifeng Zhang
- Department of Environmental and Resource Engineering, Technical University of Denmark, Kongens Lyngby, Denmark
- *Correspondence: Yifeng Zhang,
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11
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Wang Z, Hu Y, Dong Y, Shi L, Jiang Y. Enhancing electrical outputs of the fuel cells with Geobacter sulferreducens by overexpressing nanowire proteins. Microb Biotechnol 2023; 16:534-545. [PMID: 36815664 PMCID: PMC9948223 DOI: 10.1111/1751-7915.14128] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2022] [Revised: 07/19/2022] [Accepted: 07/26/2022] [Indexed: 11/28/2022] Open
Abstract
Protein nanowires are critical electroactive components for electron transfer of Geobacter sulfurreducens biofilm. To determine the applicability of the nanowire proteins in improving bioelectricity production, their genes including pilA, omcZ, omcS and omcT were overexpressed in G. sulfurreducens. The voltage outputs of the constructed strains were higher than that of the control strain with the empty vector (0.470-0.578 vs. 0.355 V) in microbial fuel cells (MFCs). As a result, the power density of the constructed strains (i.e. 1.39-1.58 W m-2 ) also increased by 2.62- to 2.97-fold as compared to that of the control strain. Overexpression of nanowire proteins also improved biofilm formation on electrodes with increased protein amount and thickness of biofilms. The normalized power outputs of the constructed strains were 0.18-0.20 W g-1 that increased by 74% to 93% from that of the control strain. Bioelectrochemical analyses further revealed that the biofilms and MFCs with the constructed strains had stronger electroactivity and smaller internal resistance, respectively. Collectively, these results demonstrate for the first time that overexpression of nanowire proteins increases the biomass and electroactivity of anode-attached microbial biofilms. Moreover, this study provides a new way for enhancing the electrical outputs of MFCs.
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Affiliation(s)
- Zhigao Wang
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, Hubei, China
| | - Yidan Hu
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, Hubei, China.,Hubei Key Laboratory of Wetland Evolution and Eco-Restoration, Wuhan, Hubei, China
| | - Yiran Dong
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, Hubei, China.,Hubei Key Laboratory of Wetland Evolution and Eco-Restoration, Wuhan, Hubei, China.,State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, Hubei, China.,Hubei Key Laboratory of Yangtze Catchment Environmental Aquatic Science, China University of Geosciences, Wuhan, Hubei, China.,State Environmental Protection Key Laboratory of Source Apportionment and Control of Aquatic Pollution, Ministry of Ecology and Environment, China University of Geosciences, Wuhan, Hubei, China
| | - Liang Shi
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, Hubei, China.,State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, Hubei, China.,Hubei Key Laboratory of Yangtze Catchment Environmental Aquatic Science, China University of Geosciences, Wuhan, Hubei, China.,State Environmental Protection Key Laboratory of Source Apportionment and Control of Aquatic Pollution, Ministry of Ecology and Environment, China University of Geosciences, Wuhan, Hubei, China
| | - Yongguang Jiang
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, Hubei, China.,Hubei Key Laboratory of Wetland Evolution and Eco-Restoration, Wuhan, Hubei, China
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12
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Lovley DR. Response to Wang et al.: evidence contradicting the cytochrome-only model. Trends Microbiol 2023; 31:548-549. [PMID: 37005158 DOI: 10.1016/j.tim.2023.03.006] [Citation(s) in RCA: 1] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/13/2023] [Revised: 03/07/2023] [Accepted: 03/13/2023] [Indexed: 04/03/2023]
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Ou J, Wen J, Tan W, Luo X, Cai J, He X, Zhou L, Yuan Y. A data-driven approach for understanding the structure dependence of redox activity in humic substances. ENVIRONMENTAL RESEARCH 2023; 219:115142. [PMID: 36566968 DOI: 10.1016/j.envres.2022.115142] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/11/2022] [Revised: 12/03/2022] [Accepted: 12/17/2022] [Indexed: 06/17/2023]
Abstract
Humic substances (HS) can facilitate electron transfer during biogeochemical processes due to their redox properties, but the structure-redox activity relationships are still difficult to describe and poorly understood. Herein, the linear (Partial Least Squares regressions; PLS) and nonlinear (artificial neural network; ANN) models were applied to monitor the structure dependence of HS redox activities in terms of electron accepting (EAC), electron donating (EDC) and overall electron transfer capacities (ETC) using its physicochemical features as input variables. The PLS model exhibited a moderate ability with R2 values of 0.60, 0.53 and 0.65 to evaluate EAC, EDC and ETC, respectively. The variable influence in the projection (VIP) scores of the PLS identified that the phenols, quinones and aromatic systems were particularly important for describing the redox activities of HS. Compared with the PLS model, the back-propagation ANN model achieved higher performance with R2 values of 0.81, 0.65 and 0.78 for monitoring the EAC, EDC and ETC, respectively. Sensitivity analysis of the ANN separately identified that the EAC highly depended on quinones, aromatics and protein-like fluorophores, while the EDC depended on phenols, aromatics and humic-like fluorophores (or stable free radicals). Additionally, carboxylic groups were the best indicator for evaluating both the EAC and EDC. Good model performances were obtained from the selected features via the PLS and sensitivity analysis, further confirming the accuracy of describing the structure-redox activity relationships with these analyses. This study provides a potential approach for identifying the structure-activity relationships of HS and an efficient machine-learning model for predicting HS redox activities.
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Affiliation(s)
- Jiajun Ou
- School of Automation, Guangdong University of Technology, Guangzhou, 510006, China
| | - Junlin Wen
- Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Guangdong University of Technology, Guangzhou, 510006, China; School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou, 510006, China.
| | - Wenbing Tan
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China; State Environmental Protection Key Laboratory of Simulation and Control of Groundwater Pollution, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China
| | - Xiaoshan Luo
- Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Guangdong University of Technology, Guangzhou, 510006, China; School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou, 510006, China
| | - Jiexuan Cai
- Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Guangdong University of Technology, Guangzhou, 510006, China; School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou, 510006, China
| | - Xiaosong He
- State Key Laboratory of Environmental Criteria and Risk Assessment, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China; State Environmental Protection Key Laboratory of Simulation and Control of Groundwater Pollution, Chinese Research Academy of Environmental Sciences, Beijing, 100012, China
| | - Lihua Zhou
- School of Biomedical and Pharmaceutical Sciences, Guangdong University of Technology, Guangzhou 510006, China
| | - Yong Yuan
- Guangdong Key Laboratory of Environmental Catalysis and Health Risk Control, Guangdong University of Technology, Guangzhou, 510006, China; School of Environmental Science and Engineering, Institute of Environmental Health and Pollution Control, Guangdong University of Technology, Guangzhou, 510006, China.
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Genetic Manipulation of Desulfovibrio ferrophilus and Evaluation of Fe(III) Oxide Reduction Mechanisms. Microbiol Spectr 2022; 10:e0392222. [PMID: 36445123 PMCID: PMC9769857 DOI: 10.1128/spectrum.03922-22] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/02/2022] Open
Abstract
The sulfate-reducing microbe Desulfovibrio ferrophilus is of interest due to its relatively rare ability to also grow with Fe(III) oxide as an electron acceptor and its rapid corrosion of metallic iron. Previous studies have suggested multiple agents for D. ferrophilus extracellular electron exchange including a soluble electron shuttle, electrically conductive pili, and outer surface multiheme c-type cytochromes. However, the previous lack of a strategy for genetic manipulation of D. ferrophilus limited mechanistic investigations. We developed an electroporation-mediated transformation method that enabled replacement of D. ferrophilus genes of interest with an antibiotic resistance gene via double-crossover homologous recombination. Genes were identified that are essential for flagellum-based motility and the expression of the two types of D. ferrophilus pili. Disrupting flagellum-based motility or expression of either of the two pili did not inhibit Fe(III) oxide reduction, nor did deleting genes for multiheme c-type cytochromes predicted to be associated with the outer membrane. Although redundancies in cytochrome or pilus function might explain some of these phenotypes, overall, the results are consistent with D. ferrophilus primarily reducing Fe(III) oxide via an electron shuttle. The finding that D. ferrophilus is genetically tractable not only will aid in elucidating further details of its mechanisms for Fe(III) oxide reduction but also provides a new experimental approach for developing a better understanding of some of its other unique features, such as the ability to corrode metallic iron at high rates and accept electrons from negatively poised electrodes. IMPORTANCE Desulfovibrio ferrophilus is an important pure culture model for Fe(III) oxide reduction and the corrosion of iron-containing metals in anaerobic marine environments. This study demonstrates that D. ferrophilus is genetically tractable, an important advance for elucidating the mechanisms by which it interacts with extracellular electron acceptors and donors. The results demonstrate that there is not one specific outer surface multiheme D. ferrophilus c-type cytochrome that is essential for Fe(III) oxide reduction. This finding, coupled with the lack of apparent porin-cytochrome conduits encoded in the D. ferrophilus genome and the finding that deleting genes for pilus and flagellum expression did not inhibit Fe(III) oxide reduction, suggests that D. ferrophilus has adopted strategies for extracellular electron exchange that are different from those of intensively studied electroactive microbes like Shewanella and Geobacter species. Thus, the ability to genetically manipulate D. ferrophilus is likely to lead to new mechanistic concepts in electromicrobiology.
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Holmes DE, Zhou J, Smith JA, Wang C, Liu X, Lovley DR. Different outer membrane c-type cytochromes are involved in direct interspecies electron transfer to Geobacter or Methanosarcina species. MLIFE 2022; 1:272-286. [PMID: 38818222 PMCID: PMC10989804 DOI: 10.1002/mlf2.12037] [Citation(s) in RCA: 12] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Key Words] [Grants] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 04/26/2022] [Revised: 07/21/2022] [Accepted: 07/26/2022] [Indexed: 06/01/2024]
Abstract
Direct interspecies electron transfer (DIET) may be most important in methanogenic environments, but mechanistic studies of DIET to date have primarily focused on cocultures in which fumarate was the terminal electron acceptor. To better understand DIET with methanogens, the transcriptome of Geobacter metallireducens during DIET-based growth with G. sulfurreducens reducing fumarate was compared with G. metallireducens grown in coculture with diverse Methanosarcina. The transcriptome of G. metallireducens cocultured with G. sulfurreducens was significantly different from those with Methanosarcina. Furthermore, the transcriptome of G. metallireducens grown with Methanosarcina barkeri, which lacks outer-surface c-type cytochromes, differed from those of G. metallireducens cocultured with M. acetivorans or M. subterranea, which have an outer-surface c-type cytochrome that serves as an electrical connect for DIET. Differences in G. metallireducens expression patterns for genes involved in extracellular electron transfer were particularly notable. Cocultures with c-type cytochrome deletion mutant strains, ∆Gmet_0930, ∆Gmet_0557 and ∆Gmet_2896, never became established with G. sulfurreducens but adapted to grow with all three Methanosarcina. Two porin-cytochrome complexes, PccF and PccG, were important for DIET; however, PccG was more important for growth with Methanosarcina. Unlike cocultures with G. sulfurreducens and M. acetivorans, electrically conductive pili were not needed for growth with M. barkeri. Shewanella oneidensis, another electroactive microbe with abundant outer-surface c-type cytochromes, did not grow via DIET. The results demonstrate that the presence of outer-surface c-type cytochromes does not necessarily confer the capacity for DIET and emphasize the impact of the electron-accepting partner on the physiology of the electron-donating DIET partner.
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Affiliation(s)
- Dawn E. Holmes
- Department of MicrobiologyUniversity of Massachusetts‐AmherstAmherstMassachusettsUSA
- Department of Physical and Biological ScienceWestern New England UniversitySpringfieldMassachusettsUSA
| | - Jinjie Zhou
- Department of MicrobiologyUniversity of Massachusetts‐AmherstAmherstMassachusettsUSA
- Institute for Advanced StudyShenzhen UniversityShenzhenChina
| | - Jessica A. Smith
- Department of MicrobiologyUniversity of Massachusetts‐AmherstAmherstMassachusettsUSA
- Department of Biomolecular SciencesCentral Connecticut State UniversityNew BritainConnecticutUSA
| | - Caiqin Wang
- Department of MicrobiologyUniversity of Massachusetts‐AmherstAmherstMassachusettsUSA
- College of EnvironmentZhejiang University of TechnologyHangzhouChina
| | - Xinying Liu
- Department of MicrobiologyUniversity of Massachusetts‐AmherstAmherstMassachusettsUSA
- College of Environmental Science and EngineeringBeijing Forestry UniversityBeijingChina
| | - Derek R. Lovley
- Department of MicrobiologyUniversity of Massachusetts‐AmherstAmherstMassachusettsUSA
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Yu H, He Z, He Z, Yan Q, Shu L. Soil Amoebae Affect Iron and Chromium Reduction through Preferential Predation between Two Metal-Reducing Bacteria. ENVIRONMENTAL SCIENCE & TECHNOLOGY 2022; 56:9052-9062. [PMID: 35544746 DOI: 10.1021/acs.est.1c08069] [Citation(s) in RCA: 10] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/15/2023]
Abstract
Soil protists are essential but often overlooked in soil and could impact microbially driven element cycling in natural ecosystems. However, how protists influence heavy metal cycling in soil remains poorly understood. In this study, we used a model protist, Dictyostelium discoideum, to explore the effect of interactions between soil amoeba and metal-reducing bacteria on the reduction of soil Fe(III) and Cr(VI). We found that D. discoideum could preferentially prey on the Fe(III)-reducing bacterium Shewanella decolorationis S12 and significantly decrease its biomass. Surprisingly, this predation pressure also stimulated the activity of a single S. decolorationis S12 bacterium to reduce Fe(III) by enhancing the content of electron-transfer protein cyt c, intracellular ATP synthesis, and reactive oxygen species (e.g., H2O2). We also found that D. discoideum could not prey on the Cr(VI)-reducing bacterium Brevibacillus laterosporus. In contrast, B. laterosporus became edible to amoebae in the presence of S. decolorationis S12, and their Cr(VI) reduction ability decreased under amoeba predation pressure. This study provides direct evidence that protists can affect the Cr and Fe cycling via the elective predation pressure on the metal-reducing bacteria, broadening our horizons of predation of protists on soil metal cycling.
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Affiliation(s)
- Huang Yu
- Environmental Microbiomics Research Center, School of Environmental Science and Engineering, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), State Key Laboratory for Biocontrol, Sun Yat-sen University, Guangzhou 510006, China
| | - Zhenzhen He
- Environmental Microbiomics Research Center, School of Environmental Science and Engineering, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), State Key Laboratory for Biocontrol, Sun Yat-sen University, Guangzhou 510006, China
| | - Zhili He
- Environmental Microbiomics Research Center, School of Environmental Science and Engineering, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), State Key Laboratory for Biocontrol, Sun Yat-sen University, Guangzhou 510006, China
- College of Agronomy, Hunan Agricultural University, Changsha 410128, China
| | - Qingyun Yan
- Environmental Microbiomics Research Center, School of Environmental Science and Engineering, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), State Key Laboratory for Biocontrol, Sun Yat-sen University, Guangzhou 510006, China
| | - Longfei Shu
- Environmental Microbiomics Research Center, School of Environmental Science and Engineering, Southern Marine Science and Engineering Guangdong Laboratory (Zhuhai), State Key Laboratory for Biocontrol, Sun Yat-sen University, Guangzhou 510006, China
- Guangdong Provincial Key Laboratory of Environmental Pollution Control and Remediation Technology, Sun Yat-sen University, Guangzhou 510275, China
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Zhuang Z, Xia X, Yang G, Zhuang L. The Role of Exopolysaccharides in Direct Interspecies Electron Transfer. Front Microbiol 2022; 13:927246. [PMID: 35783440 PMCID: PMC9244359 DOI: 10.3389/fmicb.2022.927246] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/24/2022] [Accepted: 05/23/2022] [Indexed: 11/14/2022] Open
Abstract
Direct interspecies electron transfer (DIET) is an effective mechanism for microbial species to exchange electrons cooperatively during syntrophic metabolism. It is generally accepted that DIET is mainly mediated by electrically conductive pili and outer surface c-type cytochromes (c-Cyts). However, as an extracellular matrix is ubiquitous and abundant on the surface of microorganisms, the effect and mechanism of exopolysaccharides on DIET are still unclear. This study constructed a co-culture of exopolysaccharides-deficient Geobacter sulfurreducens with Geobacter metallireducens to explore the role of exopolysaccharides in DIET. Results revealed that the deficiency of exopolysaccharides extended the metabolic period of the co-culture by 44.4% and changed the proportions of each species in the co-culture. The exopolysaccharides-deficient co-culture failed to form large, tight spherical aggregates and the expression of c-Cyts and pili was decreased. The addition of magnetite and granular activated carbon (GAC), respectively, might compensate for the functions of c-Cyts and pili in the first generation of co-culture, but the stimulatory effect on the metabolic stable period co-culture was fairly limited. These findings demonstrate that non-conductive exopolysaccharides are an important component of DIET aggregates and an extracellular matrix for DIET-required c-Cyts.
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Lovley DR. On the Existence of Pilin-Based Microbial Nanowires. Front Microbiol 2022; 13:872610. [PMID: 35733974 PMCID: PMC9207759 DOI: 10.3389/fmicb.2022.872610] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2022] [Accepted: 05/17/2022] [Indexed: 11/13/2022] Open
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Conners EM, Rengasamy K, Bose A. "Electroactive biofilms: how microbial electron transfer enables bioelectrochemical applications". J Ind Microbiol Biotechnol 2022; 49:6563884. [PMID: 35381088 PMCID: PMC9338886 DOI: 10.1093/jimb/kuac012] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/16/2021] [Accepted: 03/30/2022] [Indexed: 11/22/2022]
Abstract
Microbial biofilms are ubiquitous. In marine and freshwater ecosystems, microbe–mineral interactions sustain biogeochemical cycles, while biofilms found on plants and animals can range from pathogens to commensals. Moreover, biofouling and biocorrosion represent significant challenges to industry. Bioprocessing is an opportunity to take advantage of biofilms and harness their utility as a chassis for biocommodity production. Electrochemical bioreactors have numerous potential applications, including wastewater treatment and commodity production. The literature examining these applications has demonstrated that the cell–surface interface is vital to facilitating these processes. Therefore, it is necessary to understand the state of knowledge regarding biofilms’ role in bioprocessing. This mini-review discusses bacterial biofilm formation, cell–surface redox interactions, and the role of microbial electron transfer in bioprocesses. It also highlights some current goals and challenges with respect to microbe-mediated bioprocessing and future perspectives.
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Affiliation(s)
- Eric M Conners
- Department of Biology. One Brookings Drive, Washington University in St. Louis, Missouri, 63105, USA
| | - Karthikeyan Rengasamy
- Department of Biology. One Brookings Drive, Washington University in St. Louis, Missouri, 63105, USA
| | - Arpita Bose
- Department of Biology. One Brookings Drive, Washington University in St. Louis, Missouri, 63105, USA
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Zhuang Z, Yang G, Zhuang L. Exopolysaccharides matrix affects the process of extracellular electron transfer in electroactive biofilm. THE SCIENCE OF THE TOTAL ENVIRONMENT 2022; 806:150713. [PMID: 34606863 DOI: 10.1016/j.scitotenv.2021.150713] [Citation(s) in RCA: 17] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2021] [Revised: 08/19/2021] [Accepted: 09/27/2021] [Indexed: 05/20/2023]
Abstract
The applications of bioelectrochemical systems (BESs) in the field of environment and energy are achieved through the bioelectrocatalytic process of electroactive biofilms. As a primary component of biofilm, the role of exopolysaccharides in electroactive biofilm in BESs is poorly understood. This study constructed an exopolysaccharides-deficient Geobacter sulfurreducens-based BES to explore the role of exopolysaccharides in electroactive biofilm. Compared with the wild type, the mutant biofilm expressing less exopolysaccharides decreased the capacity of current generation. In the mutant biofilm, the content of exopolysaccharides decreased significantly, resulting in a thinner biofilm and lower cell viability compared with the wild-type biofilm. However, the mutant with overexpressed pili developed a mature biofilm with extended time, which indicating the importance of exopolysaccharides for early biofilm formation and the compensatory role of pili in biofilm formation. The mutant biofilm had less content of c-type cytochromes (c-Cyts) and lower electrochemical activity of extracellular polymeric substances than the wild-type biofilm, suggesting a function of exopolysaccharides anchoring extracellular c-Cyts that essential to extracellular electron transfer (EET) in electroactive biofilms. Our findings demonstrated the essential role of exopolysaccharides in the process of EET in electroactive biofilm, which contributed to a better understanding and optimization of the performance of BESs.
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Affiliation(s)
- Zheng Zhuang
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Guiqin Yang
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China
| | - Li Zhuang
- Guangdong Key Laboratory of Environmental Pollution and Health, School of Environment, Jinan University, Guangzhou 510632, China.
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Hu Y, Wang Y, Han X, Shan Y, Li F, Shi L. Biofilm Biology and Engineering of Geobacter and Shewanella spp. for Energy Applications. Front Bioeng Biotechnol 2021; 9:786416. [PMID: 34926431 PMCID: PMC8683041 DOI: 10.3389/fbioe.2021.786416] [Citation(s) in RCA: 11] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/30/2021] [Accepted: 11/18/2021] [Indexed: 01/04/2023] Open
Abstract
Geobacter and Shewanella spp. were discovered in late 1980s as dissimilatory metal-reducing microorganisms that can transfer electrons from cytoplasmic respiratory oxidation reactions to external metal-containing minerals. In addition to mineral-based electron acceptors, Geobacter and Shewanella spp. also can transfer electrons to electrodes. The microorganisms that have abilities to transfer electrons to electrodes are known as exoelectrogens. Because of their remarkable abilities of electron transfer, Geobacter and Shewanella spp. have been the two most well studied groups of exoelectrogens. They are widely used in bioelectrochemical systems (BESs) for various biotechnological applications, such as bioelectricity generation via microbial fuel cells. These applications mostly associate with Geobacter and Shewanella biofilms grown on the surfaces of electrodes. Geobacter and Shewanella biofilms are electrically conductive, which is conferred by matrix-associated electroactive components such as c-type cytochromes and electrically conductive nanowires. The thickness and electroactivity of Geobacter and Shewanella biofilms have a significant impact on electron transfer efficiency in BESs. In this review, we first briefly discuss the roles of planktonic and biofilm-forming Geobacter and Shewanella cells in BESs, and then review biofilm biology with the focus on biofilm development, biofilm matrix, heterogeneity in biofilm and signaling regulatory systems mediating formation of Geobacter and Shewanella biofilms. Finally, we discuss strategies of Geobacter and Shewanella biofilm engineering for improving electron transfer efficiency to obtain enhanced BES performance.
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Affiliation(s)
- Yidan Hu
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, China
| | - Yinghui Wang
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, China
| | - Xi Han
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, China
| | - Yawei Shan
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, China
| | - Feng Li
- Key Laboratory of Systems Bioengineering (Ministry of Education), SynBio Research Platform, Collaborative Innovation Center of Chemical Science and Engineering, School of Chemical Engineering and Technology, Tianjin University, Tianjin, China
| | - Liang Shi
- Department of Biological Sciences and Technology, School of Environmental Studies, China University of Geosciences, Wuhan, China.,State Key Laboratory of Biogeology and Environmental Geology, China University of Geosciences, Wuhan, China.,Hubei Key Laboratory of Yangtze Catchment Environmental Aquatic Science, China University of Geosciences, Wuhan, China.,State Environmental Protection Key Laboratory of Source Apportionment and Control of Aquatic Pollution, Ministry of Ecology and Environment, Wuhan, China
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Bird LJ, Kundu BB, Tschirhart T, Corts AD, Su L, Gralnick JA, Ajo-Franklin CM, Glaven SM. Engineering Wired Life: Synthetic Biology for Electroactive Bacteria. ACS Synth Biol 2021; 10:2808-2823. [PMID: 34637280 DOI: 10.1021/acssynbio.1c00335] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022]
Abstract
Electroactive bacteria produce or consume electrical current by moving electrons to and from extracellular acceptors and donors. This specialized process, known as extracellular electron transfer, relies on pathways composed of redox active proteins and biomolecules and has enabled technologies ranging from harvesting energy on the sea floor, to chemical sensing, to carbon capture. Harnessing and controlling extracellular electron transfer pathways using bioengineering and synthetic biology promises to heighten the limits of established technologies and open doors to new possibilities. In this review, we provide an overview of recent advancements in genetic tools for manipulating native electroactive bacteria to control extracellular electron transfer. After reviewing electron transfer pathways in natively electroactive organisms, we examine lessons learned from the introduction of extracellular electron transfer pathways into Escherichia coli. We conclude by presenting challenges to future efforts and give examples of opportunities to bioengineer microbes for electrochemical applications.
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Affiliation(s)
- Lina J. Bird
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Biki B. Kundu
- PhD Program in Systems, Synthetic, and Physical Biology, Rice University, Houston, Texas 77005, United States
| | - Tanya Tschirhart
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375, United States
| | - Anna D. Corts
- Joyn Bio, Boston, Massachusetts 02210, United States
| | - Lin Su
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing 210018, People’s Republic of China
- Department of Chemistry, University of Cambridge, Cambridge CB2 1EW, United Kingdom
| | - Jeffrey A. Gralnick
- Department of Plant and Microbial Biology, BioTechnology Institute, University of Minnesota, St. Paul, Minnesota 55108, United States
| | | | - Sarah M. Glaven
- Center for Bio/Molecular Science and Engineering, Naval Research Laboratory, Washington, D.C. 20375, United States
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Generation of High Current Densities in Geobacter sulfurreducens Lacking the Putative Gene for the PilB Pilus Assembly Motor. Microbiol Spectr 2021; 9:e0087721. [PMID: 34585977 PMCID: PMC8557921 DOI: 10.1128/spectrum.00877-21] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Geobacter sulfurreducens is commonly employed as a model for the study of extracellular electron transport mechanisms in the Geobacter species. Deletion of pilB, which is known to encode the pilus assembly motor protein for type IV pili in other bacteria, has been proposed as an effective strategy for evaluating the role of electrically conductive pili (e-pili) in G. sulfurreducens extracellular electron transfer. In those studies, the inhibition of e-pili expression associated with pilB deletion was not demonstrated directly but was inferred from the observation that pilB deletion mutants produced lower current densities than wild-type cells. Here, we report that deleting pilB did not diminish current production. Conducting probe atomic force microscopy revealed filaments with the same diameter and similar current-voltage response as e-pili harvested from wild-type G. sulfurreducens or when e-pili are expressed heterologously from the G. sulfurreducens pilin gene in Escherichia coli. Immunogold labeling demonstrated that a G. sulfurreducens strain expressing a pilin monomer with a His tag continued to express His tag-labeled filaments when pilB was deleted. These results suggest that a reinterpretation of the results of previous studies on G. sulfurreducens pilB deletion strains may be necessary. IMPORTANCE Geobacter sulfurreducens is a model microbe for the study of biogeochemically and technologically significant processes, such as the reduction of Fe(III) oxides in soils and sediments, bioelectrochemical applications that produce electric current from waste organic matter or drive useful processes with the consumption of renewable electricity, direct interspecies electron transfer in anaerobic digestors and methanogenic soils and sediments, and metal corrosion. Elucidating the phenotypes associated with gene deletions is an important strategy for determining the mechanisms for extracellular electron transfer in G. sulfurreducens. The results reported here demonstrate that we cannot replicate the key phenotype reported for a gene deletion that has been central to the development of models for long-range electron transport in G. sulfurreducens.
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Cytochrome OmcS is not essential for extracellular electron transport via conductive pili in Geobacter sulfurreducens strain KN400. Appl Environ Microbiol 2021; 88:e0162221. [PMID: 34669448 DOI: 10.1128/aem.01622-21] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The multi-heme c-type cytochrome OmcS is one of the central components for extracellular electron transport in Geobacter sulfurreducens strain DL-1, but its role in other microbes, including other strains of G. sulfurreducens is currently a matter of debate. Therefore, we investigated the function of OmcS in G. sulfurreducens strain KN400, which is even more effective in extracellular electron transfer than strain DL-1. We found that deleting omcS from strain KN400 did not negatively impact the rate of Fe(III) oxide reduction and that the cells expressed conductive filaments. Replacing the wild-type pilin gene with the aro-5 pilin gene eliminated the OmcS-deficient strain's ability for electron transport to insoluble electron acceptors and diminished filament conductivity. These results are consistent with the concept that electrically conductive pili are the primary conduit for long-range electron transfer in G. sulfurreducens and closely related species. These findings, coupled with the lack of OmcS homologs in most other microbes capable of extracellular electron transfer, suggest that OmcS is not a common critical component for extracellular electron transfer. Importance OmcS has been widely studied and noted to be one of the key components for extracellular electron exchange by Geobacter sulfurreducens strain DL-1. However, the true importance of OmcS warrants further investigation as it is well-known that very few bacteria, even within the Geobacteraceae family, contain OmcS homologs, and many bacteria capable of extracellular electron transfer lack an abundance of any type of outer-surface c-type cytochrome. In addition, there is much debate regarding the importance of OmcS filaments in the mechanism of extracellular electron transport to insoluble electron acceptors by G. sulfurreducens. It has been suggested that filaments comprised of OmcS, rather than e-pili, are the predominant conductive filaments expressed by G. sulfurreducens. However, the results presented in this manuscript, along with multiple other lines of evidence, indicate that OmcS filaments cannot be the primary conductive protein nanowires expressed by G. sulfurreducens.
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Structure of Geobacter pili reveals secretory rather than nanowire behaviour. Nature 2021; 597:430-434. [PMID: 34471289 PMCID: PMC9127704 DOI: 10.1038/s41586-021-03857-w] [Citation(s) in RCA: 86] [Impact Index Per Article: 28.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2020] [Accepted: 07/28/2021] [Indexed: 02/07/2023]
Abstract
Extracellular electron transfer by Geobacter species through surface appendages known as microbial nanowires1 is important in a range of globally important environmental phenomena2, as well as for applications in bio-remediation, bioenergy, biofuels and bioelectronics. Since 2005, these nanowires have been thought to be type 4 pili composed solely of the PilA-N protein1. However, previous structural analyses have demonstrated that, during extracellular electron transfer, cells do not produce pili but rather nanowires made up of the cytochromes OmcS2,3 and OmcZ4. Here we show that Geobacter sulfurreducens binds PilA-N to PilA-C to assemble heterodimeric pili, which remain periplasmic under nanowire-producing conditions that require extracellular electron transfer5. Cryo-electron microscopy revealed that C-terminal residues of PilA-N stabilize its copolymerization with PilA-C (to form PilA-N-C) through electrostatic and hydrophobic interactions that position PilA-C along the outer surface of the filament. PilA-N-C filaments lack π-stacking of aromatic side chains and show a conductivity that is 20,000-fold lower than that of OmcZ nanowires. In contrast with surface-displayed type 4 pili, PilA-N-C filaments show structure, function and localization akin to those of type 2 secretion pseudopili6. The secretion of OmcS and OmcZ nanowires is lost when pilA-N is deleted and restored when PilA-N-C filaments are reconstituted. The substitution of pilA-N with the type 4 pili of other microorganisms also causes a loss of secretion of OmcZ nanowires. As all major phyla of prokaryotes use systems similar to type 4 pili, this nanowire translocation machinery may have a widespread effect in identifying the evolution and prevalence of diverse electron-transferring microorganisms and in determining nanowire assembly architecture for designing synthetic protein nanowires.
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Liu X, Walker DJF, Nonnenmann SS, Sun D, Lovley DR. Direct Observation of Electrically Conductive Pili Emanating from Geobacter sulfurreducens. mBio 2021; 12:e0220921. [PMID: 34465020 PMCID: PMC8406130 DOI: 10.1128/mbio.02209-21] [Citation(s) in RCA: 32] [Impact Index Per Article: 10.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/26/2021] [Accepted: 08/02/2021] [Indexed: 11/20/2022] Open
Abstract
Geobacter sulfurreducens is a model microbe for elucidating the mechanisms for extracellular electron transfer in several biogeochemical cycles, bioelectrochemical applications, and microbial metal corrosion. Multiple lines of evidence previously suggested that electrically conductive pili (e-pili) are an essential conduit for long-range extracellular electron transport in G. sulfurreducens. However, it has recently been reported that G. sulfurreducens does not express e-pili and that filaments comprised of multi-heme c-type cytochromes are responsible for long-range electron transport. This possibility was directly investigated by examining cells, rather than filament preparations, with atomic force microscopy. Approximately 90% of the filaments emanating from wild-type cells had a diameter (3 nm) and conductance consistent with previous reports of e-pili harvested from G. sulfurreducens or heterologously expressed in Escherichia coli from the G. sulfurreducens pilin gene. The remaining 10% of filaments had a morphology consistent with filaments comprised of the c-type cytochrome OmcS. A strain expressing a modified pilin gene designed to yield poorly conductive pili expressed 90% filaments with a 3-nm diameter, but greatly reduced conductance, further indicating that the 3-nm diameter conductive filaments in the wild-type strain were e-pili. A strain in which genes for five of the most abundant outer-surface c-type cytochromes, including OmcS, were deleted yielded only 3-nm-diameter filaments with the same conductance as in the wild type. These results demonstrate that e-pili are the most abundant conductive filaments expressed by G. sulfurreducens, consistent with previous functional studies demonstrating the need for e-pili for long-range extracellular electron transfer. IMPORTANCE Electroactive microbes have significant environmental impacts, as well as applications in bioenergy and bioremediation. The composition, function, and even existence of electrically conductive pili (e-pili) has been one of the most contentious areas of investigation in electromicrobiology, in part because e-pili offer a mechanism for long-range electron transport that does not involve the metal cofactors common in much of biological electron transport. This study demonstrates that e-pili are abundant filaments emanating from Geobacter sulfurreducens, which serves as a model for long-range extracellular electron transfer in direct interspecies electron transfer, dissimilatory metal reduction, microbe-electrode exchange, and corrosion caused by direct electron uptake from Fe(0). The methods described in this study provide a simple strategy for evaluating the distribution of conductive filaments throughout the microbial world with an approach that avoids artifactual production and/or enrichment of filaments that may not be physiologically relevant.
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Affiliation(s)
- Xinying Liu
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts, USA
- College of Environmental Science and Engineering, Beijing Forestry University, Beijing, China
| | - David J. F. Walker
- Department of Molecular Biosciences, University of Texas at Austin, Austin, Texas, USA
| | - Stephen S. Nonnenmann
- Institute for Applied Life Sciences, university of Massachusetts—Amherst, Amherst, Massachusetts, USA
- Department of Mechanical and Industrial Engineering, University of Massachusetts—Amherst, Amherst, Massachusetts, USA
| | - Dezhi Sun
- College of Environmental Science and Engineering, Beijing Forestry University, Beijing, China
| | - Derek R. Lovley
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts, USA
- Institute for Applied Life Sciences, university of Massachusetts—Amherst, Amherst, Massachusetts, USA
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Lovley DR, Holmes DE. Electromicrobiology: the ecophysiology of phylogenetically diverse electroactive microorganisms. Nat Rev Microbiol 2021; 20:5-19. [PMID: 34316046 DOI: 10.1038/s41579-021-00597-6] [Citation(s) in RCA: 176] [Impact Index Per Article: 58.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 06/16/2021] [Indexed: 02/03/2023]
Abstract
Electroactive microorganisms markedly affect many environments in which they establish outer-surface electrical contacts with other cells and minerals or reduce soluble extracellular redox-active molecules such as flavins and humic substances. A growing body of research emphasizes their broad phylogenetic diversity and shows that these microorganisms have key roles in multiple biogeochemical cycles, as well as the microbiome of the gut, anaerobic waste digesters and metal corrosion. Diverse bacteria and archaea have independently evolved cytochrome-based strategies for electron exchange between the outer cell surface and the cell interior, but cytochrome-free mechanisms are also prevalent. Electrically conductive protein filaments, soluble electron shuttles and non-biological conductive materials can substantially extend the electronic reach of microorganisms beyond the surface of the cell. The growing appreciation of the diversity of electroactive microorganisms and their unique electronic capabilities is leading to a broad range of applications.
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Affiliation(s)
- Derek R Lovley
- Electrobiomaterials Institute, Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang, China. .,Department of Microbiology, University of Massachusetts, Amherst, MA, USA. .,Institute for Applied Life Sciences (IALS), University of Massachusetts, Amherst, MA, USA.
| | - Dawn E Holmes
- Department of Microbiology, University of Massachusetts, Amherst, MA, USA.,Institute for Applied Life Sciences (IALS), University of Massachusetts, Amherst, MA, USA.,Department of Physical and Biological Sciences, Western New England University, Springfield, MA, USA
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Liu J, Liu X, Ding H, Ren G, Sun Y, Liu Y, Ji X, Ma LZ, Li Y, Lu A. Enhanced mechanism of extracellular electron transfer between semiconducting minerals anatase and Pseudomonas aeruginosa PAO1 in euphotic zone. Bioelectrochemistry 2021; 141:107849. [PMID: 34098461 DOI: 10.1016/j.bioelechem.2021.107849] [Citation(s) in RCA: 4] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2021] [Revised: 04/24/2021] [Accepted: 05/24/2021] [Indexed: 11/25/2022]
Abstract
Focusing the marine euphotic zone, which is the pivotal region for interaction of solar light-mineral-microorganism and the elements cycle, we have conducted the research on the mechanism of semiconducting minerals promoting extracellular electron transfer with microorganisms in depth. Therein, anatase which is one of the most representative semiconducting minerals in marine euphotic zone was selected. The mineralogical characterization of anatase was identified by ESEM, AFM, EDS, Raman, XRD, and its semiconducting characteristics was determined by UV-Vis and Mott-Schottky plots. Determined by the electrochemical measurement of I-t curves, the photocurrent density of anatase was more prominent than dark current density. Pseudomonas aeruginosa PAO1 was widely distributed in the euphotic zone, and its mutants of operons deficient in biosynthesis pyocyanin (Δphz1Δphz2) and pili deficient (ΔpilA) were employed in this study. I-t curves indicated that both direct and indirect extracellular electron transfer processes occurred between anatase and PAO1. The indirect electron transfer depending on pyocyanin secreted by PAO1 was the main electron transfer mode. This work demonstrated the light-driven extracellular electron transfer and further revealed the photo-catalyzed mechanisms between anatase and PAO1 in marine euphotic zone.
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Affiliation(s)
- Jia Liu
- The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing Key Laboratory of Mineral Environmental Function, Beijing 100871, China
| | - Xi Liu
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China
| | - Hongrui Ding
- The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing Key Laboratory of Mineral Environmental Function, Beijing 100871, China.
| | | | - Yuan Sun
- The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing Key Laboratory of Mineral Environmental Function, Beijing 100871, China
| | - Ying Liu
- The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing Key Laboratory of Mineral Environmental Function, Beijing 100871, China
| | - Xiang Ji
- The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing Key Laboratory of Mineral Environmental Function, Beijing 100871, China
| | - Luyan Z Ma
- State Key Laboratory of Microbial Resources, Institute of Microbiology, Chinese Academy of Sciences, Beijing 100101, China; University of the Chinese Academy of Sciences, Beijing 100049, China
| | - Yan Li
- The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing Key Laboratory of Mineral Environmental Function, Beijing 100871, China
| | - Anhuai Lu
- The Key Laboratory of Orogenic Belts and Crustal Evolution, School of Earth and Space Sciences, Peking University, Beijing Key Laboratory of Mineral Environmental Function, Beijing 100871, China.
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31
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Dissecting the Structural and Conductive Functions of Nanowires in Geobacter sulfurreducens Electroactive Biofilms. mBio 2021; 13:e0382221. [PMID: 35164556 PMCID: PMC8844916 DOI: 10.1128/mbio.03822-21] [Citation(s) in RCA: 10] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Conductive nanowires are thought to contribute to long-range electron transfer (LET) in Geobacter sulfurreducens anode biofilms. Three types of nanowires have been identified: pili, OmcS, and OmcZ. Previous studies highlighted their conductive function in anode biofilms, yet a structural function also has to be considered. We present here a comprehensive analysis of the function of nanowires in LET by inhibiting the expression of each nanowire. Meanwhile, flagella with poor conductivity were expressed to recover the structural function but not the conductive function of nanowires in the corresponding nanowire mutant strain. The results demonstrated that pili played a structural but not a conductive function in supporting biofilm formation. In contrast, the OmcS nanowire played a conductive but not a structural function in facilitating electron transfer in the biofilm. The OmcZ nanowire played both a structural and a conductive function to contribute to current generation. Expression of the poorly conductive flagellum was shown to enhance biofilm formation, subsequently increasing current generation. These data support a model in which multiheme cytochromes facilitate long-distance electron transfer in G. sulfurreducens biofilms. Our findings also suggest that the formation of a thicker biofilm, which contributed to a higher current generation by G. sulfurreducens, was confined by the biofilm formation deficiency, and this has applications in microbial electrochemical systems. IMPORTANCE The low power generation of microbial fuel cells limits their utility. Many factors can affect power generation, including inefficient electron transfer in the anode biofilm. Thus, understanding the mechanism(s) of electron transfer provides a pathway for increasing the power density of microbial fuel cells. Geobacter sulfurreducens was shown to form a thick biofilm on the anode. Cells far away from the anode reduce the anode through long-range electron transfer. Based on their conductive properties, three types of nanowires have been hypothesized to directly facilitate long-range electron transfer: pili, OmcS, and OmcZ nanowires. However, their structural contributions to electron transfer in anode biofilm have not been elucidated. Based on studies of mutants lacking one or more of these facilitators, our results support a cytochrome-mediated electron transfer process in Geobacter biofilms and highlight the structural contribution of nanowires in anode biofilm formation, which contributes to biofilm formation and current generation, thereby providing a strategy to increase current generation.
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Kang HJ, Lee SH, Lim TG, Park JH, Kim B, Buffière P, Park HD. Recent advances in methanogenesis through direct interspecies electron transfer via conductive materials: A molecular microbiological perspective. BIORESOURCE TECHNOLOGY 2021; 322:124587. [PMID: 33358582 DOI: 10.1016/j.biortech.2020.124587] [Citation(s) in RCA: 29] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/30/2020] [Revised: 12/15/2020] [Accepted: 12/16/2020] [Indexed: 05/28/2023]
Abstract
Conductive materials can serve as biocatalysts during direct interspecies electron transfer for methanogenesis in anaerobic reactors. However, the mechanism promoting direct interspecies electron transfer in anaerobic reactors, particularly under environments in which diverse substrates and microorganisms coexist, remains to be elucidated from a scientific or an engineering point of view. Currently, many molecular microbiological approaches are employed to understand the fundamentals of this phenomenon. Here, the direct interspecies electron transfer mechanisms and relevant microorganisms identified to date using molecular microbiological methods were critically reviewed. Moreover, molecular microbiological methods for direct interspecies electron transfer used in previous studies and important findings thus revealed were analyzed. This review will help us better understand the phenomena of direct interspecies electron transfer using conductive materials and offer a framework for future molecular microbiological studies.
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Affiliation(s)
- Hyun-Jin Kang
- School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, South Korea
| | - Sang-Hoon Lee
- School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, South Korea
| | - Tae-Guen Lim
- School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, South Korea
| | - Jeong-Hoon Park
- Sustainable Technology and Wellness R&D Group, Korea Institute of Industrial Technology (KITECH), Jeju-si, South Korea
| | - Boram Kim
- DEEP Laboratory, Université de Lyon, INSA Lyon, Lyon, France
| | - Pierre Buffière
- DEEP Laboratory, Université de Lyon, INSA Lyon, Lyon, France
| | - Hee-Deung Park
- School of Civil, Environmental and Architectural Engineering, Korea University, Seoul, South Korea.
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33
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Lovley DR, Yao J. Intrinsically Conductive Microbial Nanowires for 'Green' Electronics with Novel Functions. Trends Biotechnol 2021; 39:940-952. [PMID: 33419586 DOI: 10.1016/j.tibtech.2020.12.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 11.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/03/2020] [Revised: 12/04/2020] [Accepted: 12/07/2020] [Indexed: 10/22/2022]
Abstract
Intrinsically conductive protein nanowires, microbially produced from inexpensive, renewable feedstocks, are a sustainable alternative to traditional nanowire electronic materials, which require high energy inputs and hazardous conditions/chemicals for fabrication and can be highly toxic. Pilin-based nanowires can be tailored for specific functions via the design of synthetic pilin genes to tune wire conductivity or introduce novel functionalities. Other microbially produced nanowire options for electronics may include cytochrome wires, curli fibers, and the conductive fibers of cable bacteria. Proof-of-concept protein nanowire electronics that have been successfully demonstrated include biomedical sensors, neuromorphic devices, and a device that generates electricity from ambient humidity. Further development of applications will require interdisciplinary teams of engineers, biophysicists, and synthetic biologists.
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Affiliation(s)
- Derek R Lovley
- Electrobiomaterials Institute, Key Laboratory for Anisotropy and Texture of Materials (Ministry of Education), Northeastern University, Shenyang 110819, China; Department of Microbiology, University of Massachusetts, Amherst, MA, USA; Institute for Applied Life Sciences (IALS), University of Massachusetts, Amherst, MA, USA.
| | - Jun Yao
- Institute for Applied Life Sciences (IALS), University of Massachusetts, Amherst, MA, USA; Department of Electrical and Computer Engineering, University of Massachusetts, Amherst, MA, USA; Department of Biomedical Engineering, University of Massachusetts, Amherst, MA, USA
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34
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Lovley DR, Holmes DE. Protein Nanowires: the Electrification of the Microbial World and Maybe Our Own. J Bacteriol 2020; 202:e00331-20. [PMID: 32747429 PMCID: PMC7515249 DOI: 10.1128/jb.00331-20] [Citation(s) in RCA: 31] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
Electrically conductive protein nanowires appear to be widespread in the microbial world and are a revolutionary "green" material for the fabrication of electronic devices. Electrically conductive pili (e-pili) assembled from type IV pilin monomers have independently evolved multiple times in microbial history as have electrically conductive archaella (e-archaella) assembled from homologous archaellin monomers. A role for e-pili in long-range (micrometer) extracellular electron transport has been demonstrated in some microbes. The surprising finding of e-pili in syntrophic bacteria and the role of e-pili as conduits for direct interspecies electron transfer have necessitated a reassessment of routes for electron flux in important methanogenic environments, such as anaerobic digesters and terrestrial wetlands. Pilin monomers similar to those found in e-pili may also be a major building block of the conductive "cables" that transport electrons over centimeter distances through continuous filaments of cable bacteria consisting of a thousand cells or more. Protein nanowires harvested from microbes have many functional and sustainability advantages over traditional nanowire materials and have already yielded novel electronic devices for sustainable electricity production, neuromorphic memory, and sensing. e-pili can be mass produced with an Escherichia coli chassis, providing a ready source of material for electronics as well as for studies on the basic mechanisms for long-range electron transport along protein nanowires. Continued exploration is required to better understand the electrification of microbial communities with microbial nanowires and to expand the "green toolbox" of sustainable materials for wiring and powering the emerging "Internet of things."
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Affiliation(s)
- Derek R Lovley
- Department of Microbiology, University of Massachusetts, Amherst, Massachusetts, USA
- Institute of Applied Life Sciences, University of Massachusetts, Amherst, Massachusetts, USA
| | - Dawn E Holmes
- Department of Microbiology, University of Massachusetts, Amherst, Massachusetts, USA
- Department of Physical and Biological Sciences, Western New England University, Springfield, Massachusetts, USA
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35
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Wei W, Plymale A, Zhu Z, Ma X, Liu F, Yu XY. In Vivo Molecular Insights into Syntrophic Geobacter Aggregates. Anal Chem 2020; 92:10402-10411. [PMID: 32614167 DOI: 10.1021/acs.analchem.0c00653] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Direct interspecies electron transfer (DIET) has been considered as a novel and highly efficient strategy in both natural anaerobic environments and artificial microbial fuel cells. A syntrophic model consisting of Geobacter metallireducens and Geobacter sulfurreducens was studied in this work. We conducted in vivo molecular mapping of the outer surface of the syntrophic community as the interface of nutrients and energy exchange. System for Analysis at the Liquid Vacuum Interface combined with time-of-flight secondary ion mass spectrometry was employed to capture the molecular distribution of syntrophic Geobacter communities in the living and hydrated state. Principal component analysis with selected peaks revealed that syntrophic Geobacter aggregates were well differentiated from other control samples, including syntrophic planktonic cells, pure cultured planktonic cells, and single population biofilms. Our in vivo imaging indicated that a unique molecular surface was formed. Specifically, aromatic amino acids, phosphatidylethanolamine components, and large water clusters were identified as key components that favored the DIET of syntrophic Geobacter aggregates. Moreover, the molecular changes in depths of the Geobacter aggregates were captured using dynamic depth profiling. Our findings shed new light on the interface components supporting electron transfer in syntrophic communities based on in vivo molecular imaging.
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Affiliation(s)
- Wenchao Wei
- Key Laboratory of Coastal Biology and Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, Shandong 264003, P. R. China.,Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States.,University of Chinese Academy of Sciences, Beijing 100049, P. R. China
| | - Andrew Plymale
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Zihua Zhu
- Environmental and Molecular Science Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
| | - Xiang Ma
- Department of Chemistry, Grand View University, Des Moines, Iowa 50316, United States
| | - Fanghua Liu
- Key Laboratory of Coastal Biology and Utilization, Yantai Institute of Coastal Zone Research, Chinese Academy of Sciences, Yantai, Shandong 264003, P. R. China
| | - Xiao-Ying Yu
- Energy and Environment Directorate, Pacific Northwest National Laboratory, Richland, Washington 99352, United States
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36
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Ueki T, Walker DJF, Woodard TL, Nevin KP, Nonnenmann SS, Lovley DR. An Escherichia coli Chassis for Production of Electrically Conductive Protein Nanowires. ACS Synth Biol 2020; 9:647-654. [PMID: 32125829 DOI: 10.1021/acssynbio.9b00506] [Citation(s) in RCA: 39] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Geobacter sulfurreducens' pilin-based electrically conductive protein nanowires (e-PNs) are a revolutionary electronic material. They offer novel options for electronic sensing applications and have the remarkable ability to harvest electrical energy from atmospheric humidity. However, technical constraints limit mass cultivation and genetic manipulation of G. sulfurreducens. Therefore, we designed a strain of Escherichia coli to express e-PNs by introducing a plasmid that contained an inducible operon with E. coli genes for type IV pili biogenesis machinery and a synthetic gene designed to yield a peptide monomer that could be assembled into e-PNs. The e-PNs expressed in E. coli and harvested with a simple filtration method had the same diameter (3 nm) and conductance as e-PNs expressed in G. sulfurreducens. These results, coupled with the robustness of E. coli for mass cultivation and the extensive E. coli toolbox for genetic manipulation, greatly expand the opportunities for large-scale fabrication of novel e-PNs.
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Affiliation(s)
- Toshiyuki Ueki
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
- Institute for Applied Life Sciences, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
| | - David J. F. Walker
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
- Institute for Applied Life Sciences, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
| | - Trevor L. Woodard
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
| | - Kelly P. Nevin
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
| | - Stephen S. Nonnenmann
- Institute for Applied Life Sciences, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
- Department of Mechanical and Industrial Engineering, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
| | - Derek R. Lovley
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
- Institute for Applied Life Sciences, University of Massachusetts-Amherst, Amherst, Massachusetts 01003, United States
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37
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Bray MS, Wu J, Padilla CC, Stewart FJ, Fowle DA, Henny C, Simister RL, Thompson KJ, Crowe SA, Glass JB. Phylogenetic and structural diversity of aromatically dense pili from environmental metagenomes. ENVIRONMENTAL MICROBIOLOGY REPORTS 2020; 12:49-57. [PMID: 31701641 PMCID: PMC7779115 DOI: 10.1111/1758-2229.12809] [Citation(s) in RCA: 14] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 10/14/2019] [Accepted: 11/03/2019] [Indexed: 06/10/2023]
Abstract
Electroactive type IV pili, or e-pili, are used by some microbial species for extracellular electron transfer. Recent studies suggest that e-pili may be more phylogenetically and structurally diverse than previously assumed. Here, we used updated aromatic density thresholds (≥9.8% aromatic amino acids, ≤22-aa aromatic gaps and aromatic amino acids at residues 1, 24, 27, 50 and/or 51, and 32 and/or 57) to search for putative e-pilin genes in metagenomes from diverse ecosystems with active microbial metal cycling. Environmental putative e-pilins were diverse in length and phylogeny, and included truncated e-pilins in Geobacter spp., as well as longer putative e-pilins in Fe(II)-oxidizing Betaproteobacteria and Zetaproteobacteria.
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Affiliation(s)
- Marcus S. Bray
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - Jieying Wu
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - Cory C. Padilla
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - Frank J. Stewart
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
| | - David A. Fowle
- Department of Geology, University of Kansas, Lawrence, KS, USA
| | - Cynthia Henny
- Research Center for Limnology, Indonesian Institute of Sciences, Cibinong, Indonesia
| | - Rachel L. Simister
- Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada
| | - Katharine J. Thompson
- Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada
| | - Sean A. Crowe
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- Department of Earth, Ocean, and Atmospheric Sciences, University of British Columbia, Vancouver, BC, Canada
- Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC, Canada
- Division of Earth and Planetary Sciences, School of Biological Sciences, and Swire Institute of Marine Science, The University of Hong Kong, Hong Kong
| | - Jennifer B. Glass
- School of Biological Sciences, Georgia Institute of Technology, Atlanta, GA, USA
- School of Earth and Atmospheric Sciences, Georgia Institute of Technology, Atlanta, GA, USA
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38
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Walker DJF, Nevin KP, Holmes DE, Rotaru AE, Ward JE, Woodard TL, Zhu J, Ueki T, Nonnenmann SS, McInerney MJ, Lovley DR. Syntrophus conductive pili demonstrate that common hydrogen-donating syntrophs can have a direct electron transfer option. ISME JOURNAL 2020; 14:837-846. [PMID: 31896792 DOI: 10.1038/s41396-019-0575-9] [Citation(s) in RCA: 72] [Impact Index Per Article: 18.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/01/2019] [Revised: 12/02/2019] [Accepted: 12/16/2019] [Indexed: 11/09/2022]
Abstract
Syntrophic interspecies electron exchange is essential for the stable functioning of diverse anaerobic microbial communities. Hydrogen/formate interspecies electron transfer (HFIT), in which H2 and/or formate function as diffusible electron carriers, has been considered to be the primary mechanism for electron transfer because most common syntrophs were thought to lack biochemical components, such as electrically conductive pili (e-pili), necessary for direct interspecies electron transfer (DIET). Here we report that Syntrophus aciditrophicus, one of the most intensively studied microbial models for HFIT, produces e-pili and can grow via DIET. Heterologous expression of the putative S. aciditrophicus type IV pilin gene in Geobacter sulfurreducens yielded conductive pili of the same diameter (4 nm) and conductance of the native S. aciditrophicus pili and enabled long-range electron transport in G. sulfurreducens. S. aciditrophicus lacked abundant c-type cytochromes often associated with DIET. Pilin genes likely to yield e-pili were found in other genera of hydrogen/formate-producing syntrophs. The finding that DIET is a likely option for diverse syntrophs that are abundant in many anaerobic environments necessitates a reexamination of the paradigm that HFIT is the predominant mechanism for syntrophic electron exchange within anaerobic microbial communities of biogeochemical and practical significance.
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Affiliation(s)
- David J F Walker
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA.,Institute for Applied Life Sciences, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Kelly P Nevin
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Dawn E Holmes
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA.,Department of Physical and Biological Science, Western New England University, Springfield, MA, USA
| | - Amelia-Elena Rotaru
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA.,Department of Biology, University of Southern Denmark, Odense, Denmark
| | - Joy E Ward
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Trevor L Woodard
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Jiaxin Zhu
- Department of Mechanical and Industrial Engineering, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Toshiyuki Ueki
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Stephen S Nonnenmann
- Institute for Applied Life Sciences, University of Massachusetts-Amherst, Amherst, MA, USA.,Department of Mechanical and Industrial Engineering, University of Massachusetts-Amherst, Amherst, MA, USA
| | - Michael J McInerney
- Department of Microbiology and Plant Biology, University of Oklahoma, Norman, OK, USA
| | - Derek R Lovley
- Department of Microbiology, University of Massachusetts-Amherst, Amherst, MA, USA. .,Institute for Applied Life Sciences, University of Massachusetts-Amherst, Amherst, MA, USA.
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Liu X, Ye Y, Xiao K, Rensing C, Zhou S. Molecular evidence for the adaptive evolution of Geobacter sulfurreducens to perform dissimilatory iron reduction in natural environments. Mol Microbiol 2019; 113:783-793. [PMID: 31872462 DOI: 10.1111/mmi.14443] [Citation(s) in RCA: 17] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/24/2019] [Revised: 12/17/2019] [Accepted: 12/19/2019] [Indexed: 02/05/2023]
Abstract
The electrically conductive pili (e-pili) of Geobacter species enable extracellular electron transfer to insoluble metallic minerals, electrodes and other microbial species, which confers biogeochemical significance and global prevalence on Geobacter in diverse anaerobic environments. E-pili are constructed by truncated PilA which is considered to have evolved from full-length pilin by gene fission under positive evolutionary selection. However, this hypothesis is based on phylogenetic analysis and has not yet been experimentally confirmed. Here, we reconstructed an ancestral strain of G. sulfurreducens (designated COMB) carrying full-length PilA by combining genes GSU1496 and GSU1497. The results demonstrated that strain COMB expressed and assembled the full-length fused PilA and exhibited an outer membrane c-type cytochrome profile similar to the wild-type strain. Surprisingly, the generated COMB-pili were also conductive, indicating the evolution of truncated PilA did not occur for conductivity. Moreover, strain COMB minimally reduced Fe(III) oxides but maintained its ability to respire electrodes, demonstrating the truncation of pilin enables iron respiration. This study provides the first experimental evidence that the truncation of pilin in Geobacter species confers adaption to Fe(III)-mineral-mediated selective pressures, and suggests an evolutionary event during which the separation of the GSU1497 gene helped Geobacter survive and thrive in natural environments.
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Affiliation(s)
- Xing Liu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Yin Ye
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Ke Xiao
- State Key Laboratory of Bioelectronics, Southeast University, Nanjing, China
| | - Christopher Rensing
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
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40
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Xu H, Chang J, Wang H, Liu Y, Zhang X, Liang P, Huang X. Enhancing direct interspecies electron transfer in syntrophic-methanogenic associations with (semi)conductive iron oxides: Effects and mechanisms. THE SCIENCE OF THE TOTAL ENVIRONMENT 2019; 695:133876. [PMID: 31756846 DOI: 10.1016/j.scitotenv.2019.133876] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2019] [Revised: 08/09/2019] [Accepted: 08/09/2019] [Indexed: 06/10/2023]
Abstract
Anaerobic digestion is an effective biological treatment process that produces methane by degrading organic compounds in waste/wastewater. It is a complicated microbial process by metabolic interactions among different types of microorganisms. In this process, efficient interspecies electron transfer between secondary fermenting bacteria and methanogens is the critical process for fast and effective methanogenesis. In syntrophic metabolism, hydrogen or formate has been considered as the conventional electron carrier transferring electrons from secondary fermenting bacteria to hydrogenotrophic methanogens. Recently, direct interspecies electron transfer (DIET) without the involvement of dissolved redox mediators is arousing great concerns and has been regarded as a more efficient and thermodynamically favorable interspecies electron transfer pathway for methanogenesis. Interspecies electron exchange through DIET is accomplished via the membrane-bound cytochromes or conductive pili. Several kinds of exogenously-added conductive or semiconductive iron oxides have been discovered to greatly enhance anaerobic methanogenesis through promoting DIET. Different (semi)conductive iron oxides give a boost to DIET through different mechanisms based on the physicochemical properties of the iron oxides and the reciprocal interactions between iron oxides and functional microorganisms. In this review, the current understanding of interspecies electron transfer in syntrophic-methanogenic consortions is summarized, the effects and deep-rooted mechanisms of (semi)conductive iron oxides on methanogenesis and DIET are discussed, and possible future perspectives and development directions are suggested for DIET via (semi)conductive iron oxides in anaerobic digestion.
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Affiliation(s)
- Hui Xu
- State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment, Tsinghua University, Beijing 100084, China
| | - Jiali Chang
- State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment, Tsinghua University, Beijing 100084, China
| | - Han Wang
- State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment, Tsinghua University, Beijing 100084, China
| | - Yancheng Liu
- State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment, Tsinghua University, Beijing 100084, China
| | - Xiaoyuan Zhang
- State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment, Tsinghua University, Beijing 100084, China
| | - Peng Liang
- State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment, Tsinghua University, Beijing 100084, China
| | - Xia Huang
- State Key Joint Laboratory of Environment Simulation and Pollution Control School of Environment, Tsinghua University, Beijing 100084, China.
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41
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Liu X, Zhuo S, Jing X, Yuan Y, Rensing C, Zhou S. Flagella act as Geobacter biofilm scaffolds to stabilize biofilm and facilitate extracellular electron transfer. Biosens Bioelectron 2019; 146:111748. [DOI: 10.1016/j.bios.2019.111748] [Citation(s) in RCA: 40] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2019] [Revised: 09/22/2019] [Accepted: 09/30/2019] [Indexed: 11/24/2022]
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42
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Huang L, Liu X, Ye Y, Chen M, Zhou S. Evidence for the coexistence of direct and riboflavin-mediated interspecies electron transfer in Geobacter co-culture. Environ Microbiol 2019; 22:243-254. [PMID: 31657092 DOI: 10.1111/1462-2920.14842] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/25/2019] [Revised: 10/20/2019] [Accepted: 10/23/2019] [Indexed: 11/30/2022]
Abstract
Geobacter species can secrete free redox-active flavins, but the role of these flavins in the interspecies electron transfer (IET) of Geobacter direct interspecies electron transfer (DIET) co-culture is unknown. Here, we report the presence of a new riboflavin-mediated interspecies electron transfer (RMIET) process in a traditional Geobacter DIET co-culture; in this process, riboflavin contributes to IET by acting as a free-form electron shuttle between free Geobacter species and serving as a bound cofactor of some cytochromes in Geobacter co-culture aggregates. Multiple lines of evidence indicate that RMIET facilitates the primary initiation of syntrophic growth between Geobacter species before establishing the DIET co-culture and provides additional ways alongside the DIET to transfer electrons to achieve electric syntrophy between Geobacter species. Redox kinetic analysis of riboflavin on either Geobacter species demonstrated that the Gmet_2896 cytochrome acts as the key riboflavin reduction site, while riboflavin oxidation by Geobacter sulfurreducens is the rate-limiting step in RMIET, and the RMIET makes only a minor contribution to IET in Geobacter DIET co-culture. The discovery of a new RMIET process in Geobacter DIET co-culture suggests the complexity of IET in syntrophic bacterial communities and provides suggestions for the careful examination of the IET of other syntrophic co-cultures.
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Affiliation(s)
- Lingyan Huang
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Xing Liu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Yin Ye
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Man Chen
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
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Abstract
The study of electrically conductive protein nanowires in Geobacter sulfurreducens has led to new concepts for long-range extracellular electron transport, as well as for the development of sustainable conductive materials and electronic devices with novel functions. Until recently, electrically conductive pili (e-pili), assembled from the PilA pilin monomer, were the only known Geobacter protein nanowires. However, filaments comprised of the multi-heme c-type cytochrome, OmcS, are present in some preparations of G. sulfurreducens outer-surface proteins. The purpose of this review is to evaluate the available evidence on the in vivo expression of e-pili and OmcS filaments and their biological function. Abundant literature demonstrates that G. sulfurreducens expresses e-pili, which are required for long-range electron transport to Fe (III) oxides and through conductive biofilms. In contrast, there is no definitive evidence yet that wild-type G. sulfurreducens express long filaments of OmcS extending from the cells, and deleting the gene for OmcS actually increases biofilm conductivity. The literature does not support the concern that many previous studies on e-pili were mistakenly studying OmcS filaments. For example, heterologous expression of the aromatic-rich pilin monomer of Geobacter metallireducens in G. sulfurreducens increases the conductivity of individual nanowires more than 5,000-fold, whereas expression of an aromatic-poor pilin reduced conductivity more than 1,000-fold. This more than million-fold range in nanowire conductivity was achieved while maintaining the 3-nm diameter characteristic of e-pili. Purification methods that eliminate all traces of OmcS yield highly conductive e-pili, as does heterologous expression of the e-pilin monomer in microbes that do not produce OmcS or any other outer-surface cytochromes. Future studies of G. sulfurreducens expression of protein nanowires need to be cognizant of the importance of maintaining environmentally relevant growth conditions because artificial laboratory culture conditions can rapidly select against e-pili expression. Principles derived from the study of e-pili have enabled identification of non-cytochrome protein nanowires in diverse bacteria and archaea. A similar search for cytochrome appendages is warranted. Both e-pili and OmcS filaments offer design options for the synthesis of protein-based "green" electronics, which may be the primary driving force for the study of these structures in the near future.
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Affiliation(s)
- Derek R. Lovley
- Department of Microbiology, Institute for Applied Life Sciences, University of Massachusetts, Amherst, MA, United States
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44
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Ueki T, Walker DJ, Tremblay PL, Nevin KP, Ward JE, Woodard TL, Nonnenmann SS, Lovley DR. Decorating the Outer Surface of Microbially Produced Protein Nanowires with Peptides. ACS Synth Biol 2019; 8:1809-1817. [PMID: 31298834 DOI: 10.1021/acssynbio.9b00131] [Citation(s) in RCA: 32] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The potential applications of electrically conductive protein nanowires (e-PNs) harvested from Geobacter sulfurreducens might be greatly expanded if the outer surface of the wires could be modified to confer novel sensing capabilities or to enhance binding to other materials. We developed a simple strategy for functionalizing e-PNs with surface-exposed peptides. The G. sulfurreducens gene for the monomer that assembles into e-PNs was modified to add peptide tags at the carboxyl terminus of the monomer. Strains of G. sulfurreducens were constructed that fabricated synthetic e-PNs with a six-histidine "His-tag" or both the His-tag and a nine-peptide "HA-tag" exposed on the outer surface. Addition of the peptide tags did not diminish e-PN conductivity. The abundance of HA-tag in e-PNs was controlled by placing expression of the gene for the synthetic monomer with the HA-tag under transcriptional regulation. These studies suggest broad possibilities for tailoring e-PN properties for diverse applications.
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Affiliation(s)
- Toshiyuki Ueki
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
- Institute for Applied Life Sciences, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
| | - David J.F. Walker
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
- Institute for Applied Life Sciences, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
| | - Pier-Luc Tremblay
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
| | - Kelly P. Nevin
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
| | - Joy E. Ward
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
| | - Trevor L. Woodard
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
| | - Stephen S. Nonnenmann
- Institute for Applied Life Sciences, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
- Department of Mechanical and Industrial Engineering, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
| | - Derek R. Lovley
- Department of Microbiology, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
- Institute for Applied Life Sciences, University of Massachusetts—Amherst, Amherst, Massachusetts 01003, United States
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45
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Electrochemical evidence for direct interspecies electron transfer between Geobacter sulfurreducens and Prosthecochloris aestuarii. Bioelectrochemistry 2019; 127:21-25. [DOI: 10.1016/j.bioelechem.2019.01.002] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2018] [Revised: 01/03/2019] [Accepted: 01/03/2019] [Indexed: 01/07/2023]
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46
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Liu X, Zhan J, Jing X, Zhou S, Lovley DR. A pilin chaperone required for the expression of electrically conductive
Geobacter sulfurreducens
pili. Environ Microbiol 2019; 21:2511-2522. [DOI: 10.1111/1462-2920.14638] [Citation(s) in RCA: 16] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2019] [Revised: 04/15/2019] [Accepted: 04/21/2019] [Indexed: 11/30/2022]
Affiliation(s)
- Xing Liu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and EnvironmentFujian Agriculture and Forestry University Fuzhou China
| | - Ji Zhan
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and EnvironmentFujian Agriculture and Forestry University Fuzhou China
| | - Xianyue Jing
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and EnvironmentFujian Agriculture and Forestry University Fuzhou China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and EnvironmentFujian Agriculture and Forestry University Fuzhou China
| | - Derek R. Lovley
- Department of MicrobiologyUniversity of Massachusetts Amherst Amherst MA USA
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47
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Lebedev N, Stroud RM, Yates MD, Tender LM. Spatially Resolved Chemical Analysis of Geobacter sulfurreducens Cell Surface. ACS NANO 2019; 13:4834-4842. [PMID: 30943001 DOI: 10.1021/acsnano.9b02032] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/09/2023]
Abstract
Geobacter sulfurreducens is of interest for the highest efficiency of power generation and extremely long extracellular electron transfer (EET) between the bacterium and electrodes. Despite more than 15 years of intensive molecular biological research, there is still no clear answer which molecules are responsible for these processes. In the present work, we look at the problem from another (atomic) perspective and identify the location and shape of the compounds that are known to be conductive, particularly those containing Fe atoms. By using highly sophisticated energy dispersive X-ray spectroscopy combined with high-angle annular dark-field transmission electron microscopy enabling detection, identification, and localization of chemical compounds on the surface at nearly atomic spatial resolution, we analyze Fe spatial distribution within the G. sulfurreducens community. We discover the presence of small Fe-containing particles on the surface of the bacterium cells. The size of the particles (diameter 5.6 nm) is highly reproducible and comparable with the size of a single protein. The particles cover about 2% of the cell surface, which is similar to that expected for molecular conductors responsible for electron transfer through the bacterium cell wall. We find that G. sulfurreducens filaments ("bacterial molecular wires") also contain Fe atoms in their bundles. We observe that the bacterium enable changing the distance between the Fe-containing bundles in the filaments from separated to attached (the latter is needed for the efficient electron transfer between the Fe-containing particles), depending on the bacterium metabolic activity and attachment to extracellular substrates. These results are consistent with the recently published research about the role of Fe atoms in protein molecular conductance ( Phys. Chem. Chem. Phys. , 2018 , 20 , 14072 - 14081 ) and show what type of Fe-containing particles are involved in the bacterial extracellular communication. They can be used for the design and construction of artificial biomolecular wires and bioinorganic interfaces.
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Affiliation(s)
- Nikolai Lebedev
- Center for Bio/Molecular Science and Engineering , U.S. Naval Research Laboratory , Washington , DC 20375 , United States
| | - Rhonda M Stroud
- Materials Science and Technology Division , U.S. Naval Research Laboratory , Washington , DC 20375 , United States
| | - Matthew D Yates
- Center for Bio/Molecular Science and Engineering , U.S. Naval Research Laboratory , Washington , DC 20375 , United States
| | - Leonard Martin Tender
- Center for Bio/Molecular Science and Engineering , U.S. Naval Research Laboratory , Washington , DC 20375 , United States
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48
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On-Line Raman Spectroscopic Study of Cytochromes' Redox State of Biofilms in Microbial Fuel Cells. Molecules 2019; 24:molecules24030646. [PMID: 30759821 PMCID: PMC6384720 DOI: 10.3390/molecules24030646] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/29/2018] [Revised: 02/07/2019] [Accepted: 02/09/2019] [Indexed: 11/17/2022] Open
Abstract
Bio-electrochemical systems such as microbial fuel cells and microbial electrosynthesis cells depend on efficient electron transfer between the microorganisms and the electrodes. Understanding the mechanisms and dynamics of the electron transfer is important in order to design more efficient reactors, as well as modifying microorganisms for enhanced electricity production. Geobacter are well known for their ability to form thick biofilms and transfer electrons to the surfaces of electrodes. Currently, there are not many “on-line” systems for monitoring the activity of the biofilm and the electron transfer process without harming the biofilm. Raman microscopy was shown to be capable of providing biochemical information, i.e., the redox state of C-type cytochromes, which is integral to external electron transfer, without harming the biofilm. In the current study, a custom 3D printed flow-through cuvette was used in order to analyze the oxidation state of the C-type cytochromes of suspended cultures of three Geobacter sulfurreducens strains (PCA, KN400 and ΔpilA). It was found that the oxidation state is a good indicator of the metabolic state of the cells. Furthermore, an anaerobic fluidic system enabling in situ Raman measurements was designed and applied successfully to monitor and characterize G. sulfurreducens biofilms during electricity generation, for both a wild strain, PCA, and a mutant, ΔS. The cytochrome redox state, monitored by the Raman peak areas, could be modulated by applying different poise voltages to the electrodes. This also correlated with the modulation of current transferred from the cytochromes to the electrode. The Raman peak area changed in a predictable and reversible manner, indicating that the system could be used for analyzing the oxidation state of the proteins responsible for the electron transfer process and the kinetics thereof in-situ.
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49
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Biological synthesis of high-conductive pili in aerobic bacterium Pseudomonas aeruginosa. Appl Microbiol Biotechnol 2018; 103:1535-1544. [PMID: 30523372 DOI: 10.1007/s00253-018-9484-5] [Citation(s) in RCA: 40] [Impact Index Per Article: 6.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2018] [Accepted: 10/22/2018] [Indexed: 10/27/2022]
Abstract
Bioelectrical nanowires as ecomaterials have great potential on environmental applications. A wide range of bacteria can express type IV pili (T4P), which are long protein fibers assembled from PilA. The T4P of Geobacter sulfurreducens are well known as "microbial nanowires," yet T4P of Pseudomonas aeruginosa (PaT4P) was believed to be poorly conductive. P. aeruginosa is an aerobic and electrochemically active bacterium. Its T4P have been known to be responsible for surface attachment, twitching motility and biofilm formation. Here, we show that PaT4P can be highly conductive while assembled by a truncated P. aeruginosa PilA (PaPilA) containing only N-terminus 61 amino acids. Furthermore, increasing the number of aromatic amino acids in the PaPilA1-61 significantly enhances the conductivity of pili and the bioelectricity output of P. aeruginosa in microbial fuel cell system, suggesting a potential application of PaT4P as a conductive nanomaterial. The N-terminal region of PilA from diverse eubacteria is highly conserved, implying a general way to synthesize highly conductive microbial nanowires and to increase the bioelectricity output of microbial fuel cell.
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50
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Huang L, Tang J, Chen M, Liu X, Zhou S. Two Modes of Riboflavin-Mediated Extracellular Electron Transfer in Geobacter uraniireducens. Front Microbiol 2018; 9:2886. [PMID: 30538691 PMCID: PMC6277576 DOI: 10.3389/fmicb.2018.02886] [Citation(s) in RCA: 25] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2018] [Accepted: 11/12/2018] [Indexed: 12/31/2022] Open
Abstract
Anaerobes respire extracellular electron acceptors by extracellular electron transfer (EET). It is widely recognized that flavins can act as electron shuttles to facilitate this process. Flavin synthesis genes are widely distributed in Geobacter species. However, the functions of flavins in the EET of Geobacter species are unclear. Here, we demonstrate that G. uraniireducens can secrete abundant riboflavin (up to 270 nM) to facilitate EET. When an electrode was used as the electron acceptor, the quick recovery of anodizing current after anolyte replacement and the electrochemical behavior of the G. uraniireducens biofilm characterized by differential pulse voltammetry suggest that the self-secreted riboflavin promoted EET by serving as bound redox cofactors for cytochromes. On the contrary, when Fe(III) oxide was the electron acceptor, free riboflavin acted as electron shuttle to mediate the reduction of Fe(III) oxide. The results demonstrate the flexibility of flavins in EET, suggesting that the properties of electron acceptors can affect the binding mode of extracellular flavins, and broaden the knowledge of the EET of Geobacter species.
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Affiliation(s)
- Lingyan Huang
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Jiahuan Tang
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Man Chen
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Xing Liu
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
| | - Shungui Zhou
- Fujian Provincial Key Laboratory of Soil Environmental Health and Regulation, College of Resources and Environment, Fujian Agriculture and Forestry University, Fuzhou, China
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