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Pereira-Garcia C, Sanz-Sáez I, Sánchez P, Coutinho FH, Bravo AG, Sánchez O, Acinas SG. Genomic and transcriptomic characterization of methylmercury detoxification in a deep ocean Alteromonas mediterranea ISS312. Environ Pollut 2024; 347:123725. [PMID: 38467369 DOI: 10.1016/j.envpol.2024.123725] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/03/2023] [Revised: 01/12/2024] [Accepted: 03/04/2024] [Indexed: 03/13/2024]
Abstract
Methylmercury (MeHg) is one of the most worrisome pollutants in marine systems. MeHg detoxification is mediated by merB and merA genes, responsible for the demethylation of MeHg and the reduction of inorganic mercury, respectively. Little is known about the biological capacity to detoxify this compound in marine environments, and even less the bacterial transcriptional changes during MeHg detoxification. This study provides the genomic and transcriptomic characterization of the deep ocean bacteria Alteromonas mediterranea ISS312 with capacity for MeHg degradation. Its genome sequence revealed four mer operons containing three merA gene and two merB gene copies, that could be horizontally transferred among distant related genomes by mobile genetic elements. The transcriptomic profiling in the presence of 5 μM MeHg showed that merA and merB genes are within the most expressed genes, although not all mer genes were equally transcribed. Besides, we aimed to identify functional orthologous genes that displayed expression profiles highly similar or identical to those genes within the mer operons, which could indicate they are under the same regulatory controls. We found contrasting expression profiles for each mer operon that were positively correlated with a wide array of functions mostly related to amino acid metabolism, but also to flagellar assembly or two component systems. Also, this study highlights that all merAB genes of the four operons were globally distributed across oceans layers with higher transcriptional activity in the mesopelagic deeper waters. Our study provides new insights about the transcriptional patterns related to the capacity of marine bacteria to detoxify MeHg, with important implications for the understanding of this process in marine ecosystems.
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Affiliation(s)
- Carla Pereira-Garcia
- Department of Marine Biology and Oceanography, Institut de Ciències del Mar, CSIC, Pg. Marítim de la Barceloneta 37-49, E08003 Barcelona, Catalunya, Spain; Department of Genetics and Microbiology, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Catalunya, Spain.
| | - Isabel Sanz-Sáez
- Department of Marine Biology and Oceanography, Institut de Ciències del Mar, CSIC, Pg. Marítim de la Barceloneta 37-49, E08003 Barcelona, Catalunya, Spain; Department of Environmental Chemistry, IDAEA-CSIC, Barcelona, Catalunya, Spain
| | - Pablo Sánchez
- Department of Marine Biology and Oceanography, Institut de Ciències del Mar, CSIC, Pg. Marítim de la Barceloneta 37-49, E08003 Barcelona, Catalunya, Spain
| | - Felipe H Coutinho
- Department of Marine Biology and Oceanography, Institut de Ciències del Mar, CSIC, Pg. Marítim de la Barceloneta 37-49, E08003 Barcelona, Catalunya, Spain
| | - Andrea G Bravo
- Department of Marine Biology and Oceanography, Institut de Ciències del Mar, CSIC, Pg. Marítim de la Barceloneta 37-49, E08003 Barcelona, Catalunya, Spain
| | - Olga Sánchez
- Department of Genetics and Microbiology, Universitat Autònoma de Barcelona, 08193 Cerdanyola del Vallès, Barcelona, Catalunya, Spain
| | - Silvia G Acinas
- Department of Marine Biology and Oceanography, Institut de Ciències del Mar, CSIC, Pg. Marítim de la Barceloneta 37-49, E08003 Barcelona, Catalunya, Spain.
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Harsonowati W, Rahayuningsih S, Yuniarti E, Susilowati DN, Manohara D, Sipriyadi, Widyaningsih S, Akhdiya A, Suryadi Y, Tentrem T. Bacterial Metal-Scavengers Newly Isolated from Indonesian Gold Mine-Impacted Area: Bacillus altitudinis MIM12 as Novel Tools for Bio-Transformation of Mercury. Microb Ecol 2023; 86:1646-1660. [PMID: 36930295 DOI: 10.1007/s00248-023-02203-z] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/23/2022] [Accepted: 03/02/2023] [Indexed: 06/18/2023]
Abstract
Selikat river, located in the north part of Bengkulu Province, Indonesia, has critical environmental and ecological issues of contamination by mercury due to artisanal small-scale gold mining (ASGM) activities. The present study focused on the identification and bioremediation efficiency of the mercury-resistant bacteria (MRB) isolated from ASGM-impacted areas in Lebong Tambang village, Bengkulu Province, and analyzed their merA gene function in transforming Hg2+ to Hg0. Thirty-four MRB isolates were isolated, and four out of the 34 isolates exhibited not only the highest degree of resistance to Hg (up to 200 ppm) but also to cadmium (Cd), chromium (Cr), copper (Cu), and lead (Pb). Further analysis shows that all four selected isolates harbor a merA operon-encoded mercuric ion (Hg2+) reductase enzyme, with the Hg bioremediation efficiency varying from 71.60 to 91.30%. Additionally, the bioremediation efficiency for Cd, Cr, Cu, and Pb ranged from 54.36 to 98.37%. Among the 34, two isolates identified as Bacillus altitudinis possess effective and superior multi-metal degrading capacity up to 91.30% for Hg, 98.07% for Cu, and 54.36% for Cr. A pilot-scale study exhibited significant in situ bioremediation of Hg from gold mine tailings of 82.10 and 95.16% at 4- and 8-day intervals, respectively. Interestingly, translated nucleotide blast against bacteria and Bacilli merA sequence databases suggested that B. altitudinis harbor merA gene is the first case among Bacilli with the possibility exhibits a novel mechanism of bioremediation, considering our new finding. This study is the first to report the structural and functional Hg-resistant bacterial diversity of unexplored ASGM-impacted areas, emphasizing their biotechnological potential as novel tools for the biological transformation and adsorption of mercury and other toxic metals.
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Affiliation(s)
- Wiwiek Harsonowati
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia.
- Agrobiology and Bioresources Department, School of Agriculture, Utsunomiya University, 350 Mine-Machi, Utsunomiya, 321-8505, Tochigi, Japan.
| | - Sri Rahayuningsih
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
| | - Erny Yuniarti
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
| | - Dwi Ningsih Susilowati
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
| | - Dyah Manohara
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
| | - Sipriyadi
- Biology Department, Faculty of Mathematics and Natural Science, Universitas Bengkulu, Jalan W.R Supratman, Kandang Limun, Bengkulu, 38125, Indonesia
| | - Sri Widyaningsih
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
| | - Alina Akhdiya
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
| | - Yadi Suryadi
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
| | - Titi Tentrem
- Research Center for Horticultural and Estate Crops, Research Organization for Agriculture and Food, National Research and Innovation Agency (BRIN), Cibinong Science Center, Bogor, 16915, Indonesia
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3
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Tada Y, Marumoto K, Iwamoto Y, Takeda K, Sakugawa H. Distribution and phylogeny of mercury methylation, demethylation, and reduction genes in the Seto Inland Sea of Japan. Mar Pollut Bull 2023; 186:114381. [PMID: 36459771 DOI: 10.1016/j.marpolbul.2022.114381] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 06/29/2022] [Revised: 11/08/2022] [Accepted: 11/14/2022] [Indexed: 06/17/2023]
Abstract
Mercury (Hg) adversely affects human and environmental health. To evaluate the mercury (Hg) speciation (methylation, demethylation, and reduction) of microorganisms in coastal seawater, we analyzed the microbial functional gene sets involved in Hg methylation (hgcA and hgcB), demethylation (merB), and reduction (merA) using a metagenomic approach in the eastern and western parts (the Kii and Bungo channels, respectively) of the Seto Inland Sea (SIS) of Japan. We determined the concentration of dissolved total mercury (dTHg) and methylated mercury (dMeHg) in seawater. The metagenomic analysis detected hgcAB, merA, and merB in both channels, whereas the phylogenies of these genes differed between them. A correlation between Hg concentration (both dTHg and dMeHg) and the relative abundance of each gene was not observed. Our data suggests that microbial Hg methylation and demethylation could occur in the SIS and there could be a distinct microbial Hg speciation process between the Kii and Bungo channels.
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Affiliation(s)
- Yuya Tada
- National Institute for Minamata Disease, Department of Environment and Public Health, Kumamoto, Japan.
| | - Kohji Marumoto
- National Institute for Minamata Disease, Department of Environment and Public Health, Kumamoto, Japan
| | - Yoko Iwamoto
- Hiroshima University, Graduate School of Integrated Sciences for Life, Hiroshima, Japan
| | - Kazuhiko Takeda
- Hiroshima University, Graduate School of Integrated Sciences for Life, Hiroshima, Japan
| | - Hiroshi Sakugawa
- Hiroshima University, Graduate School of Integrated Sciences for Life, Hiroshima, Japan
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4
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Al-Ansari MM. Biodetoxification mercury by using a marine bacterium Marinomonas sp. RS3 and its merA gene expression under mercury stress. Environ Res 2022; 205:112452. [PMID: 34856165 DOI: 10.1016/j.envres.2021.112452] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/25/2021] [Revised: 11/21/2021] [Accepted: 11/24/2021] [Indexed: 06/13/2023]
Abstract
Mercury (Hg) pollution in water has been a problem for the ecosystem and human health, thus eco-friendly remediation methods are gaining traction around the world. In this study, a bacterial strain designated as RS3 isolated from the Red Sea (Saudi Arabia) has shown tolerance to more than 250 mg/L of Hg2+ on minimum inhibitory studies. The isolate RS3 was identified as Marinomonas sp., (Accession No: OK271312) using 16s rRNA sequencing. Tracing the growth curve for the RS3 showed that maximum growth attained at 72 h and only 10% reduction than the control medium for 50 mg/L HgCl2 supplemented seawater medium, which continued to reduce as 21% to 60 with the increment of HgCl2 from 100 to 350 mg/L. The Hg2+ removal potential of RS3 is observed to be 78% at 50 mg/L HgCl2/72 h, which is significantly altered with the addition of carbon source such as glucose (84.5%) > fructose (79.8%) > control (78%) > citrate (73.4%) > acetate (60.2%) > maltose (54.7%). Box-Behnken design (BBD) well proposed a model with R2 value of 0.8922, which predict a utmost Hg2+ removal of 89.5% by RS2 at favorable conditions (pH-7; NaC 1% and glucose 5%) at 72 h. Mercuric reductase enzyme encoded merA gene expression was found to be high in RS3 isolates cultivated in 100 mg/L of HgCl2 in comparison with other variables. Thus the seawater isolate Marinomonas sp. RS3 expressed a significant tolerance and removal potential towards the Hg2+, which would make it is a noteworthy applicant for effective mercury remediation practices.
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Affiliation(s)
- Mysoon M Al-Ansari
- Department of Botany and Microbiology, College of Science, King Saud University, Riyadh, 11451, Saudi Arabia.
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5
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Sanz-Sáez I, Pereira-García C, Bravo AG, Trujillo L, Pla i Ferriol M, Capilla M, Sánchez P, Rodríguez Martín-Doimeadios RC, Acinas SG, Sánchez O. Prevalence of Heterotrophic Methylmercury Detoxifying Bacteria across Oceanic Regions. Environ Sci Technol 2022; 56:3452-3461. [PMID: 35245029 PMCID: PMC8928480 DOI: 10.1021/acs.est.1c05635] [Citation(s) in RCA: 5] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 09/27/2021] [Revised: 01/29/2022] [Accepted: 01/31/2022] [Indexed: 05/27/2023]
Abstract
Microbial reduction of inorganic divalent mercury (Hg2+) and methylmercury (MeHg) demethylation is performed by the mer operon, specifically by merA and merB genes, respectively, but little is known about the mercury tolerance capacity of marine microorganisms and its prevalence in the ocean. Here, combining culture-dependent analyses with metagenomic and metatranscriptomic data, we show that marine bacteria that encode mer genes are widespread and active in the global ocean. We explored the distribution of these genes in 290 marine heterotrophic bacteria (Alteromonas and Marinobacter spp.) isolated from different oceanographic regions and depths, and assessed their tolerance to diverse concentrations of Hg2+ and MeHg. In particular, the Alteromonas sp. ISS312 strain presented the highest tolerance capacity and a degradation efficiency for MeHg of 98.2% in 24 h. Fragment recruitment analyses of Alteromonas sp. genomes (ISS312 strain and its associated reconstructed metagenome assembled genome MAG-0289) against microbial bathypelagic metagenomes confirm their prevalence in the deep ocean. Moreover, we retrieved 54 merA and 6 merB genes variants related to the Alteromonas sp. ISS312 strain from global metagenomes and metatranscriptomes from Tara Oceans. Our findings highlight the biological reductive MeHg degradation as a relevant pathway of the ocean Hg biogeochemical cycle.
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Affiliation(s)
- Isabel Sanz-Sáez
- Departament
de Biologia Marina i Oceanografia, Institut
de Ciències del Mar, ICM-CSIC, 08003 Barcelona, Catalunya, Spain
| | - Carla Pereira-García
- Departament
de Biologia Marina i Oceanografia, Institut
de Ciències del Mar, ICM-CSIC, 08003 Barcelona, Catalunya, Spain
| | - Andrea G. Bravo
- Departament
de Biologia Marina i Oceanografia, Institut
de Ciències del Mar, ICM-CSIC, 08003 Barcelona, Catalunya, Spain
| | - Laura Trujillo
- Departament
de Biologia Marina i Oceanografia, Institut
de Ciències del Mar, ICM-CSIC, 08003 Barcelona, Catalunya, Spain
| | - Martí Pla i Ferriol
- Departament
de Genètica i Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
| | - Miguel Capilla
- Research
Group in Environmental Engineering (GI2AM), Department of Chemical
Engineering, University of Valencia, Av. De la Universitat S/N, 46100 Burjassot, Spain
| | - Pablo Sánchez
- Departament
de Biologia Marina i Oceanografia, Institut
de Ciències del Mar, ICM-CSIC, 08003 Barcelona, Catalunya, Spain
| | - Rosa Carmen Rodríguez Martín-Doimeadios
- Environmental
Sciences Institute (ICAM), Department of Analytical Chemistry and
Food Technology, University of Castilla-La
Mancha, Avda. Carlos
III s/n, 45071 Toledo, Spain
| | - Silvia G. Acinas
- Departament
de Biologia Marina i Oceanografia, Institut
de Ciències del Mar, ICM-CSIC, 08003 Barcelona, Catalunya, Spain
| | - Olga Sánchez
- Departament
de Genètica i Microbiologia, Facultat de Biociències, Universitat Autònoma de Barcelona, 08193 Bellaterra, Spain
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Christakis CA, Barkay T, Boyd ES. Expanded Diversity and Phylogeny of mer Genes Broadens Mercury Resistance Paradigms and Reveals an Origin for MerA Among Thermophilic Archaea. Front Microbiol 2021; 12:682605. [PMID: 34248899 PMCID: PMC8261052 DOI: 10.3389/fmicb.2021.682605] [Citation(s) in RCA: 25] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/18/2021] [Accepted: 05/28/2021] [Indexed: 11/13/2022] Open
Abstract
Mercury (Hg) is a highly toxic element due to its high affinity for protein sulfhydryl groups, which upon binding, can destabilize protein structure and decrease enzyme activity. Prokaryotes have evolved enzymatic mechanisms to detoxify inorganic Hg and organic Hg (e.g., MeHg) through the activities of mercuric reductase (MerA) and organomercury lyase (MerB), respectively. Here, the taxonomic distribution and evolution of MerAB was examined in 84,032 archaeal and bacterial genomes, metagenome assembled genomes, and single-cell genomes. Homologs of MerA and MerB were identified in 7.8 and 2.1% percent of genomes, respectively. MerA was identified in the genomes of 10 archaeal and 28 bacterial phyla previously unknown to code for this functionality. Likewise, MerB was identified in 2 archaeal and 11 bacterial phyla previously unknown to encode this functionality. Surprisingly, homologs of MerB were identified in a number of genomes (∼50% of all MerB-encoding genomes) that did not encode MerA, suggesting alternative mechanisms to detoxify Hg(II) once it is generated in the cytoplasm. Phylogenetic reconstruction of MerA place its origin in thermophilic Thermoprotei (Crenarchaeota), consistent with high levels of Hg(II) in geothermal environments, the natural habitat of this archaeal class. MerB appears to have been recruited to the mer operon relatively recently and likely among a mesophilic ancestor of Euryarchaeota and Thaumarchaeota. This is consistent with the functional dependence of MerB on MerA and the widespread distribution of mesophilic microorganisms that methylate Hg(II) at lower temperature. Collectively, these results expand the taxonomic and ecological distribution of mer-encoded functionalities, and suggest that selection for Hg(II) and MeHg detoxification is dependent not only on the availability and type of mercury compounds in the environment but also the physiological potential of the microbes who inhabit these environments. The expanded diversity and environmental distribution of MerAB identify new targets to prioritize for future research.
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Affiliation(s)
- Christos A. Christakis
- Department of Microbiology and Immunology, Montana State University, Bozeman, MT, United States
| | - Tamar Barkay
- Department of Biochemistry and Microbiology, Rutgers, The State University of New Jersey, New Brunswick, NJ, United States
| | - Eric S. Boyd
- Department of Microbiology and Immunology, Montana State University, Bozeman, MT, United States
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Song W, Xiong H, Qi R, Wang S, Yang Y. Effect of salinity and algae biomass on mercury cycling genes and bacterial communities in sediments under mercury contamination: Implications of the mercury cycle in arid regions. Environ Pollut 2021; 269:116141. [PMID: 33290948 DOI: 10.1016/j.envpol.2020.116141] [Citation(s) in RCA: 9] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 07/28/2020] [Revised: 10/22/2020] [Accepted: 11/19/2020] [Indexed: 06/12/2023]
Abstract
Lakes in arid regions are experiencing mercury pollution via air deposition and surface runoff, posing a threat to ecosystem safety and human health. Furthermore, salinity and organic matter input could influence the mercury cycle and composition of bacterial communities in the sediment. In this study, the effects of salinity and algae biomass as an important organic matter on the genes (merA and hgcA) involved in the mercury cycle under mercury contamination were investigated. Archaeal merA and hgcA were not detected in sediments of lake microcosms, indicating that bacteria rather than archaea played a crucial role in mercury reduction and methylation. The high content of mercury (300 ng g-1) could reduce the abundance of both merA and hgcA. The effects of salinity and algae biomass on mercury cycling genes depended on the gene type and dose. A higher input of algae biomass (250 mg L-1) led to an increase of merA abundance, but a decrease of hgcA abundance. All high inputs of mercury, salinity, and algae biomass decreased the richness and diversity of bacterial communities in sediment. Further analysis indicated that higher mercury (300 ng g-1) led to an increased relative abundance of mercury methylators, such as Ruminococcaceae, Bacteroidaceae, and Veillonellaceae. Under saline conditions (10 and 30 g L-1), the richness of specific bacteria associated with mercury reduction (Halomonadaceae) and methylation (Syntrophomonadaceae) increased compared to the control. The input of algae biomass led to an increase in the specific bacterial communities associated with the mercury cycle and the richness of bacteria involved in the decomposition of organic matter. These results provide insight into mercury cycle-related genes and bacterial communities in the sediments of lakes in arid regions.
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Affiliation(s)
- Wenjuan Song
- State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, 830011, China; University of Chinese Academy of Sciences, Beijing, 100049, China.
| | - Heigang Xiong
- College of Applied Arts and Science of Beijing Union University, Beijing, 100191, China
| | - Ran Qi
- Command Center of Comprehensive Natural Resources Survey, China Geological Survey, Beijing, 100055, China; Institute of Geological Survey, China University of Geosciences, Wuhan, 430074, China
| | - Shuzhi Wang
- State Key Laboratory of Desert and Oasis Ecology, Xinjiang Institute of Ecology and Geography, Chinese Academy of Sciences, Urumqi, 830011, China
| | - Yuyi Yang
- Key Laboratory of Aquatic Botany and Watershed Ecology, Wuhan Botanical Garden, Chinese Academy of Sciences, Wuhan, 430074, China
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Arregui G, Hipólito P, Pallol B, Lara-Dampier V, García-Rodríguez D, Varela HP, Tavakoli Zaniani P, Balomenos D, Paape T, Coba de la Peña T, Lucas MM, Pueyo JJ. Mercury-Tolerant Ensifer medicae Strains Display High Mercuric Reductase Activity and a Protective Effect on Nitrogen Fixation in Medicago truncatula Nodules Under Mercury Stress. Front Plant Sci 2021; 11:560768. [PMID: 33519831 PMCID: PMC7840509 DOI: 10.3389/fpls.2020.560768] [Citation(s) in RCA: 3] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/10/2020] [Accepted: 12/22/2020] [Indexed: 05/27/2023]
Abstract
Mercury (Hg) is extremely toxic for all living organisms. Hg-tolerant symbiotic rhizobia have the potential to increase legume tolerance, and to our knowledge, the mechanisms underlying Hg tolerance in rhizobia have not been investigated to date. Rhizobial strains of Ensifer medicae, Rhizobium leguminosarum bv. trifolii and Bradyrhizobium canariense previously isolated from severely Hg-contaminated soils showed different levels of Hg tolerance. The ability of the strains to reduce mercury Hg2+ to Hg0, a volatile and less toxic form of mercury, was assessed using a Hg volatilization assay. In general, tolerant strains displayed high mercuric reductase activity, which appeared to be inducible in some strains when grown at a sub-lethal HgCl2 concentration. A strong correlation between Hg tolerance and mercuric reductase activity was observed for E. medicae strains, whereas this was not the case for the B. canariense strains, suggesting that additional Hg tolerance mechanisms could be playing a role in B. canariense. Transcript abundance from merA, the gene that encodes mercuric reductase, was quantified in tolerant and sensitive E. medicae and R. leguminosarum strains. Tolerant strains presented higher merA expression than sensitive ones, and an increase in transcript abundance was observed for some strains when bacteria were grown in the presence of a sub-lethal HgCl2 concentration. These results suggest a regulation of mercuric reductase in rhizobia. Expression of merA genes and mercuric reductase activity were confirmed in Medicago truncatula nodules formed by a sensitive or a tolerant E. medicae strain. Transcript accumulation in nodules formed by the tolerant strain increased when Hg stress was applied, while a significant decrease in expression occurred upon stress application in nodules formed by the Hg-sensitive strain. The effect of Hg stress on nitrogen fixation was evaluated, and in our experimental conditions, nitrogenase activity was not affected in nodules formed by the tolerant strain, while a significant decrease in activity was observed in nodules elicited by the Hg-sensitive bacteria. Our results suggest that the combination of tolerant legumes with tolerant rhizobia constitutes a potentially powerful tool in the bioremediation of Hg-contaminated soils.
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Affiliation(s)
- Gabriela Arregui
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | - Pablo Hipólito
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | - Beatriz Pallol
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | - Victoria Lara-Dampier
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | - Diego García-Rodríguez
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | - Higinio P. Varela
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | | | | | - Timothy Paape
- Brookhaven National Laboratory, Upton, NY, United States
| | | | - M. Mercedes Lucas
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
| | - José J. Pueyo
- Department of Soil, Plant and Environmental Quality, Institute of Agricultural Sciences, ICA-CSIC, Madrid, Spain
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9
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Gionfriddo CM, Stott MB, Power JF, Ogorek JM, Krabbenhoft DP, Wick R, Holt K, Chen LX, Thomas BC, Banfield JF, Moreau JW. Genome-Resolved Metagenomics and Detailed Geochemical Speciation Analyses Yield New Insights into Microbial Mercury Cycling in Geothermal Springs. Appl Environ Microbiol 2020; 86:e00176-20. [PMID: 32414793 DOI: 10.1128/AEM.00176-20] [Citation(s) in RCA: 10] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/03/2020] [Accepted: 05/07/2020] [Indexed: 12/18/2022] Open
Abstract
Geothermal systems emit substantial amounts of aqueous, gaseous, and methylated mercury, but little is known about microbial influences on mercury speciation. Here, we report results from genome-resolved metagenomics and mercury speciation analysis of acidic warm springs in the Ngawha Geothermal Field (<55°C, pH <4.5), Northland Region, Aotearoa New Zealand. Our aim was to identify the microorganisms genetically equipped for mercury methylation, demethylation, or Hg(II) reduction to volatile Hg(0) in these springs. Dissolved total and methylated mercury concentrations in two adjacent springs with different mercury speciation ranked among the highest reported from natural sources (250 to 16,000 ng liter-1 and 0.5 to 13.9 ng liter-1, respectively). Total solid mercury concentrations in spring sediments ranged from 1,274 to 7,000 μg g-1 In the context of such ultrahigh mercury levels, the geothermal microbiome was unexpectedly diverse and dominated by acidophilic and mesophilic sulfur- and iron-cycling bacteria, mercury- and arsenic-resistant bacteria, and thermophilic and acidophilic archaea. By integrating microbiome structure and metagenomic potential with geochemical constraints, we constructed a conceptual model for biogeochemical mercury cycling in geothermal springs. The model includes abiotic and biotic controls on mercury speciation and illustrates how geothermal mercury cycling may couple to microbial community dynamics and sulfur and iron biogeochemistry.IMPORTANCE Little is currently known about biogeochemical mercury cycling in geothermal systems. The manuscript presents a new conceptual model, supported by genome-resolved metagenomic analysis and detailed geochemical measurements. The model illustrates environmental factors that influence mercury cycling in acidic springs, including transitions between solid (mineral) and aqueous phases of mercury, as well as the interconnections among mercury, sulfur, and iron cycles. This work provides a framework for studying natural geothermal mercury emissions globally. Specifically, our findings have implications for mercury speciation in wastewaters from geothermal power plants and the potential environmental impacts of microbially and abiotically formed mercury species, particularly where they are mobilized in spring waters that mix with surface or groundwaters. Furthermore, in the context of thermophilic origins for microbial mercury volatilization, this report yields new insights into how such processes may have evolved alongside microbial mercury methylation/demethylation and the environmental constraints imposed by the geochemistry and mineralogy of geothermal systems.
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Osterwalder S, Huang JH, Shetaya WH, Agnan Y, Frossard A, Frey B, Alewell C, Kretzschmar R, Biester H, Obrist D. Mercury emission from industrially contaminated soils in relation to chemical, microbial, and meteorological factors. Environ Pollut 2019; 250:944-952. [PMID: 31085481 DOI: 10.1016/j.envpol.2019.03.093] [Citation(s) in RCA: 14] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 12/04/2018] [Revised: 03/21/2019] [Accepted: 03/22/2019] [Indexed: 06/09/2023]
Abstract
The Minamata Convention entered into force in 2017 with the aim to phase-out the use of mercury (Hg) in manufacturing processes such as the chlor-alkali or vinyl chloride monomer production. However, past industrial use of Hg had already resulted in extensive soil pollution, which poses a potential environmental threat. We investigated the emission of gaseous elemental mercury (Hg0) from Hg polluted soils in settlement areas in the canton of Valais, Switzerland, and its impact on local air Hg concentrations. Most soil Hg was found as soil matrix-bound divalent Hg (HgII). Elemental mercury (Hg0) was undetectable in soils, yet we observed substantial Hg0 emission (20-1392 ng m-2 h-1) from 27 soil plots contaminated with Hg (0.2-390 mg Hg kg-1). The emissions of Hg0 were calculated for 1274 parcels covering an area of 8.6 km2 of which 12% exceeded the Swiss soil remediation threshold of 2 mg Hg kg-1. The annual Hg0 emission from this area was approximately 6 kg a-1, which is almost 1% of the total atmospheric Hg emissions in Switzerland based on emission inventory estimates. Our results show a higher abundance of Hg resistance genes (merA) in soil microbial communities with increasing soil Hg concentrations, indicating that biotic reduction of HgII is likely an important pathway to form volatile Hg0 in these soils. The total soil Hg pool in the top 20 cm of the investigated area was 4288 kg; hence, if not remediated, these contaminated soils remain a long-term source of atmospheric Hg, which is prone to long-range atmospheric transport.
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Affiliation(s)
- Stefan Osterwalder
- Environmental Geosciences, University of Basel, 4056 Basel, Switzerland; Department of Forest Ecology and Management, Swedish University of Agricultural Sciences, 901 83 Umeå, Sweden.
| | - Jen-How Huang
- Environmental Geosciences, University of Basel, 4056 Basel, Switzerland
| | - Waleed H Shetaya
- Environmental Geosciences, University of Basel, 4056 Basel, Switzerland; Air Pollution Research Department, Environmental Research Division, National Research Centre, Dokki, Giza 12622, Egypt
| | - Yannick Agnan
- Sorbonne Université, CNRS, EPHE, UMR Metis, 75252 Paris, France
| | - Aline Frossard
- Federal Research Institute WSL, 8903 Birmensdorf, Switzerland
| | - Beat Frey
- Federal Research Institute WSL, 8903 Birmensdorf, Switzerland
| | - Christine Alewell
- Environmental Geosciences, University of Basel, 4056 Basel, Switzerland
| | - Ruben Kretzschmar
- Institute of Biogeochemistry and Pollutant Dynamics, CHN, ETH Zürich, Zürich, Switzerland
| | - Harald Biester
- Institut für Geökologie, AG Umweltgeochemie, Technische Universität Braunschweig, 38106 Braunschweig, Germany
| | - Daniel Obrist
- Department of Environmental, Earth and Atmospheric Sciences, University of Massachusetts, Lowell, MA 01854, USA
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Yang J, Takaoka M, Sano A, Matsuyama A, Yanase R. Vertical Distribution of Total Mercury and Mercury Methylation in a Landfill Site in Japan. Int J Environ Res Public Health 2018; 15:ijerph15061252. [PMID: 29899229 PMCID: PMC6025181 DOI: 10.3390/ijerph15061252] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 05/15/2018] [Revised: 06/05/2018] [Accepted: 06/08/2018] [Indexed: 11/25/2022]
Abstract
Mercury is a neurotoxin, with certain organic forms of the element being particularly harmful to humans. The Minamata Convention was adopted to reduce the intentional use and emission of mercury. Because mercury is an element, it cannot be decomposed. Mercury-containing products and mercury used for various processes will eventually enter the waste stream, and landfill sites will become a mercury sink. While landfill sites can be a source of mercury pollution, the behavior of mercury in solid waste within a landfill site is still not fully understood. The purpose of this study was to determine the depth profile of mercury, the levels of methyl mercury (MeHg), and the factors controlling methylation in an old landfill site that received waste for over 30 years. Three sampling cores were selected, and boring sampling was conducted to a maximum depth of 18 m, which reached the bottom layer of the landfill. Total mercury (THg) and MeHg were measured in the samples to determine the characteristics of mercury at different depths. Bacterial species were identified by 16S rRNA amplification and sequencing, because the methylation process is promoted by a series of genes. It was found that the THg concentration was 19–975 ng/g, with a geometric mean of 298 ng/g, which was slightly less than the 400 ng/g concentration recorded 30 years previously. In some samples, MeHg accounted for up to 15–20% of THg, which is far greater than the general level in soils and sediments, although the source of MeHg was unclear. The genetic data indicated that hgcA was present mostly in the upper and lower layers of the three cores, merA was almost as much as hgcA, while the level of merB was hundreds of times less than those of the other two genes. A significant correlation was found between THg and MeHg, as well as between MeHg and MeHg/THg. In addition, a negative correlation was found between THg and merA. The coexistence of the three genes indicated that both methylation and demethylation processes could occur, but the lack of merB was a barrier for demethylation.
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Affiliation(s)
- Jing Yang
- Department of Environmental Engineering, Graduate School of Engineering, Kyoto University, C-kluster, Kyotodaigakukatsura, Nishikyo-ku, Kyoto 6158540, Japan.
| | - Masaki Takaoka
- Department of Environmental Engineering, Graduate School of Engineering, Kyoto University, C-kluster, Kyotodaigakukatsura, Nishikyo-ku, Kyoto 6158540, Japan.
- Graduate School of Global Environmental Studies, Kyoto University, C-kluster, Kyotodaigakukatsura, Nishikyo-ku, Kyoto 6158540, Japan.
| | - Akira Sano
- Graduate School of Global Environmental Studies, Kyoto University, C-kluster, Kyotodaigakukatsura, Nishikyo-ku, Kyoto 6158540, Japan.
| | - Akito Matsuyama
- National Institute for Minamata Disease, 4058-18 Hama, Minamata-City, Kumamoto 8670008, Japan.
| | - Ryuji Yanase
- Environmental Protection Center, Fukuoka University, 8-19-1 Nanakuma, Jonan-ku, Fukuoka 8140180, Japan.
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Porwal S, Singh R. Cloning of merA Gene from Methylotenera Mobilis for Mercury Biotransformation. Indian J Microbiol 2016; 56:504-507. [PMID: 27784949 DOI: 10.1007/s12088-016-0613-5] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/23/2015] [Accepted: 07/22/2016] [Indexed: 10/21/2022] Open
Abstract
Mercury (Hg) is one of the most toxic heavy metal and is extremely harmful for the environment. The permissible limit of mercury in industrial effluents is 0.001 ppm, whereas there are various sites having very high levels of mercury contamination. In the present study, 10 different mercury (Hg) resistant bacterial strains were isolated from Ulhas Estuary, Mumbai (Hg concentration of 107 ppm). All the strains were subsequently grown on higher concentration of mercuric chloride (HgCl2), one of the isolate (USP5) showed significant growth at high concentration of Hg (40 ppm) and 16S rRNA gene sequencing revealed the identity of the bacterium as Methylotenera mobilis, (Accession no. KT714144). The mer operon was isolated and cloned in E.coli and checked for its ability to tolerate higher concentration of Hg. It has shown growth up to 70 ppm of Hg, also presence of merA gene indicated its ability to detoxify Hg into less toxic volatile form. The atomic absorption spectrophotometry confirmed the ability of clone to efficiently detoxify 60-90 % of the Hg (10-70 ppm) within 48-72 h. This clone can be used for effective volatilization of Hg from contaminated areas.
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Affiliation(s)
- Shalini Porwal
- Amity Institute of Microbial Biotechnology, Amity University, Sector-125, Noida, Uttar Pradesh 201303 India
| | - Rajni Singh
- Amity Institute of Microbial Biotechnology, Amity University, Sector-125, Noida, Uttar Pradesh 201303 India
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Kovac Virsek M, Hubad B, Lapanje A. Mercury induced community tolerance in microbial biofilms is related to pollution gradients in a long-term polluted river. Aquat Toxicol 2013; 144-145:208-17. [PMID: 24184840 DOI: 10.1016/j.aquatox.2013.09.023] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/07/2013] [Revised: 09/19/2013] [Accepted: 09/20/2013] [Indexed: 05/27/2023]
Abstract
The net toxicity of different forms of mercury, in the long-term during their transformation processes, leads to the selection of resistant bacterial cells and this result in community tolerance which is pollution induced. Accordingly, based on profiles of a bacterial community structure, analysis of Hg resistant culturable bacteria and quantification of merA genes, we assessed development of pollution induced community tolerance in a mercury-polluted gradient in the Idrijca River. TTGE analysis did not show effects of mercury pollution to bacterial community diversity, while quantification of merA genes showed that merA genes can be correlated precisely (R(2)=0.83) with the total concentration of mercury in the biofilm microbial communities in the pollution gradient.
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Affiliation(s)
- Manca Kovac Virsek
- Institute of Microbial Sciences and Technologies Ltd., Askerceva 59, 1230 Domzale, Slovenia
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Holmsgaard PN, Sørensen SJ, Hansen LH. Simultaneous pyrosequencing of the 16S rRNA, IncP-1 trfA, and merA genes. J Microbiol Methods 2013; 95:280-4. [PMID: 24080123 DOI: 10.1016/j.mimet.2013.09.016] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/11/2013] [Revised: 09/20/2013] [Accepted: 09/20/2013] [Indexed: 11/24/2022]
Abstract
The use of amplicon pyrosequencing makes it possible to produce thousands of sequences of the same gene at relatively low costs. Here we show that it is possible to simultaneously sequence the 16S rRNA gene, IncP-1 trfA gene and mercury reductase gene (merA) as a way for screening the diversity of several genes in the same samples. As a proof-of-concept two different soil samples and a wastewater sample were screened. Multiplexing identifiers (MIDs) and sequencing adapters were added to amplicons using a tailed PCR approach and the universal overhangs U1 and U2 for this approach were redesigned. Furthermore, this is the first time the IncP-1 plasmid diversity was studied by amplicon pyrosequencing and for this purpose a clustering threshold of 89% nucleotide sequence similarity was determined to differentiate the IncP-1 subgroups.
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Boyd ES, Barkay T. The mercury resistance operon: from an origin in a geothermal environment to an efficient detoxification machine. Front Microbiol 2012; 3:349. [PMID: 23087676 PMCID: PMC3466566 DOI: 10.3389/fmicb.2012.00349] [Citation(s) in RCA: 150] [Impact Index Per Article: 12.5] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/27/2012] [Accepted: 09/11/2012] [Indexed: 11/21/2022] Open
Abstract
Mercuric mercury (Hg[II]) is a highly toxic and mobile element that is likely to have had a pronounced and adverse effect on biology since Earth’s oxygenation ∼2.4 billion years ago due to its high affinity for protein sulfhydryl groups, which upon binding destabilize protein structure and decrease enzyme activity, resulting in a decreased organismal fitness. The central enzyme in the microbial mercury detoxification system is the mercuric reductase (MerA) protein, which catalyzes the reduction of Hg(II) to volatile Hg(0). In addition to MerA, mer operons encode for proteins involved in regulation, Hg binding, and organomercury degradation. Mer-mediated approaches have had broad applications in the bioremediation of mercury-contaminated environments and industrial waste streams. Here, we examine the composition of 272 individual mer operons and quantitatively map the distribution of mer-encoded functions on both taxonomic SSU rRNA gene and MerA phylogenies. The results indicate an origin and early evolution of MerA among thermophilic bacteria and an overall increase in the complexity of mer operons through evolutionary time, suggesting continual gene recruitment and evolution leading to an improved efficiency and functional potential of the Mer detoxification system. Consistent with a positive relationship between the evolutionary history and topology of MerA and SSU rRNA gene phylogenies (Mantel R = 0.81, p < 0.01), the distribution of the majority of mer functions, when mapped on these phylograms, indicates an overall tendency to inherit mer-encoded functions through vertical descent. However, individual mer functions display evidence of a variable degree of vertical inheritance, with several genes exhibiting strong evidence for acquisition via lateral gene transfer and/or gene loss. Collectively, these data suggest that (i) mer has evolved from a simple system in geothermal environments to a widely distributed and more complex and efficient detoxification system, and (ii) merA is a suitable biomarker for examining the functional diversity of Hg detoxification and for predicting the composition of mer operons in natural environments.
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Affiliation(s)
- Eric S Boyd
- Department of Chemistry and Biochemistry, Montana State University Bozeman, MT, USA
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