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Hiralal A, Geelhoed JS, Neukirchen S, Meysman FJR. Comparative genomic analysis of nickel homeostasis in cable bacteria. BMC Genomics 2024; 25:692. [PMID: 39009997 PMCID: PMC11247825 DOI: 10.1186/s12864-024-10594-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2024] [Accepted: 07/03/2024] [Indexed: 07/17/2024] Open
Abstract
BACKGROUND Cable bacteria are filamentous members of the Desulfobulbaceae family that are capable of performing centimetre‑scale electron transport in marine and freshwater sediments. This long‑distance electron transport is mediated by a network of parallel conductive fibres embedded in the cell envelope. This fibre network efficiently transports electrical currents along the entire length of the centimetre‑long filament. Recent analyses show that these fibres consist of metalloproteins that harbour a novel nickel‑containing cofactor, which indicates that cable bacteria have evolved a unique form of biological electron transport. This nickel‑dependent conduction mechanism suggests that cable bacteria are strongly dependent on nickel as a biosynthetic resource. Here, we performed a comprehensive comparative genomic analysis of the genes linked to nickel homeostasis. We compared the genome‑encoded adaptation to nickel of cable bacteria to related members of the Desulfobulbaceae family and other members of the Desulfobulbales order. RESULTS Presently, four closed genomes are available for the monophyletic cable bacteria clade that consists of the genera Candidatus Electrothrix and Candidatus Electronema. To increase the phylogenomic coverage, we additionally generated two closed genomes of cable bacteria: Candidatus Electrothrix gigas strain HY10‑6 and Candidatus Electrothrix antwerpensis strain GW3‑4, which are the first closed genomes of their respective species. Nickel homeostasis genes were identified in a database of 38 cable bacteria genomes (including 6 closed genomes). Gene prevalence was compared to 19 genomes of related strains, residing within the Desulfobulbales order but outside of the cable bacteria clade, revealing several genome‑encoded adaptations to nickel homeostasis in cable bacteria. Phylogenetic analysis indicates that nickel importers, nickel‑binding enzymes and nickel chaperones of cable bacteria are affiliated to organisms outside the Desulfobulbaceae family, with several proteins showing affiliation to organisms outside of the Desulfobacterota phylum. Conspicuously, cable bacteria encode a unique periplasmic nickel export protein RcnA, which possesses a putative cytoplasmic histidine‑rich loop that has been largely expanded compared to RcnA homologs in other organisms. CONCLUSION Cable bacteria genomes show a clear genetic adaptation for nickel utilization when compared to closely related genera. This fully aligns with the nickel‑dependent conduction mechanism that is uniquely found in cable bacteria.
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Affiliation(s)
- Anwar Hiralal
- Geobiology Research Group, University of Antwerp, Antwerp, Belgium
| | | | - Sinje Neukirchen
- Geobiology Research Group, University of Antwerp, Antwerp, Belgium
| | - Filip J R Meysman
- Geobiology Research Group, University of Antwerp, Antwerp, Belgium.
- Department of Biotechnology, Delft University of Technology, Delft, The Netherlands.
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Xiong X, Li Y, Zhang C. Cable bacteria: Living electrical conduits for biogeochemical cycling and water environment restoration. WATER RESEARCH 2024; 253:121345. [PMID: 38394932 DOI: 10.1016/j.watres.2024.121345] [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: 11/29/2023] [Revised: 02/17/2024] [Accepted: 02/19/2024] [Indexed: 02/25/2024]
Abstract
Since the discovery of multicellular cable bacteria in marine sediments in 2012, they have attracted widespread attention and interest due to their unprecedented ability to generate and transport electrical currents over centimeter-scale long-range distances. The cosmopolitan distribution of cable bacteria in both marine and freshwater systems, along with their substantial impact on local biogeochemistry, has uncovered their important role in element cycling and ecosystem functioning of aquatic environments. Considerable research efforts have been devoted to the potential utilization of cable bacteria for various water management purposes during the past few years. However, there lacks a critical summary on the advances and contributions of cable bacteria to biogeochemical cycles and water environment restoration. This review aims to provide an up-to-date and comprehensive overview of the current research on cable bacteria, with a particular view on their participation in aquatic biogeochemical cycles and promising applications in water environment restoration. It systematically analyzes (i) the global distribution of cable bacteria in aquatic ecosystems and the major environmental factors affecting their survival, diversity, and composition, (ii) the interactive associations between cable bacteria and other microorganisms as well as aquatic plants and infauna, (iii) the underlying role of cable bacteria in sedimentary biogeochemical cycling of essential elements including but not limited to sulfur, iron, phosphorus, and nitrogen, (iv) the practical explorations of cable bacteria for water pollution control, greenhouse gas emission reduction, aquatic ecological environment restoration, as well as possible combinations with other water remediation technologies. It is believed to give a step-by-step introduction to progress on cable bacteria, highlight key findings, opportunities and challenges of using cable bacteria for water environment restoration, and propose directions for further exploration.
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Affiliation(s)
- Xinyan Xiong
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210024, PR China
| | - Yi Li
- Key Laboratory of Integrated Regulation and Resource Development on Shallow Lake of Ministry of Education, College of Environment, Hohai University, Nanjing 210024, PR China.
| | - Chi Zhang
- College of Materials Science and Engineering, Hohai University, Changzhou 213200, PR China.
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Smets B, Boschker HTS, Wetherington MT, Lelong G, Hidalgo-Martinez S, Polerecky L, Nuyts G, De Wael K, Meysman FJR. Multi-wavelength Raman microscopy of nickel-based electron transport in cable bacteria. Front Microbiol 2024; 15:1208033. [PMID: 38525072 PMCID: PMC10959288 DOI: 10.3389/fmicb.2024.1208033] [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] [Received: 04/18/2023] [Accepted: 02/26/2024] [Indexed: 03/26/2024] Open
Abstract
Cable bacteria embed a network of conductive protein fibers in their cell envelope that efficiently guides electron transport over distances spanning up to several centimeters. This form of long-distance electron transport is unique in biology and is mediated by a metalloprotein with a sulfur-coordinated nickel (Ni) cofactor. However, the molecular structure of this cofactor remains presently unknown. Here, we applied multi-wavelength Raman microscopy to identify cell compounds linked to the unique cable bacterium physiology, combined with stable isotope labeling, and orientation-dependent and ultralow-frequency Raman microscopy to gain insight into the structure and organization of this novel Ni-cofactor. Raman spectra of native cable bacterium filaments reveal vibrational modes originating from cytochromes, polyphosphate granules, proteins, as well as the Ni-cofactor. After selective extraction of the conductive fiber network from the cell envelope, the Raman spectrum becomes simpler, and primarily retains vibrational modes associated with the Ni-cofactor. These Ni-cofactor modes exhibit intense Raman scattering as well as a strong orientation-dependent response. The signal intensity is particularly elevated when the polarization of incident laser light is parallel to the direction of the conductive fibers. This orientation dependence allows to selectively identify the modes that are associated with the Ni-cofactor. We identified 13 such modes, some of which display strong Raman signals across the entire range of applied wavelengths (405-1,064 nm). Assignment of vibrational modes, supported by stable isotope labeling, suggest that the structure of the Ni-cofactor shares a resemblance with that of nickel bis(1,2-dithiolene) complexes. Overall, our results indicate that cable bacteria have evolved a unique cofactor structure that does not resemble any of the known Ni-cofactors in biology.
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Affiliation(s)
- Bent Smets
- Department of Biology, University of Antwerp, Antwerp, Belgium
| | - Henricus T. S. Boschker
- Department of Biology, University of Antwerp, Antwerp, Belgium
- Department of Biotechnology, Delft University of Technology, Delft, Netherlands
| | - Maxwell T. Wetherington
- Materials Characterization Laboratory, Pennsylvania State University, State College, PA, United States
| | - Gérald Lelong
- Institut de Minéralogie, de Physique des Matériaux et Cosmochimie (IMPMC), Sorbonne Universités, France—Muséum National d’Histoire Naturelle, Paris, France
| | | | - Lubos Polerecky
- Department of Earth Sciences, Utrecht University, Utrecht, Netherlands
| | - Gert Nuyts
- Department of Bioscience Engineering, University of Antwerp, Antwerp, Belgium
- Department of Physics, University of Antwerp, Antwerp, Belgium
| | - Karolien De Wael
- Department of Bioscience Engineering, University of Antwerp, Antwerp, Belgium
| | - Filip J. R. Meysman
- Department of Biology, University of Antwerp, Antwerp, Belgium
- Department of Biotechnology, Delft University of Technology, Delft, Netherlands
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Hiralal A, Geelhoed JS, Hidalgo-Martinez S, Smets B, van Dijk JR, Meysman FJR. Closing the genome of unculturable cable bacteria using a combined metagenomic assembly of long and short sequencing reads. Microb Genom 2024; 10:001197. [PMID: 38376381 PMCID: PMC10926707 DOI: 10.1099/mgen.0.001197] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/13/2023] [Accepted: 01/23/2024] [Indexed: 02/21/2024] Open
Abstract
Many environmentally relevant micro-organisms cannot be cultured, and even with the latest metagenomic approaches, achieving complete genomes for specific target organisms of interest remains a challenge. Cable bacteria provide a prominent example of a microbial ecosystem engineer that is currently unculturable. They occur in low abundance in natural sediments, but due to their capability for long-distance electron transport, they exert a disproportionately large impact on the biogeochemistry of their environment. Current available genomes of marine cable bacteria are highly fragmented and incomplete, hampering the elucidation of their unique electrogenic physiology. Here, we present a metagenomic pipeline that combines Nanopore long-read and Illumina short-read shotgun sequencing. Starting from a clonal enrichment of a cable bacterium, we recovered a circular metagenome-assembled genome (5.09 Mbp in size), which represents a novel cable bacterium species with the proposed name Candidatus Electrothrix scaldis. The closed genome contains 1109 novel identified genes, including key metabolic enzymes not previously described in incomplete genomes of cable bacteria. We examined in detail the factors leading to genome closure. Foremost, native, non-amplified long reads are crucial to resolve the many repetitive regions within the genome of cable bacteria, and by analysing the whole metagenomic assembly, we found that low strain diversity is key for achieving genome closure. The insights and approaches presented here could help achieve genome closure for other keystone micro-organisms present in complex environmental samples at low abundance.
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Affiliation(s)
- Anwar Hiralal
- Geobiology Research Group, University of Antwerp, Antwerp, Belgium
| | | | | | - Bent Smets
- Geobiology Research Group, University of Antwerp, Antwerp, Belgium
| | | | - Filip J. R. Meysman
- Geobiology Research Group, University of Antwerp, Antwerp, Belgium
- Department of Biotechnology, Delft University of Technology, Delft, Netherlands
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Plum-Jensen LE, Schramm A, Marshall IPG. First single-strain enrichments of Electrothrix cable bacteria, description of E. aestuarii sp. nov. and E. rattekaaiensis sp. nov., and proposal of a cable bacteria taxonomy following the rules of the SeqCode. Syst Appl Microbiol 2024; 47:126487. [PMID: 38295603 DOI: 10.1016/j.syapm.2024.126487] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/30/2023] [Revised: 12/23/2023] [Accepted: 01/15/2024] [Indexed: 02/02/2024]
Abstract
Cable bacteria are electrically conductive, filamentous Desulfobulbaceae, which are morphologically, functionally, and phylogenetically distinct from the other members of this family. Cable bacteria have not been obtained in pure culture and were therefore previously described as candidate genera, Candidatus Electrothrix and Ca. Electronema; a representative of the latter is available as single-strain sediment enrichment. Here we present an improved workflow to obtain the first single-strain enrichments of Ca. Electrothrix and report their metagenome-assembled genomes (MAGs) and morphology. Based on these results and on previously published high-quality MAGs and morphological data of cable bacteria from both candidate genera, we propose to adopt the genus names Electrothrix and Electronema following the rules of the Code of Nomenclature of Prokaryotes Described from Sequence Data (SeqCode), with Electrothrix communis RBTS and Electronema aureum GSTS, respectively, as the nomenclatural types of the genera. Furthermore, based on average nucleotide identity (ANI) values < 95 % with any described species, we propose two of our three single-strain enrichment cultures as novel species of the genus Electrothrix, with the names E. aestuarii sp. nov. and E. rattekaaiensis sp. nov., according to the SeqCode.
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Affiliation(s)
- Lea E Plum-Jensen
- Center for Electromicrobiology, Section for Microbiology, Department of Biology, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark.
| | - Andreas Schramm
- Center for Electromicrobiology, Section for Microbiology, Department of Biology, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark.
| | - Ian P G Marshall
- Center for Electromicrobiology, Section for Microbiology, Department of Biology, Aarhus University, Ny Munkegade 114, DK-8000 Aarhus C, Denmark.
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