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Kammel M, Erdmann C, Sawers RG. The formate-hydrogen axis and its impact on the physiology of enterobacterial fermentation. Adv Microb Physiol 2024; 84:51-82. [PMID: 38821634 DOI: 10.1016/bs.ampbs.2024.02.002] [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] [Indexed: 06/02/2024]
Abstract
Formic acid (HCOOH) and dihydrogen (H2) are characteristic products of enterobacterial mixed-acid fermentation, with H2 generation increasing in conjunction with a decrease in extracellular pH. Formate and acetyl-CoA are generated by radical-based and coenzyme A-dependent cleavage of pyruvate catalysed by pyruvate formate-lyase (PflB). Formate is also the source of H2, which is generated along with carbon dioxide through the action of the membrane-associated, cytoplasmically-oriented formate hydrogenlyase (FHL-1) complex. Synthesis of the FHL-1 complex is completely dependent on the cytoplasmic accumulation of formate. Consequently, formate determines its own disproportionation into H2 and CO2 by the FHL-1 complex. Cytoplasmic formate levels are controlled by FocA, a pentameric channel that translocates formic acid/formate bidirectionally between the cytoplasm and periplasm. Each protomer of FocA has a narrow hydrophobic pore through which neutral formic acid can pass. Two conserved amino acid residues, a histidine and a threonine, at the center of the pore control directionality of translocation. The histidine residue is essential for pH-dependent influx of formic acid. Studies with the formate analogue hypophosphite and amino acid variants of FocA suggest that the mechanisms of formic acid efflux and influx differ. Indeed, current data suggest, depending on extracellular formate levels, two separate uptake mechanisms exist, both likely contributing to maintain pH homeostasis. Bidirectional formate/formic acid translocation is dependent on PflB and influx requires an active FHL-1 complex. This review describes the coupling of formate and H2 production in enterobacteria.
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Affiliation(s)
- Michelle Kammel
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany
| | - Christopher Erdmann
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany
| | - R Gary Sawers
- Institute of Microbiology, Martin Luther University Halle-Wittenberg, Halle, Saale, Germany.
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Metcalfe GD, Sargent F, Hippler M. Hydrogen production in the presence of oxygen by Escherichia coli K-12. MICROBIOLOGY (READING, ENGLAND) 2022; 168. [PMID: 35343886 PMCID: PMC9558352 DOI: 10.1099/mic.0.001167] [Citation(s) in RCA: 9] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Indexed: 12/31/2022]
Abstract
Escherichia coli is a facultative anaerobe that can grow in a variety of environmental conditions. In the complete absence of O2, E. coli can perform a mixed-acid fermentation that contains within it an elaborate metabolism of formic acid. In this study, we use cavity-enhanced Raman spectroscopy (CERS), FTIR, liquid Raman spectroscopy, isotopic labelling and molecular genetics to make advances in the understanding of bacterial formate and H2 metabolism. It is shown that, under anaerobic (anoxic) conditions, formic acid is generated endogenously, excreted briefly from the cell, and then taken up again to be disproportionated to H2 and CO2 by formate hydrogenlyase (FHL-1). However, exogenously added D-labelled formate behaves quite differently from the endogenous formate and is taken up immediately, independently, and possibly by a different mechanism, by the cell and converted to H2 and CO2. Our data support an anion-proton symport model for formic acid transport. In addition, when E. coli was grown in a micro-aerobic (micro-oxic) environment it was possible to analyse aspects of formate and O2 respiration occurring alongside anaerobic metabolism. While cells growing under micro-aerobic conditions generated endogenous formic acid, no H2 was produced. However, addition of exogenous formate at the outset of cell growth did induce FHL-1 biosynthesis and resulted in formate-dependent H2 production in the presence of O2.
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Affiliation(s)
- George D Metcalfe
- Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
| | - Frank Sargent
- School of Natural & Environmental Sciences, Newcastle University, Newcastle upon Tyne NE1 7RU, UK
| | - Michael Hippler
- Department of Chemistry, University of Sheffield, Sheffield S3 7HF, UK
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Gazitúa MC, Vik DR, Roux S, Gregory AC, Bolduc B, Widner B, Mulholland MR, Hallam SJ, Ulloa O, Sullivan MB. Potential virus-mediated nitrogen cycling in oxygen-depleted oceanic waters. THE ISME JOURNAL 2021; 15:981-998. [PMID: 33199808 PMCID: PMC8115048 DOI: 10.1038/s41396-020-00825-6] [Citation(s) in RCA: 56] [Impact Index Per Article: 18.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 04/23/2020] [Revised: 09/30/2020] [Accepted: 10/27/2020] [Indexed: 01/29/2023]
Abstract
Viruses play an important role in the ecology and biogeochemistry of marine ecosystems. Beyond mortality and gene transfer, viruses can reprogram microbial metabolism during infection by expressing auxiliary metabolic genes (AMGs) involved in photosynthesis, central carbon metabolism, and nutrient cycling. While previous studies have focused on AMG diversity in the sunlit and dark ocean, less is known about the role of viruses in shaping metabolic networks along redox gradients associated with marine oxygen minimum zones (OMZs). Here, we analyzed relatively quantitative viral metagenomic datasets that profiled the oxygen gradient across Eastern Tropical South Pacific (ETSP) OMZ waters, assessing whether OMZ viruses might impact nitrogen (N) cycling via AMGs. Identified viral genomes encoded six N-cycle AMGs associated with denitrification, nitrification, assimilatory nitrate reduction, and nitrite transport. The majority of these AMGs (80%) were identified in T4-like Myoviridae phages, predicted to infect Cyanobacteria and Proteobacteria, or in unclassified archaeal viruses predicted to infect Thaumarchaeota. Four AMGs were exclusive to anoxic waters and had distributions that paralleled homologous microbial genes. Together, these findings suggest viruses modulate N-cycling processes within the ETSP OMZ and may contribute to nitrogen loss throughout the global oceans thus providing a baseline for their inclusion in the ecosystem and geochemical models.
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Affiliation(s)
- M. Consuelo Gazitúa
- grid.261331.40000 0001 2285 7943Department of Microbiology, The Ohio State University, Columbus, OH 43210 USA ,Viromica Consulting, Santiago, Chile
| | - Dean R. Vik
- grid.261331.40000 0001 2285 7943Department of Microbiology, The Ohio State University, Columbus, OH 43210 USA
| | - Simon Roux
- grid.451309.a0000 0004 0449 479XDOE Joint Genome Institute, Berkeley, CA USA
| | - Ann C. Gregory
- grid.261331.40000 0001 2285 7943Department of Microbiology, The Ohio State University, Columbus, OH 43210 USA
| | - Benjamin Bolduc
- grid.261331.40000 0001 2285 7943Department of Microbiology, The Ohio State University, Columbus, OH 43210 USA
| | - Brittany Widner
- grid.261368.80000 0001 2164 3177Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, VA USA ,grid.56466.370000 0004 0504 7510Woods Hole Oceanographic Institution, Woods Hole, MA USA
| | - Margaret R. Mulholland
- grid.261368.80000 0001 2164 3177Department of Ocean, Earth and Atmospheric Sciences, Old Dominion University, Norfolk, VA USA
| | - Steven J. Hallam
- grid.17091.3e0000 0001 2288 9830Department of Microbiology and Immunology, University of British Columbia, Vancouver, BC Canada
| | - Osvaldo Ulloa
- grid.5380.e0000 0001 2298 9663Departamento de Oceanografía & Instituto Milenio de Oceanografía, Universidad de Concepción, Concepción, Chile
| | - Matthew B. Sullivan
- grid.261331.40000 0001 2285 7943Department of Microbiology, The Ohio State University, Columbus, OH 43210 USA ,grid.261331.40000 0001 2285 7943Department of Civil, Environmental and Geodetic Engineering, The Ohio State University, Columbus, OH USA
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Kammel M, Hunger D, Sawers RG. The soluble cytoplasmic N-terminal domain of the FocA channel gates bidirectional formate translocation. Mol Microbiol 2020; 115:758-773. [PMID: 33169422 DOI: 10.1111/mmi.14641] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2020] [Revised: 11/05/2020] [Indexed: 11/28/2022]
Abstract
FocA belongs to the pentameric FNT (formate-nitrite transporter) superfamily of anion channels, translocating formate bidirectionally across the cytoplasmic membrane of Escherichia coli and other microorganisms. While the membrane-integral core of FocA shares considerable amino acid sequence conservation with other FNT family members, the soluble cytoplasmic N-terminal domain does not. To analyze the potential biochemical function of FocA's N-terminal domain in vivo, we constructed truncation derivatives and amino acid-exchange variants, and determined their ability to translocate formate across the membrane of E. coli cells by monitoring intracellular formate levels using a formate-sensitive reporter system. Analysis of strains synthesizing these FocA variants provided insights into formate efflux. Strains lacking the ability to generate formate intracellularly allowed us to determine whether these variants could import formate or its toxic chemical analog hypophosphite. Our findings reveal that the N-terminal domain of FocA is crucial for bidirectional FocA-dependent permeation of formate across the membrane. Moreover, we show that an amino acid sequence motif and secondary structural features of the flexible N-terminal domain are important for formate translocation, and efflux/influx is influenced by pyruvate formate-lyase. The soluble N-terminal domain is, therefore, essential for bidirectional formate translocation by FocA, suggesting a "gate-keeper" function controlling anion accessibility.
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Affiliation(s)
- Michelle Kammel
- Institute of Microbiology, Martin-Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Doreen Hunger
- Institute of Microbiology, Martin-Luther University Halle-Wittenberg, Halle (Saale), Germany
| | - Robert Gary Sawers
- Institute of Microbiology, Martin-Luther University Halle-Wittenberg, Halle (Saale), Germany
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Mukherjee M, Gupta A, Sankararamakrishnan R. Is the E. coli Homolog of the Formate/Nitrite Transporter Family an Anion Channel? A Computational Study. Biophys J 2020; 118:846-860. [PMID: 31968229 DOI: 10.1016/j.bpj.2019.12.024] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2019] [Revised: 12/04/2019] [Accepted: 12/16/2019] [Indexed: 10/25/2022] Open
Abstract
Formate/nitrite transporters (FNTs) selectively transport monovalent anions and are found in prokaryotes and lower eukaryotes. They play a significant role in bacterial growth and act against the defense mechanism of infected hosts. Because FNTs do not occur in higher animals, they are attractive drug targets for many bacterial diseases. Phylogenetic analysis revealed that they can be classified into eight subgroups, two of which belong to the uncharacterized YfdC-α and YfdC-β groups. Experimentally determined structures of FNTs belonging to different phylogenetic groups adopt the unique aquaporin-like hourglass helical fold. We considered the formate channel from Vibrio cholerae, the hydrosulphide channel from Clostridium difficile, and the uncharacterized channel from Escherichia coli (EcYfdC) to investigate the mechanism of transport and selectivity. Using equilibrium molecular dynamics and umbrella sampling studies, we determined temporal channel radius profiles, permeation events, and potential of mean force profiles of different substrates with the conserved central histidine residue in protonated or neutral form. Unlike the formate channel from V. cholerae and the hydrosulphide channel from C. difficile, molecular dynamics studies showed that the formate substrate was unable to enter the vestibule region of EcYfdC. Absence of a conserved basic residue and presence of acidic residues in the vestibule regions, conserved only in YfdC-α, were found to be responsible for high energy barriers for the anions to enter EcYfdC. Potential of mean force profiles generated for ammonia and ammonium ion revealed that EcYfdC can transport neutral solutes and could possibly be involved in the transport of cations analogous to the mechanism proposed for ammonium transporters. Although YfdC members belong to the FNT family, our studies strongly suggest that EcYfdC is not an anion channel. Absence or presence of specific charged residues at particular positions makes EcYfdC selective for neutral or possibly cationic substrates. Further experimental studies are needed to get a definitive answer to the question of the substrate selectivity of EcYfdC. This provides an example of membrane proteins from the same family transporting substrates of different chemical nature.
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Affiliation(s)
- Mishtu Mukherjee
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology Kanpur, Kanpur, India
| | - Ankita Gupta
- Department of Biological Sciences and Bioengineering, Indian Institute of Technology Kanpur, Kanpur, India
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