Biology subjects

Lovley, D.

Publications and source records attributed to Lovley, D..

4 recordsLinked to original sources

bioRxiv2024

Medium Composition Affects Microbial Corrosion Rates

Desulfovibrio vulgaris and Desulfovibrio ferrophilus were previously proposed to have distinct iron corrosion mechanisms because D. ferrophilus corroded faster. However, the chloride concentration in the D. ferrophilus marine medium was much higher than in the D. vulgaris freshwater medium. D. vulgaris corrosion rates accelerated with increasing chloride and were faster than D. ferrophilus in the same marine medium. Differences in D. ferrophilus corrosion rates in two different media with the same chloride concentration suggested that minor differences in other medium constituents also impact on microbial corrosion. These results demonstrate the importance of considering medium composition in microbial corrosion studies.

microbiology↗

bioRxiv2022

Different Routes for Direct Interspecies Electron Transfer with Diverse Electron-Accepting Partners

Direct interspecies electron transfer (DIET) may be most important in methanogenic environments, but studies to date that have examined the mechanisms for electron transfer from electron-donating partners have primarily focused on co-cultures in which fumarate was the terminal electron acceptor. To better understand DIET with methanogens, the transcriptome of Geobacter metallireducens during DIET-based growth with Geobacter sulfurreducens reducing fumarate was compared with the transcriptome of G. metallireducens grown in co-culture with diverse Methanosarcina species. The transcriptome of G. metallireducens co-cultured with G. sulfurreducens was significantly different from those with Methanosarcina. Furthermore, the transcriptome of G. metallireducens grown with Methanosarcina barkeri, which lacks outer-surface cytochromes, was different from the transcriptome of G. metallireducens co-cultured with Methanosarcina acetivorans or Methanosarcina subterranea, which have an outer-surface c-type cytochrome that serves as an electrical connect for DIET. Differences in G. metallireducens expression patterns for c-type cytochrome genes were particularly notable. The impact of deleting G. metallireducens c-type cytochrome genes depended upon the electron-accepting partner. Multiple cytochromes that G. metallireducens required for DIET with G. sulfurreducens and for Fe(III) oxide reduction were not required for DIET with the Methanosarcina species. Porin-cytochrome complexes and e-pili were required for optimal DIET with all partners. 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 cytochromes does not necessarily confer the capacity for DIET, and also emphasize the substantial impact of the physiology of the electron-accepting partner on the physiology of the electron-donating DIET partner.

microbiology↗

bioRxiv2021

Mechanisms for Electron Uptake by Methanosarcina acetivorans During Direct Interspecies Electron Transfer

Direct interspecies electron transfer (DIET) between bacteria and methanogenic archaea appears to be an important syntrophy in both natural and engineered methanogenic environments. However, the electrical connections on the outer surface of methanogens and the subsequent processing of electrons for carbon dioxide reduction to methane are poorly understood. Here we report that the genetically tractable methanogen Methanosarcina acetivorans can grow via DIET in co-culture with Geobacter metallireducens serving as the electron-donating partner. Comparison of gene expression patterns in M. acetivorans grown in co-culture versus pure culture growth on acetate revealed that transcripts for the outer-surface, multi-heme, c-type cytochrome MmcA were higher during DIET-based growth. Deletion of mmcA inhibited DIET. The high aromatic amino acid content of M. acetivorans archaellins suggests that they might assemble into electrically conductive archaella. A mutant that could not express archaella was deficient in DIET. However, this mutant grew in DIET-based co-culture as well as the archaella-expressing parental strain in the presence of granular activated carbon, which was previously shown to serve as a substitute for electrically conductive pili as a conduit for long-range interspecies electron transfer in other DIET-based co-cultures. Transcriptomic data suggesting that the membrane-bound Rnf, Fpo, and HdrED complexes also play a role in DIET were incorporated into a charge-balanced model illustrating how electrons entering the cell through MmcA can yield energy to support growth from carbon dioxide reduction. The results are the first genetics-based functional demonstration of likely outer-surface electrical contacts for DIET in a methanogen. ImportanceThe conversion of organic matter to methane plays an important role in the global carbon cycle and is an effective strategy for converting wastes to a useful biofuel. The reduction of carbon dioxide to methane accounts for approximately a third of the methane produced in anaerobic soils and sediments as well as waste digesters. Potential electron donors for carbon dioxide reduction are H2 or electrons derived from direct interspecies electron transfer (DIET) between bacteria and methanogens. Elucidating the relative importance of these electron donors has been difficult due to a lack of information on the electrical connects on the outer surface of methanogens and how they process the electrons received from DIET. Transcriptomic patterns and gene deletion phenotypes reported here provide insight into how a group of Methanosarcina that play an important role in methane production in soils and sediments participate in DIET.

microbiology↗

bioRxiv2019

A Membrane-Bound Cytochrome Enables Methanosarcina acetivorans to Conserve Energy to Support Growth from Extracellular Electron Transfer

Conservation of energy to support growth solely from extracellular electron transfer was demonstrated for the first time in a methanogen. Methanosarcina acetivorans grew with methanol as the sole electron donor and the extracellular electron acceptor anthraquione-2,6-disulfonate (AQDS) as the sole electron acceptor when methane production was inhibited with bromoethanesulfonate. Transcriptomics revealed that transcripts for the gene for the transmembrane, multi-heme, c-type cytochrome MmcA were 4-fold higher in AQDS-respiring cells versus methanogenic cells. A strain in which the gene for MmcA was deleted failed to grow via AQDS reduction whereas strains in which other cytochrome genes were deleted grew as well as the wild-type strain. The MmcA-deficient strain grew with the conversion of methanol or acetate to methane, suggesting that MmcA has a specialized role as a conduit for extracellular electron transfer. Enhanced expression of genes for methanol conversion to methyl-coenzyme M and components of the Rnf complex suggested that methanol is oxidized to carbon dioxide in AQDS-respiring cells through a pathway that is similar to methyl-coenezyme M oxidation in methanogenic cells. However, during AQDS respiration the Rnf complex and reduced methanophenazine probably transfer electrons to MmcA, which functions as the terminal reductase for AQDS reduction. Extracellular electron transfer may enable survival of methanogens in dynamic environments in which oxidized humic substances and Fe(III) oxides are intermittently available. The availability of tools for genetic manipulation of M. acetivorans makes it an excellent model microbe for evaluating c-type cytochrome-dependent extracellular electron transfer in Archaea.\n\nImportanceExtracellular electron exchange in Methanosarcina species and closely related Archaea plays an important role in the global carbon cycle and can enhance the speed and stability of anaerobic digestion, an important bioenergy strategy. The potential importance of c-type cytochromes for extracellular electron transfer to syntrophic bacterial partners and/or Fe(III) minerals in some Archaea has been suspected for some time, but the studies with Methanosarcina acetivorans reported here provide the first genetic evidence supporting this hypothesis. The results suggest parallels with Gram-negative bacteria, such as Shewanella and Geobacter species, in which outer-surface c-type cytochromes are an essential component for electrical communication with the extracellular environment. M. acetivorans offers an unprecedented opportunity to study mechanisms for energy conservation from the anaerobic oxidation of one-carbon organic compounds coupled to extracellular electron transfer in Archaea with implications not only for methanogens, but possibly also for anaerobic methane oxidation.

microbiology↗