Biology subjects

Lovley, D. R.

Publications and source records attributed to Lovley, D. R..

3 recordsLinked to original sources

bioRxiv2017

Potential for Methanosarcina to contribute to uranium reduction during acetate-promoted groundwater bioremediation

Previous studies of in situ bioremediation of uranium-contaminated groundwater with acetate injections have focused on the role of Geobacter species in U(VI) reduction because of a lack of other abundant known U(VI)-reducing microorganisms. Monitoring the levels of methyl CoM reductase subunit A (mcrA) transcripts during an acetate-injection field experiment demonstrated that acetoclastic methanogens from the genus Methanosarcina were enriched after 40 days of acetate amendment. The increased abundance of Methanosarcina corresponded with an accumulation of methane in the groundwater. An enrichment culture dominated by a Methanosarcina species with the same Methanosarcina mcrA sequence that predominated in the field experiment could effectively convert acetate to methane. In order to determine whether Methanosarcina species could be participating in U(VI) reduction in the subsurface, cell suspensions of M. barkeri were incubated in the presence of U(VI) with acetate provided as the electron donor. U(VI) was reduced by metabolically active M. barkeri cells, however, no U(VI) reduction was observed in inactive controls. These results demonstrate that Methanosarcina species could play an important role in the long-term bioremediation of uranium-contaminated aquifers after depletion of Fe(III) oxides limits the growth of Geobacter species. The results also suggest that Methanosarcina have the potential to influence uranium geochemistry in a diversity of anaerobic sedimentary environments.

microbiology↗

bioRxiv2017

Electrically Conductive Pili from Pilin Genes of Phylogenetically Diverse Microorganisms

The possibility that bacteria other than Geobacter species might contain genes for electrically conductive pili (e-pili) was investigated by heterologously expressing pilin genes of interest in Geobacter sulfurreducens. Strains of G. sulfurreducens producing high current densities, which are only possible with e-pili, were obtained with pilin genes from Flexistipes sinusarabici, Calditerrivibrio nitroreducens, and Desulfurivibrio alkaliphilus. The conductance of pili from these strains was comparable to native G. sulfurreducens e-pili. The e-pili derived from C. nitroreducens, and D. alkaliphilus pilin genes are the first examples of relatively long (> 100 amino acids) pilin monomers assembling into e-pili. The pilin gene from Desulfofervidus auxilii did not yield e-pili, suggesting that the hypothesis that this sulfate reducer wires itself to ANME-1 microbes with e-pili to promote anaerobic methane oxidation should be reevaluated. A high density of aromatic amino acids and a lack of substantial aromatic-free gaps along the length of long pilins may be important characteristics leading to e-pili. This study demonstrates a simple method to screen pilin genes from difficult-to-culture microorganisms for their potential to yield e-pili; reveals new potential sources for biologically based electronic materials; and suggests that a wide phylogenetic diversity of microorganisms may employ e-pili for extracellular electron exchange.

microbiology↗

bioRxiv2017

Improper Localization of the OmcS Cytochrome May Explain the Inability of the xapD-Deficient Mutant of Geobacter sulfurreducens to Reduce Fe(III) Oxide

Extracellular electron transfer through a redox-active exopolysaccharide matrix has been proposed as a strategy for extracellular electron transfer to Fe(III) oxide by Geobacter sulfurreducens, based on the phenotype of a xapD-deficient strain. Central to this model was the assertion that the xapD-deficient strain produced pili decorated with the multi-heme c-type cytochrome OmcS in manner similar to the wild-type strain. Further examination of the xapD-deficient strain with immunogold labeling of OmcS and transmission electron microscopy revealed that OmcS was associated with the outer cell surface rather than pili. PilA, the pilus monomer, could not be detected in the xapD-deficient strain under conditions in which it was readily detected in the wild-type strain. Multiple lines of evidence in previous studies have suggested that long-range electron transport to Fe(III) oxides proceeds through electrically conductive pili and that OmcS associated with the pili is necessary for electron transfer from the pili to Fe(III) oxides. Therefore, an alternative explanation for the Fe(III) oxide reduction phenotype of the xapD-deficient strain is that the pili-OmcS route for extracellular electron transport to Fe(III) oxide has been disrupted in the xapD-deficient strain.

microbiology↗