@article {3085, title = {Potential for Methanosarcina to Contribute to Uranium Reduction during Acetate-Promoted Groundwater Bioremediation.}, journal = {Microb Ecol}, volume = {76}, year = {2018}, month = {2018 Oct}, pages = {660-667}, abstract = {

Previous studies of acetate-promoted bioremediation of uranium-contaminated aquifers focused on Geobacter because no other microorganisms that can couple the oxidation of acetate with U(VI) reduction had been detected in situ. 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. In order to determine whether Methanosarcina species could be participating in U(VI) reduction in the subsurface, cell suspensions of Methanosarcina 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.

}, keywords = {Acetates, Biodegradation, Environmental, Geobacter, Groundwater, Methane, Methanosarcina, Oxidation-Reduction, Uranium, Water Pollutants, Chemical}, issn = {1432-184X}, doi = {10.1007/s00248-018-1165-5}, author = {Holmes, Dawn E and Orelana, Roberto and Giloteaux, Ludovic and Wang, Li-Ying and Shrestha, Pravin and Williams, Kenneth and Lovley, Derek R and Rotaru, Amelia-Elena} } @article {3134, title = {Syntrophic growth with direct interspecies electron transfer as the primary mechanism for energy exchange.}, journal = {Environ Microbiol Rep}, volume = {5}, year = {2013}, month = {2013 Dec}, pages = {904-10}, abstract = {

Direct interspecies electron transfer (DIET) through biological electrical connections is an alternative to interspecies H2 transfer as a mechanism for electron exchange in syntrophic cultures. However, it has not previously been determined whether electrons received via DIET yield energy to support cell growth. In order to investigate this, co-cultures of Geobacter metallireducens, which can transfer electrons to wild-type G. sulfurreducens via DIET, were established with a citrate synthase-deficient G. sulfurreducens strain that can receive electrons for respiration through DIET only. In a medium with ethanol as the electron donor and fumarate as the electron acceptor, co-cultures with the citrate synthase-deficient G. sulfurreducens strain metabolized ethanol as fast as co-cultures with wild-type, but the acetate that G. metallireducens generated from ethanol oxidation accumulated. The lack of acetate metabolism resulted in less fumarate reduction and lower cell abundance of G. sulfurreducens. RNAseq analysis of transcript abundance was consistent with a lack of acetate metabolism in G. sulfurreducens and revealed gene expression levels for the uptake hydrogenase, formate dehydrogenase, the pilus-associated c-type cytochrome OmcS and pili consistent with electron transfer via DIET. These results suggest that electrons transferred via DIET can serve as the sole energy source to support anaerobic respiration.

}, keywords = {Acetates, Anaerobiosis, Citrate (si)-Synthase, Cytochrome c Group, Electron Transport, Electrons, Energy Metabolism, Ethanol, Fimbriae, Bacterial, Formate Dehydrogenases, Fumarates, Geobacter, Oxidation-Reduction}, issn = {1758-2229}, doi = {10.1111/1758-2229.12093}, author = {Shrestha, Pravin Malla and Rotaru, Amelia-Elena and Aklujkar, Muktak and Liu, Fanghua and Shrestha, Minita and Summers, Zarath M and Malvankar, Nikhil and Flores, Dan Carlo and Lovley, Derek R} } @article {3146, title = {Transcriptomic and genetic analysis of direct interspecies electron transfer.}, journal = {Appl Environ Microbiol}, volume = {79}, year = {2013}, month = {2013 Apr}, pages = {2397-404}, abstract = {

The possibility that metatranscriptomic analysis could distinguish between direct interspecies electron transfer (DIET) and H2 interspecies transfer (HIT) in anaerobic communities was investigated by comparing gene transcript abundance in cocultures in which Geobacter sulfurreducens was the electron-accepting partner for either Geobacter metallireducens, which performs DIET, or Pelobacter carbinolicus, which relies on HIT. Transcript abundance for G. sulfurreducens uptake hydrogenase genes was 7-fold lower in cocultures with G. metallireducens than in cocultures with P. carbinolicus, consistent with DIET and HIT, respectively, in the two cocultures. Transcript abundance for the pilus-associated cytochrome OmcS, which is essential for DIET but not for HIT, was 240-fold higher in the cocultures with G. metallireducens than in cocultures with P. carbinolicus. The pilin gene pilA was moderately expressed despite a mutation that might be expected to repress pilA expression. Lower transcript abundance for G. sulfurreducens genes associated with acetate metabolism in the cocultures with P. carbinolicus was consistent with the repression of these genes by H2 during HIT. Genes for the biogenesis of pili and flagella and several c-type cytochrome genes were among the most highly expressed in G. metallireducens. Mutant strains that lacked the ability to produce pili, flagella, or the outer surface c-type cytochrome encoded by Gmet_2896 were not able to form cocultures with G. sulfurreducens. These results demonstrate that there are unique gene expression patterns that distinguish DIET from HIT and suggest that metatranscriptomics may be a promising route to investigate interspecies electron transfer pathways in more-complex environments.

}, keywords = {Acetates, Deltaproteobacteria, Electron Transport, Hydrogen, Metabolic Networks and Pathways, Transcriptome}, issn = {1098-5336}, doi = {10.1128/AEM.03837-12}, author = {Shrestha, Pravin Malla and Rotaru, Amelia-Elena and Summers, Zarath M and Shrestha, Minita and Liu, Fanghua and Lovley, Derek R} }