Electrobiocorrosion by microbes without outer-surface cytochromes

Anaerobic microbial corrosion of iron-containing metals causes extensive economic damage.Some microbes are capable of direct metal-to-microbe electron transfer(electrobiocorrosion),but the prevalence of electrobiocorrosion among diverse methanogens and acetogens is poorly understood because of a lack of tools for their genetic manipulation.Previous studies have suggested that respiration with 316L stainless steel as the electron donor is indicative of electrobiocorrosion,because,unlike pure Fe^(0),316L stainless steel does not abiotically generate H_(2) as an intermediary electron carrier.Here,we report that all of the methanogens(Methanosarcina vacuolata,Methanothrix soehngenii,and Methanobacterium strain IM1)and acetogens(Sporomusa ovata and Clostridium ljungdahli)evaluated respired with pure Fe^(0)as the electron donor,but only M.vacuolata,Mx.soehngeni,and S.ovata were capable of stainless steel electrobiocorrosion.The electrobiocorrosive methanogens re-quired acetate as an additional energy source in order to produce methane from stainless steel.Cocultures of S.ovata and Mx.soehngeni demonstrated how acetogens can provide acetate to methanogens during corrosion.Not only was Meth-anobacterium strain IM1 not capable of electrobiocorrosion,but it also did not accept electrons from Geobacter metal-lireducens,an effective electron-donating partner for direct interspecies electron transfer to all methanogens that can directly accept electrons from Fe^(0).The finding that M.vacuolata,Mx.soehngeni,and S.ovata are capable of electrobiocorrosion,despite a lack of the outer-surface c-type cytochromes previously found to be important in other electrobiocorrosive microbes,demonstrates that there are multiple microbial strategies for making electrical contact with Fe^(0).

Microbial diversity and oil biodegradation potential of northern Barents Sea sediments

The Arctic,an essential ecosystem on Earth,is subject to pronounced anthropogenic pressures,most notable being the climate change and risks of crude oil pollution.As crucial elements of Arctic environments,benthic microbiomes are involved in climate-relevant biogeochemical cycles and hold the potential to remediate upcoming contamination.Yet,the Arctic benthic microbiomes are among the least explored biomes on the planet.Here we combined geochemical analyses,incubation experiments,and microbial community profiling to detail the biogeography and biodegradation potential of Arctic sedimentary microbiomes in the northern Barents Sea.The results revealed a predominance of bacterial and archaea phyla typically found in the deep marine biosphere,such as Chloroflexi,Atribacteria,and Bathyarcheaota.The topmost benthic communities were spatially structured by sedimentary organic carbon,lacking a clear distinction among geographic regions.With increasing sediment depth,the community structure exhibited stratigraphic variability that could be correlated to redox geochemistry of sediments.The benthic microbiomes harbored multiple taxa capable of oxidizing hydrocarbons using aerobic and anaerobic pathways.Incubation of surface sediments with crude oil led to proliferation of several genera from the so-called rare biosphere.These include Alkalimarinus and Halioglobus,previously unrecognized as hydrocarbon-degrading genera,both harboring the full genetic potential for aerobic alkane oxidation.These findings increase our understanding of the taxonomic inventory and functional potential of unstudied benthic microbiomes in the Arctic.