Discovery of anaerobic lithoheterotrophic haloarchaea, ubiquitous in hypersaline habitats

Hypersaline anoxic habitats harbour numerous novel uncultured archaea whose metabolic and ecological roles remain to be elucidated. Until recently, it was believed that energy generation via dissimilatory reduction of sulfur compounds is not functional at salt saturation conditions. Recent discovery of the strictly anaerobic acetotrophic Halanaeroarchaeum compels to change both this assumption and the traditional view on haloarchaea as aerobic heterotrophs. Here we report on isolation and characterization of a novel group of strictly anaerobic lithoheterotrophic haloarchaea, which we propose to classify as a new genus Halodesulfurarchaeum. Members of this previously unknown physiological group are capable of utilising formate or hydrogen as electron donors and elemental sulfur, thiosulfate or dimethylsulfoxide as electron acceptors. Using genome-wide proteomic analysis we have detected the full set of enzymes required for anaerobic respiration and analysed their substrate-specific expression. Such advanced metabolic plasticity and type of respiration, never seen before in haloarchaea, empower the wide distribution of Halodesulfurarchaeum in hypersaline inland lakes, solar salterns, lagoons and deep submarine anoxic brines. The discovery of this novel functional group of sulfur-respiring haloarchaea strengthens the evidence of their possible role in biogeochemical sulfur cycling linked to the terminal anaerobic carbon mineralisation in so far overlooked hypersaline anoxic habitats.</p

Evidence of in situ microbial activity and sulphidogenesis in perennially sub-0 \ub0C and hypersaline sediments of a high Arctic permafrost spring

The lost hammer (LH) spring perennially discharges subzero hypersaline reducing brines through thick layers of permafrost and is the only known terrestrial methane seep in frozen settings on Earth. The present study aimed to identify active microbial communities that populate the sediments of the spring outlet, and verify whether such communities vary seasonally and spatially. Microcosm experiments revealed that the biological reduction of sulfur compounds (SR) with hydrogen (e.g., sulfate reduction) was potentially carried out under combined hypersaline and subzero conditions, down to 1220 \ub0C, the coldest temperature ever recorded for SR. Pyrosequencing analyses of both 16S rRNA (i.e., cDNA) and 16S rRNA genes (i.e., DNA) of sediments retrieved in late winter and summer indicated fairly stable bacterial and archaeal communities at the phylum level. Potentially active bacterial and archaeal communities were dominated by clades related to the T78 Chloroflexi group and Halobacteria species, respectively. The present study indicated that SR, hydrogenotrophy (possibly coupled to autotrophy), and short-chain alkane degradation (other than methane), most likely represent important, previously unaccounted for, metabolic processes carried out by LH microbial communities. Overall, the obtained findings provided additional evidence that the LH system hosts active communities of anaerobic, halophilic, and cryophilic microorganisms despite the extreme conditions in situ.Peer reviewed: YesNRC publication: Ye

Defining the functional potential and active community members of a sediment microbial community in a high-arctic hypersaline subzero spring

The Lost Hammer (LH) Spring is the coldest and saltiest terrestrial spring discovered to date and is characterized by perennial discharges at subzero temperatures (-5\ub0C), hypersalinity (salinity, 24%), and reducing ( 48-165mV), microoxic, and oligotrophic conditions. It is rich in sulfates (10.0%, wt/wt), dissolved H2S/sulfides (up to 25ppm), ammonia ( 48381\u3bcM), and methane (11.1g day-1). To determine its total functional and genetic potential and to identify its active microbial components, we performed metagenomic analyses of the LH Spring outlet microbial community and pyrosequencing analyses of the cDNA of its 16S rRNA genes. Reads related to Cyanobacteria (19.7%), Bacteroidetes (13.3%), and Proteobacteria (6.6%) represented the dominant phyla identified among the classified sequences. Reconstruction of the enzyme pathways responsible for bacterial nitrification/ denitrification/ammonification and sulfate reduction appeared nearly complete in the metagenomic data set. In the cDNA profile of the LH Spring active community, ammonia oxidizers (Thaumarchaeota), denitrifiers (Pseudomonas spp.), sulfate reducers (Desulfobulbus spp.), and other sulfur oxidizers (Thermoprotei) were present, highlighting their involvement in nitrogen and sulfur cycling. Stress response genes for adapting to cold, osmotic stress, and oxidative stress were also abundant in the metagenome. Comparison of the composition of the functional community of the LH Spring to metagenomes from other saline/ subzero environments revealed a close association between the LH Spring and another Canadian high-Arctic permafrost environment, particularly in genes related to sulfur metabolism and dormancy. Overall, this study provides insights into the metabolic potential and the active microbial populations that exist in this hypersaline cryoenvironment and contributes to our understanding of microbial ecology in extreme environments. \ua9 2013, American Society for Microbiology.Peer reviewed: YesNRC publication: Ye

Export of Organic Matter and Microbes from the Greenland Ice Sheet: Sources, Composition, and Downstream Implications

Meltwater runoff from the Greenland Ice Sheet (GrIS) has increased by more than 50% in the last 50 years. While considerable uncertainty revolves around the impact this change may have on downstream ecosystems, previous research has suggested that solute and microbial exports from the GrIS are likely to increase with higher freshwater fluxes. We monitored the Watson River, a glacially fed river in West Greenland, over the 2012 and 2015 summers to evaluate the influence increased fluxes may exert on local microbial communities and downstream biogeochemical cycles. Our objectives were to approximate the number of cells exported, characterize cell assemblages, and determine their origin. In 2012, paired microbiological samples were taken sporadically at the Leverett Glacier meltwater portal (at the head of the Watson River) and the Watson River fjord outlet 30 km downstream, to quantify microbial cells and characterize assemblage structure. We found cell concentrations and microbial assemblages to be very similar between locations, despite their distance apart. This suggests that GrIS outlet rivers are "neutral pipes" connecting microbes between glacial and estuarine habitats. We further identified subtle shifts in assemblage structure over the course of the summer melt season (May to August), and hypothesized that this reflects an expanding subglacial drainage network, with waters draining parts of the GrIS bed progressively further inland as the melt season progressed. Meltwaters from the Leverett Glacier portal were again monitored during the 2015 summer to identify the source of exported microbes by sampling during or near outburst events, which flush long-term stored waters from the ice-sheet bed. Using 14C dating, we found that exported suspended sediment-bound carbon becomes progressively older from June to August. This suggests that different reservoirs are tapped as the melt season progresses, which we interpret as originating from a greater distance into the GrIS subglacial environment. While further exploration is necessary to evaluate the long-term consequences of deglaciation, this work provides new and interesting information on glacial exports to downstream ecosystems and insights into their associated biogeochemical cycles

Rock comminution as a source of hydrogen for subglacial ecosystems

Substantial parts of the beds of glaciers, ice sheets and ice caps are at the pressure melting point1. The resulting water harbours diverse subglacial microbial ecosystems2, 3 capable of affecting global biogeochemical cycles4, 5. Such subglacial habitats may have acted as refugia during Neoproterozoic glaciations6. However, it is unclear how life in subglacial environments could be supported during glaciations lasting millions of years because energy from overridden organic carbon would become increasingly depleted7, 8. Here we investigate the potential for abiogenic H2 produced during rock comminution to provide a continual source of energy to support subglacial life. We collected a range of silicate rocks representative of subglacial environments in Greenland, Canada, Norway and Antarctica and crushed them with a sledgehammer and ball mill to varying surface areas. Under an inert atmosphere in the laboratory, we added water, and measured H2 production with time. H2 was produced at 0 °C in all silicate–water experiments, probably through the reaction of water with mineral surface silica radicals formed during rock comminution. H2 production increased with increasing temperature or decreasing silicate rock grain size. Sufficient H2 was produced to support previously measured rates of methanogenesis under a Greenland glacier. We conclude that abiogenic H2 generation from glacial bedrock comminution could have supported life and biodiversity in subglacial refugia during past extended global glaciations