Microbiology Study In Glacial Foreland In East Antarctica And Piezophile Study From Earth's Surface

Cryosphere is important and covers 11%of earth land surface,including ice sheet in Antarctic,polythermal glaciers in Arctic,sea ice in Arctic ocean,and Alpine glacier in mountains.Deglaciation in polar region affects earth ecosystem more and more because of climate change.Despite the extreme condition here,various microbes inhabit and metabolize in supraglacier,englacial crevasses,subglacier and subglacial lake.Considering the global warming fact,condition change during the deglaciation could influence the microbial community,activity and element cycling.However,how the microbial community structure and acitivty in icesheet margin sediment were affected is unknown.Especially beneath the Antarctic ice sheet,the community adaptation to climate change and the effect of temperature and nutrient on methane production were unknown due to the difficult sampling and study in extreme Antarctic condition.The gap in the knowledge make it difficult to predict the community change and carbon budget beneath ice sheet.In this study,soil samples were collected from the East Antarctic Icesheet margin,the window of subglacial ecosystem,and these questions were researched here:1)How does the bacterial community response to the deglaciation in glacial foreland?2)How does the methanogenesis in subglacial sediment response to the temperature and substrate change?At the community structure level,the bacterial communities including abundant and rare bacteria groups,which developed at the initial stage of deglaciation in the foreland of the East Antarctica ice sheet in Larsemann Hills,was characterized using the Miseq sequencing method.Abundant bacteria contribute d more to the structure of community and were more sensitive to changes in conditions than were the rare bacteria.Moreover,among the environmental parameters tested,which included total organic carbon,pH,and moisture of the soils,ice thickness was the most influential factor affecting the community structure of abundant bacteria according to the correlation analysis.What is more,the key players,including taxon belong to Actinobacteria,Verrucomicrobia and Gammaproteobacteria,were mostly affected during the early stages of deglaciation in the glacier foreland.With these results,the mechanisms that drive the evolution of bacterial communities at the foreland of a glacier in Antarctica could be further identified,and therefore,the response of the microbial community to climate change can be predicted with more certainty in this polar region.At the methane production acitivity level,the subglacial sediment from East Antarctic ice sheet near to Larsemann Hills was collected and incubated in lab for 7months with different temperatures and substrates.Methane was produced as fast as 398 pmol/day/gram in 1 ^oC with H₂ supplied.Moreover,increased temperature influenced the methanogenesis in the subglacial sediment.Methanomicrobiales,the hydrogen-consuming methanogens,were dominant in the sample before and after the long incubation period by analyzing clone library.The mcrA gene copy number in the original subglacial sediment was 2.3×10⁴ copies/g.With supplied H₂+CO₂,a greater than 300-fold increase was observed at all temperatures.The bacterial community in the original subglacial sediment was analyzed using Miseq sequencing method.4.5%of the bacterial community including Clostridium can potentially produce hydrogen and support the hydrogenotropic methanogenesis in East Antarctic subglacial sediment.Moreover,genes related to hydrogenotropic methanogenesis were found in the metagenomic data from original sediment and hydrogen-supplied culture.Based on the community structure and activity analysis,methane production model in East Antarctic subglacial sediment was proposed.Methane production rate in subglacial sediment and permafrost on earth was estimated and endogenic methanogenetic rate in subglacial sediment was 10¹-10⁴pmol/gram/day.Therefore,hydrogenotrophic methanogenesis was inferred as the primary methane-producing pathway,and the hydrogenotrophic methanogens therein might have been well-adapted to the cold environment.These findings highlight the effects of temperature and substrate on methanogenesis in the subglacial sediment of East Antarctica,improving the estimations of global methane budget.In conclusion,the study showed that microbial community structure and activity could be affected by increased temperature or deglaciation in East Antarctic ice sheet margin.At the community structure level,abundant bacteria were affected by ice thickness and rare bacteria were important for stabilizing community structure,suggesting the effect of deglaciation on microbial metabolic potential in glacial foreland.These results are helpful on the understanding about soil development in glacial foreland and on predicting community development caused by climate change.Moreover,testing the response of methanogenesis to different temperatures and substrates showed the global warming's effect on carbon cycling in polar region at the activity level.The finding also provided more data on microbe adaptation to low temperture.In summary,this study highlights the interaction between climate change and microbial community structure and activity in polar.Meanwhile,high pressure is another key factor beneath ice sheet besides the low temperature.High pressure can influences microbial metabolism.Here we study piezophile from other environment,considering no piezophile was found beneath ice sheet.Piezophile,including fungus,archaea and bacteria,grows better under high pressure than at ambient condition and found from deep biosphere like deep sea.Deep biosphere is essential for the origin of life in early earth and is important in present earth representing half of the prokaryotes on Earth.Research about the isolated piezophile and development of HHP?high hydrostatic pressure?sampling equipment and cultivation devices has last for decades.However,how the piezophilic character was kept or lost is still unknown.Isolated piezophile were few compared with all isolated strains in earth and just in a few genera including Shewanella,Photobctrium,Colwellia,Moritella,Psychromonas.Here,this study was focused on these questions:1)Is depth at origin really essential for hydrostatic pressure preference?2)What is the relationship between piezophilic character and other factors?The materials were two bacillus from earth surface environment,Sporosarcina psychrophila DSM 6497 and Lysinibacillus sphaericus LMG 22257.Both of them can mediate calcium carbonate precipitation under high pressure.in this study,we found the two strains were piezophiles with optimal pressure 7 MPa and 20 MPa respectively for S.psychrophila DSM 6497 and L.sphaericus LMG 22257.S.psychrophila DSM 6497 was isolated from soil and river in earth surface.L.sphaericus LMG 22257 was isolated from bioreactor.The phylogenetic tree based on their 16S rRNA gene showed that the closest sequences were also from earth surface.Both of the strains were Gram-positive,spore-formation piezophiles.This is the first report about the ambient condition-derived piezophilie.The finding extends the diversity and isolation source of piezophile.Moreover,at their optimal pressures for growth their temperature and salinity ranges widened relative to those existing under ambient conditions.The optimal pH for the two strains was lower at optimal pressure than that at ambient pressure.These findings suggest that HHP affects cell globally and associated with other factors.What is more,the two strains grew better at optimal pressure than at ambient pressure under the chaotropic stress of Mg²⁺?<250mM?,while high concentration of Mg²⁺stimulates their growth under 50 MPa.These results showed the correlation between HHP and chaotropic stress adaptation.Comparative proteomic analysis was performed to study the HHP and chaotropic stress adaptation.Firstly the complete genomes of the two strains were sequenced with Miseq sequencing method and s ingle-molecule real-time?SMRT?sequencing method.After the assembling and annotation,the potential metabolic pathways were predicted.Then S.psychrophila DSM 6497 was cultured in chaotropic solution under 0.1 and 7 MPa.The proteomic were analyzed comparatively.The cellular morphology was observed with TEM?transmission electron microscope?.Cell was more mummified in chaotropic solution under 0.1 MPa compared wit h that under 7 MPa.The proteomic data showed that chaotropic stress influenced the protein synthesis,posttranslational modification,vesicle transport and secretion,energy production and conversion,suggesting the comprehensive harmful to cell by chaotropic solution.However,HHP affected the energy production and conversion,secretion and transport,inorganic ions transport processes.Lots of the proteins under HHP were regulated in the opposite direction compared with chaotropic stress.The proteomic data directly show how high pressure releases the cell from growth boundary of chaotropic stress and vise versa.In conclusion,finding piezophile from ambient condition extends the diversity and isolation source of piezophile,and demonstrates that the distribution of piezophiles is not constrained to pressurized conditions,but other factors like Mg²⁺stress.These results showed that significance of metabolism under high pressure could be more important than expected before,provided the new materials for the study of piezophilic mechanism,provided new strategy for isolation piezophile.This could also be one of the key proof for the hypothesis that life origined under high pressure condition.