The Study Of Microbial Community Diversity, Microbial Succession, And Bacterial Sources In The Fildes Region, Maritime Antactica

Microbial biogeography is the ecological theme of researching the spatial and temporal distribution of microbial diversity,and microbial succession is for studying the changes of microbial community over time and how they colonized in a new environment.Both of them are the fundamental issues of microbial ecology.Antarctic,the southernmost continent of the earth,has relatively simple ecological structure,and microorganisms are the core drivers of the element and nutrient cycle in this extreme environment.Low temperature,oligotrophy and less human activity make the Antarctic region a unique place to study the distribution and succession of microbial communitie.This region has undergone multiple geologic and glacial events in history,forming the geological features mainly consisted of the Tertiary volcanic rock and the Holocene raised beach.During the period from 2013 to 2015,the scientific research expediton consisted of the scientists form Institute of Botany of the Chinese Academy of Sciences,Shandong University and Wuhan University established 12 permanent quadrots around the Fields Region,maritime antarctcia,to study the long-term feedback of vegetation?moss,lichens?and microbial communities on climate change.Therefore,in this thesis,our takes were to study the distribution and succession of microbial microorganisms in the Fildes Region,maritime Antarctica,and explores new microbial resources and functions.First,using high-throughput sequencing and PLFA methods studied the diversity of microbial communities in these 12 quadrots and the communities were divided into two groups according to the soil elemental compositions and environmental attributes of Holocene raised beach and Tertiary volcanic stratigraphy.The dominant bacteria in these quadrots were Actinobacteria?24.2%?,Acidobacteria?14.7%?,Proteobacteria?15.1%?,Chloroflexi?12.3%?,and Gemmatimonadetes?7.2%?;the dominant archaea were Crenarchaeota?94.5%?and the genus Euryarchaeota?5.5%?;and the dominant fungi were Ascomycota?Ascomycota,69.1%?,Basidiomycota?17.6%?and Zygomycota?4.5%?.?-proteobacteria,Acidobacteria and Bacteroidetes were related abundant in Group 1,while Thermolleophilia and Geobacillus were related abundant in Group 2.Prokaryotic communities of the two groups were well separated;the prokaryotic data were primarily correlated with soil elemental compositions and were secondly correlated with environmental attributes?e.g.,soil pH,total organic carbon,NO₃^-,and vegetation coverage;Pearson test,r=0.59 vs.0.52,both P<0.01?.The relatively high abundance of P,S,Cl,and Br in Group 1?Holocene raised beach site?was likely due to landform uplift.Lithophile-elements?Si,Al,Ca,Sr,Ti,V,and Fe?correlated with prokaryotic communities in Group 2 may have originated from weathering of Tertiary volcanic rock.No significant correlations were found between the fungal community distribution and both the soil elemental composition and environmental attributes in this study;however,Monte Carlo tests revealed that elements Sr and Ti,soil pH,sampling altitude,and moss and lichen species numbers had significant impacts on fungal communities.In summary,the elements and nutrients accumulated during the formation of different landforms influenced the development of soils,plant growth,and microbial communities,and this resulted in small-scale spatially heterogeneous biological distributions.These findings provide new evidence that geological evolutionary processes in the Fildes Region were crucial to its microbial community development,and the results highlight that microbial distribution patterns are the legacies of historical events at this small spatial scale.Therefore the ice-free regions in maritime Antarctica represent suitable research sites for studying the influence of geomorphological features on microbial distributions.Secondly,our research on the distribution and succession of soil microbial communities of two different terraces in the Fildes region showed that the structures of microbial communities were distinct,as result from the different geological backgrounds of the two terraces.The terrace of Aldley Island belongs to the coastal uplifting terrace,and each stratum of it has chronological ages.However,the Great Wall Station terrace was formed by various geological factors such as coastal uplift,river?sea?stream erosion and glacial erosion.Through the correlation analysis between soil elements and environmental factors and microbial communities,it was found that Na,Cr,Si,Mg,Al and pH were related to prokaryotic microorganisms in all strata of the Great Wall Station terrace?except E layer?;P,S,Br,TOC,water content and NH₄⁺related to prokaryotic microorganisms in all layer of the Aldley Island?except S0 layer?.The microbial diversity of the Aldley Island terrace was higher,and the prokaryotic microbial changes orderly among the layers.The microbial communities of the Great Wall Station terraces varied greatly among the layers,and the changes did not change orderly according to the height of the layers,which was rather confusing.However,the top and bottom layers of the two terraces showed obvious differences,such as Actinomycetes and Nocardia as maker bacterial group were in the bottom layer of Aldley Island terrace,and Acidobacteria as maker bacterial group was in the top layer;Beijerincklaceae,Crenotrichaceae and Methylococcales as marker bacterial group in the bottom layer of Great Wall Station.In addition,the two terraces had similar succession patterns at the genus level.For example,the abundece of nitrification bacteria Nitrospira and photoautotrophic bacteria Rhodoplanes increase and then decreases along with the increase of the nutritional level.The results showed that compared with the terraces of the Great Wall Station,the time series and microbial community changes of the Aldley Island are relatively clear,so it is more suitable for the futher research on community changes,evolutionary directions and metabolic functions of marine microorganisms to terrestrial microorganisms.Finally,culturable bacterial diversity in the soil of the front edge of the Collins icecap in the Antarctic was studied,it was found that the genus Polaromonas,Psychrobacter and Flavobacterium were the dominant genus in the forefront soil of the icecap as soil exposure.As time increases,Pseudomonas and Arthrobacter gradually become dominant bacteria.Moreover,two potential novel taxa were identified from the 171 isolated strains,and polyphase taxonomic studies were carried out to determine their phylogenetic status,and their strains were named according to their isolation.They were identified as two new bacterial species:Flavobacterium collinsense 4-T-2^T?=CCTCC AB 2014004^T=LMG 28257^T?and Pseudorhodobacter collinsensis 4-T-34^T?=CCTCC AB 2014005^T=LMG28256^T?.In addition,an Arthrobacter sp.24S4-2 with capacitiy of reducing nitrate in a small amount was screened from the foreland of the Collins icecap.The ANI values of the whole genome sequence among strain 24S4-2and other similar strains were all lower than 95%,and the highest GGDC value was only the 24%,speculated to be a novel Arthrobacter species.The strain was able to carry out nitrate reduction at 4°C,a small nitrate concentration?30?M?,and confirmed that hypoxia is a key factor in the initiation of nitrate reduction and further denitrification.At the same time,we found that the strain could concentrate NO₃^-from the medium,and its intracellular NO₃^-concentration could be 4,000-30,000times higher than extracellar NO₃^-concentration,in the meanwhile,strain were forming multi-layered capsule structure in the cell.Transcriptome analysis showed that when the strain accumulates NO₃^-under the condition of carbon source or no carbon source,the genes of ABC transport system and MFS transport system have more transcription than the control groups.The characteristics of high concentration of NO₃^-are closely related to the transmembrane transport system on the cell membrane.In summary,this study open a new thought about the distribution and succession of microbial communities in the extreme environment of the Antarctic,established the foundation for the ecological monitoring of Antarctic microbes,and obtaining new microbial strains with potential applications and research value.It has enriched the polar microbial resource and provided new materials for studying the ecological functions and environmental responses of Antarctic microorganisms.