The Community Structure And Function Of Aerobic Anoxygenic Phototrophic Bacteria In Biological Soil Crusts

One major environment problem is desertification,which seriously threatens people's life and production activities.Biological soil crusts(BSCs)are widely distributed in deserts,and plays key function in the initial process of revegetation and control of desertification of desertification ecosystem.Cyanobacteria have been considered as pioneer species for the formation of BSCs,due to they have abilities of fixing carbon and nitrogen,producing extracellular polysaccharide and others to promote the formation and development of BSCs.Aerobic anoxygenic phototrophic bacteria(AAnPB)have similar or identical functional characteristics to cyanobacteria and may contribute to the formation and development of BSCs.However,there arc few research reports on AAnPB in BSCs.In this paper,took the main deserts in cast and west of Inner Mongolia as the research object,using the traditional isolation and cultivation and high-throughput sequencing,and combined with bioinformatics analysis and microcosm simulation experiments,we determnined the abundance,community structure and composition of bacteria and AAnPB in BSCs first of all,,then predicted and verified the effects of AAnPB on the formation and development of BSCs,finally analyzed the AAnPB strain B3 by multi-omices.The main results are as follows:1.Abundance,community structure and diversity of bacteria and AAnPB in BSCs and environmental impact factorsThe bacteria 16S rRNA gene copy number of BSCs contained more than 108 per gram of soil,AAnPB could account for 0.2-0.3%of the total number of bacteria;and the highest proportion of AAnPB obtained by isolated and cultured is up to 12%of the total number of cultured bacteria.Both results of culture-depentdent and high-throughput sequencing showed that the bacteria in BSCs belong to 6 phylums,such as Proteobacteria,the dominant class are Alphaproteobacteria and Actinobacteria,the relative abundances of Methylobacteriaceae and Sphingomonadaceae were basically stable at 3%and 1.5%,and Sphingomonas was main genus of culturable bacteria.The dominant phylum of AAnPB was Proteobacteria,Alpha-and Beta-proteobacteria were the main class,Rhodospirillaceae,Acetobacteraceae,Rosciflexaccac,Sphingomonadanccac and Mcthylobactcriaccac were the main family.and Methylobacterium(24.14%),Blastomonas(10.34%)and Sphingomonas(10.34%))were the dominant genus in the cultural AAnPB.As to the variant sampling time and space and crust types,the structure and diversity of bacteria and AAnPB community in BSCs are different,especially great difference appeared between eastern and western regions.The main difference was found in the relative abundance of the community.2.The influence and function of AAnPB in formation and development of BSCsThe predicted core AAnPB of natural BSCs in desert areas failed into 5 families,Methylobacteriaceae,Acetobacteraceae,Burkholderiaceae,Rhodospirillaceae and Sphingomonadaceae.Selected the representative strains and inoculated naked sand soil,the results demonstrated these microbe could promote the development of BSCs in different degrees.The results of the microcosm simulation experiment designed based on the characteristics of AAnPB can but Cyanobacteria and other algae cannot utilize near-infrared light showed that the thickness formed by near-infrared light in the experimental group,the content of organic matter and the number of microalgae of BSCs were increased by 24.0%,103.7%and 1447.6%over those of the control,respectively.The core AAnPB microbe(methylotrophs in Methylobacteriaceae and Sphingomonas in Sphingomonadaceae)was significantly associated with the increase in the number of other microbial groups and the accumulation of nutrients such as organic matter.These results indicate that AAnPB plays an important role in the formation and development of BSCs,nutrition enhancement(esp.organic matters accumulation)may be a major cause.3.Whole genome of strain B3 and RubisCo enzyme activity analysisThe photosynthetic gene cluster of AAnPB strain B3 was significantly different from other known auto-or hetero-phototrophic bacteria,with complete Calvin carbon fixation pathway,and RubisCo enzyme activity reached 18.8 ?mol/min·g,suggesting that AAnPB could directly participate in the "carbon sink" process in desert ecosystem.In summary,AAnPB has considerable abundance and high diversity in BSCs,and its community structure is affected by geographical factors,climatic factors and soil physical and chemical properties,especially the precipitation and pH.The core AAnPB microbe are belonging to Methylobacteriaceae,Sphingomonadaceae,Burkho lderiaceae,Acetobacteraceae and Rhodospirillaceae,and they can significantly promote the formation and development of BSCs by enhancing the nutrition level of organic matter,available phosphorus and available nitrogen,increasing the abundance and diversity of algae and fungus,and raising the coverage and thickness of BSCs.Strain B3 of core AAnPB microbe has complete photo-energy utilization and carbon fixation system and RubisCo enzyme activity.This study provides an important theoretical significance and practical basis for the diversity and function of AAnPB in BSCs.