Community Structure Characteristics And Ecological Function Analysis Of Atmospheric Microbial Aerosols In Typical Cities Of Fenwei Basin

Microbial aerosol existing in airborne fine particulate matter(PM_2.5)have key implications in biogeochemical cycling and human health.At present,researches of microbial aerosol absorbed on PM_2.5are usually conducted over a short timescale,while the long-term studies such as the seasonal variation characteristics of microbial aerosols are still limited,especially the comparisons between different cities in Fenwei Basin.In this study,typical cities of Xi’an（a mega city）and Linfen（a medium city）in Fenwei Basin were taken as the research areas,and atmospheric PM_2.5samples were collected during four seasons.The community compositions of microbial aerosols in atmospheric PM_2.5were detected by the high-throughput sequencing（16S r RNA and 18S r RNA）.Environmental influences on atmospheric microbial aerosols and PM_2.5samples were analyzed.Bacterial aerosol functions were further predicted by Tax4Fun2 and Functional annotation of prokaryotic taxa（FAPROTAX）,and fungal aerosol functions were predicted by FUNGuild.These results were conducted to enhance our understanding of the seasonal changes of community structures and ecological functions in airborne microbial aerosol,and to provide scientific theoretical basis for the prevention and control of atmospheric particulate matter pollution in typical cities in Fenwei Basin.The main results are as follows:（1）The results of Alpha diversity analysis of microbial aerosols in PM_2.5in Xi’an and Linfen showed that the highest richness and diversity of bacterial aerosol were identified in autumn,and that of fungi were found in summer（the diversity of Xi’an exception）.The compositions of microbial aerosols in Xi’an and Linfen were relatively stable at the phylum level across seasons.The bacterial phyla were dominated by Proteobacteria,Actinobacteria,Firmicutes,and Bacteroidetes.Basidiomycota and Ascomycota mainly constituted the fungal phyla.The dominant bacteria at class level were composed of Bacteroidia,Clostridia and Bacilli,while for fungi were Agaricomycetes and Dothideomycetes.However,the seasonal dynamic variations of microbial aerosols compositions and relative abundances were presented at the genus level,and the dominant genera were different in each season.The most abundant bacterial genus in winter,spring,summer,and autumn were Halomonas,Prevotella＿9,Prevotella＿9,Acinetobacter in Xi’an,respectively,while Halomonas,Halomonas,Acinetobacter,Sphingomonas in Linfen,respectively.The most abundant fungal genus in winter,spring,summer,and autumn were Rachicladosporium,Rachicladosporium,Trametes,Rachicladosporium in Xi’an,respectively,while Rachicladosporium,Auricularia,Sporobolomyces,Rachicladosporium in Linfen,respectively.（2）The bacterial aerosols community structure of Xi’an and Linfen was similar in the same season,and the similar seasonal distribution of the bacterial aerosols community structures was found in spring,summer,and autumn.The significant differences were observed in winter likely arose from serious pollution.Both seasonal and regional similarities of fungal aerosols community were found in summer,autumn,and winter of Xi’an and Linfen,but regional differences existed in spring.（3）Temperature（T）and sulfur dioxide（SO₂）in Xi’an,and T,SO₂,and nitrogen dioxide（NO₂）in Linfen were the key factors affecting microbial aerosol community structures,which were associated with different pollution characteristics in Xi’an and Linfen.Sphingomonas and Acinetobacter of bacterial genus dominated in low SO₂concentration in Xi’an and Linfen.Halorubrum and Rhodococcus of bacterial genus and Rachicladosporium of fungal genus dominated in high SO₂concentration in Linfen.（4）Ecological function analysis（Tax4Fun2）of bacteria indicated that metabolism was the most abundant pathway in Xi’an and Linfen,with the highest relative abundance found in autumn.Massilia,Micrococcus,Clostridium＿sensu＿stricto＿1,Corynebacterium＿1,and Bacillus showed a positive correlation with most metabolism-related pathways,especially the microbial growth pathways.Most functional bacteria and disease-related pathways（immune diseases and substance dependence）were positive,and particularly pathogenic bacteria（Pseudomonas,Acinetobacter,Serratia,and Delftia）were positively correlated with most disease-related pathways.The highest relative abundance of Rhodococcus and S cycling was found in the winter of Linfen,which responded to the serious SO₂pollution in Linfen.（5）Fungal function prediction analysis（FUNGuild）showed that the fungal aerosols in PM_2.5in different seasons in Xi’an and Linfen were classified into seven types according to the nutritional mode.The main type was Saprotroph in winter,and the proportion of Pathotroph-Saprotroph-Symbiotroph fungal aerosols was the highest in spring,summer and autumn（summer in Xi’an exception）.The pathogenic and functional fungal aerosols in PM_2.5accumulated in winter,and Talaromyces was the most abundant pathogenic fungus with the highest relative abundance in winter,indicating that atmospheric PM_2.5in winter may have potential exposure risks to human health and ecological environment.