Study On Diverse Microbial Communities At Ji'nan City And Mt.Tai,Shandong,China

Bioaersol,including the bacteria,fungi,viruses,pollen,animal and plant broken split body,and dust mites,can be adsorbed to the surface of particulate matter and get into the human body through the respiratory tract,enteron and skin.These microbes also provide a medium for the spread of diseases through potential pathogens and allergens.There are also increasing evidence indicating that bacteria can act as cloud condensation nuclei,absorbing or reflecting sunlight,or even participating in N-cycling and C-cycling in the ecosystem.Airborne bacteria have gained growing attentions from scholars,mainly focusing on their potential roles in atmospheric chemistry,nucleation process,and health effects.In the view of air pollution,the ambient bacterial characteristics obtained under polluted air conditions have not been fully studied.In order to better understand the concentration,community distribution,sources,potential function,long-range transport of bioaerosols,we conducted several intensive field at Jinan city and Mt.Tai,China.The results were as follows:The high bacterial concentration in PM0.32-0.56?7314 cells m-3?,PM0.18-0.32?7212 cells m-3?,and PM0.56-1?6982 cells m-3?showed significant negative correlationswith SO2,NO2,and O3.Under sufficient sequencing depth,37 phyla,71 classes,137 orders,236 families,and 378 genera were classified,and the bacterial community structure varied significantly in different size fractions.For example,Holophagaceae?Acidobacteria?in PM0.32-0.56 showed 6-fold higher abundance than that in PM0.18-0.32.Moreover,functional categories and bacterial species?Lactococcus piscium,Pseudomonas fragi,Streptococcus agalactiae and Pseudomonas cichorii?that may potentially be responsible for infections and allergies were also discovered.Source track analysis showed that the ambient bacteria mainly originated fromsoils,leaf surfaces,and feces.Our results highlighted the importance of airborne microbial communities by understanding the concentration,structure,ecological and health effects,especially those in submicron particles during haze episodes.Diverse bacterial population were identified and the majority of bacteria in cloud water were Gram-negative bacteria including Proteobacteria?81.6%?and Bacteroidetes?3.9%?,followed by Gram-positive bacteria Firmicutes?7.1%?andActinobacteria?2.3%?.These Gram-negative taxa mainly inhabited in leaf-surface and cold environments.Meanwhile bacteria involved in the cloud condensation nuclei and ice nuclei formation were observed such as Sphingomonas?6.7%?,Pseudomonas?4.1%?,and Bacillus?1.1%?.In addition,Sphingmonas was more active than that in daytime and participated in the cloud chemistry process.Meanwhile O3 and SO2 critically contributed to the variation of bacterial community.It is the first report on the bacterial community structure of cloud water over Asian area.Our results can serve as an important reference for environmental scientists,and biologists.The bacterial concentration of PM_2.5 obtained at Mt.Tai was 490 cells m-3.The value were much lower than that in other high-altitude sites and near-surface sites.Influenced by the long-range transported northwesterly air mass?42%?,the PM_2.5 showed lower mass concentration and bacterial concentration,but higher diversity indices.The air mass from western mainland of China?33%?induced the highest bacterial concentration and lower bacterial diversity indices of PM_2.5.While influenced by the southeasterly air mass from Yellow Sea?25%?,the bacterial concentration and diversity indices of PM_2.5 were lowest.Most of the bacterial sequences were Gram-negative bacteria such as Burkholderia?33.5%?,Delftia?3.1%?,Bradyrhizobium?2.3%?,and Methylobacterium?2.3%?.The bacterial community presented significant different distribution under the influence of different air-mass trajectories.The long-range transported northwesterly air mass may bring the dust-borne bacteria such as Brevibacillus and Staphylococcus.The southeasterly air mass may induce the increase of Pandoraea and Phylobacterium,while the westerly air mass trajectories may bring more potential pathogens.Based on the spearman analysis,the environmental factors(Cl-,SO42-,K+,Ca²⁺,and Mg²⁺)were found to be crucial for the variation of bacterial community.The results indicated that the local transmission and long-range transport may impact on the diffusion of bacterial community in PM_2.5.At Mt.Tai,the fungal abundance values were 9.4×104 and 1.3×105 copies m-3 in PM_2.5 and PM1,respectively.The daily averaged concentrations of fungal OC in PM_2.5 and PM1 were 6.1 and 8.3 ng C m-3,respectively,with the respective contributions to PM being 0.067 and 0.096%,indicating that airborne fungal spores as a minor source of carbonaceous aerosols cannot be ignored.Most of the fungal sequences were from Ascomycota and Basidiomycota,which are known to actively discharge spores into the atmosphere.The top five orders?Pleosporales,Xylariales,Eurotiales,Capnodiales,and Polyporales?and genera?Alternaria and Aspergillus?were commonly observed in suspended aerosol particles(including TSP,PM10,PM_2.5,and PM1).The three most common species from twelve potentially allergy-inducing species were Aspergillus flavus,Blumeria graminis and Saccharomyces cerevisiae.The fungal community showed a significant seasonal shift across different size fractions based on the Metastats analysis and the Kruskal-Wallis rank sum test.The abundance of Glomerella and Zasmidium increased in larger particles in autumn,whereas Penicillium,Bullera,and Phaeosphaeria increased in smaller particles in winter.Environmental factors,namely,Ca²⁺,humidity,and temperature,were found to be crucial for the seasonal variation in the fungal community.This study might serve as an important reference for fungal contribution to primary biological aerosol particles.