Carbon,Nitrogen,and Sulfur Metabolisms Potentially Mediated By Airborne Microorganisms And Their Possible Influence On Air Secondary Pollution

Airborne microorganisms are widely distributed in the atmosphere and have a great influence on the ecosystem and human health.Many researchers have paid attention to the structure,influencing factors,potential sources,and health effects of airborne microorganisms.However,most studies focused on the community composition of airborne microorganisms,the microbial function rarely gained attention.Microorganisms metabolize actively in the soil and water environments,so do they possible to carry out functional metabolism in the atmosphere.In this research,airborne microorganism samples were collected in China and Switzerland.High-throughput amplicon sequencing and metagenomics were used to study the microbial function and its potential effect on air pollution.Microcosm experiments and neural network models were used to verify and predict the contribution of microbial metabolism to air pollutants.Main results of this study were listed as below:1.Airborne microorganisms involved in carbon,nitrogen,and sulfur metabolisms.In the atmosphere,45.79%,26.83%,and 6.32% of the total microorganisms have the potential to conduct carbon,nitrogen,and sulfur metabolisms,respectively.Among these genera for carbon,nitrogen,and sulfur metabolisms,the number of keystone taxa was 6,11,and 1,respectively;while the number of core taxa was 10,5,and 2,respectively.Airborne microorganisms that mediated carbon metabolism did not cause a contribution to the formation of organic carbon.However,the microbial nitrogen and sulfur metabolisms may contribute to the formation of ammonium and sulfate.Microbial nitrogen and sulfur metabolisms may have effects on air secondary pollution.2.Functional genes encoding nitrogen and sulfur metabolisms in the atmosphere.In the nitrogen metabolism,airborne microorganisms have the potential to catalyze ammonium formation but not ammonium oxidation since no ammoxidation genes were identified.The concentration of gdh genes encoding ammonification was 6.18×104 copies·m^-3.In the sulfur metabolism,the relative abundance of sulfate-forming genes was 1.56 times that of sulfate-reducing genes.The concentration of sox B genes (4.14×10³ copies·m^-3)encoding thiosulfate oxidation was 1.50 times that of cys DNC genes(2.76×10³ copies·m^-3)encoding sulfate reduction.It indicated that microbial nitrogen and sulfur metabolisms may conduce to the formation of ammonium and sulfate,leading to the accumulation of ammonium and sulfate,respectively.3.Correlations between functional genes for nitrogen and sulfur metabolisms and environmental factors.The concentrations of PM_2.5 and PM₁₀ were positively correlated with the concentrations of total bacteria,gdh genes for ammonification,sox B for thiosulfate oxidation,and cys DNC genes for sulfate reduction?p < 0.05?.Besides,the u-component of wind had positive correlations with the concentration of total bacteria,sox B genes,and cys DNC genes?p < 0.05?.Latitude and altitude had positive relationships with the concentration of cys DNC genes?p < 0.05?.The other environmental factors had no significant correlations with total bacteria and functional genes.Thus,PM_2.5 and PM₁₀ were the most important factors for microbial nitrogen and sulfur metabolisms.4.Calculation of microbial contributions to atmospheric ammonium and sulfate.In the ammonification microcosms,the increasing rate of NH4+ was 0.05 ng per 104 copies of gdh gene.In the thiosulfate oxidation microcosms,the increasing rates of SO₄^2-was 0.04 ng per 104 copies of sox B gene.The microbial ammonification would contribute 0.36 ?g·m^-3 ammonium,which occupied 8.00% of the weight of total ammonium on average.The microbial thiosulfate oxidation would contribute 0.09 ?g·m^-3 sulfate,which occupied 1.71% of the weight of total sulfate on average.Based on correlation analyses of total bacteria,functional genes,and environmental factors,the neural network model revealed that the heavier the air pollution was,the greater the contribution of microbial ammonification to atmospheric ammonium weight would be.