Insights into the potential pathogenic bacteria and their interactions with meteorology and atmospheric pollution conditions examined during summer and winter in Xi’an, China

Bioaerosols can influence the atmospheric environment and human health. In this study, we investigated the diurnal variations of bioaerosols and the bacterial communities in PM_2.5 during summer and winter. The fungal concentration (795.7 CFU/m³) was higher in winter, and bacteria concentration (315.9 CFU/m³) was higher in summer. For TAMs, summer concentration (19.9 × 10⁶ cell/m³) was 1.4 times higher than that in winter. The bacterial and fungal concentrations were the lowest in the afternoon, along with the highest level of ozone, which damaged microbial DNA and inhibited their growth. The concentration of TAMs exhibited a bimodal distribution with two peaks coinciding with morning and evening traffic rush hours. In winter, the number of bacterial operational taxonomic units was 3 times higher than that in summer. Proteobacteria peaked in the evening (48.5%), and Actinobacteria (18%) appeared at the same time in summer. During summertime, the morning and afternoon genera were different from the evening and night genera, while the composition of bacterial communities was stable in winter. Four potentially pathogenic bacteria (Pseudomonas, Serratia, Bacteroides, and Streptococcus) were detected in summer, but only one (Acinetobacter) was detected in winter. The Mantel test revealed that the abundance of pathogenic bacteria were influenced by the relative humidity, ozone level, and carbon monoxide level in summer, while it was more complicated for the interaction role among high PM_2.5 levels, oxidative potential, as well as meteorological parameters with pathogenic bacteria in winter. This study provides important insights into the effects of bioaerosol pollution that could affect human health.