Novel insights into seasonal airborne bacterial interactions and potential threats to human health in a northwest city, China

Bioaerosols significantly influence air quality and human health. This study investigated the diversity, structure, and interaction of bacterial communities in particulate matter (PM_2.5) across four seasons in Xi'an. The results revealed that operational taxonomic units (OTUs) were the highest in autumn, reaching levels comparable to those in winter, but were 3.7 and 1.8 times higher than in summer and spring respectively. The Chao1 index was the highest in winter and the lowest in summer. Proteobacteria dominated in summer (38.8%) and spring (35.9%), while Actinobacteria was more abundant in autumn (43.1%) and winter (50.9%). Co-occurrence network analysis showed more complex microbial relationships in spring and summer, with increased bacterial competition observed in summer, evidenced by the highest negative edges ratio (8.7%). Potential pathogenic bacteria were most prevalent in winter (41.1%), compared to 12.1% in spring and 18.6% in summer. Notably, Rhodococcus and Gardnerella were significantly enriched in winter and autumn, while Acinetobacter and Bacteroides were more prevalent in spring and summer, as indicated by STAMP analysis. This study provides crucial insights into how seasonal changes affect bacterial interactions and the potential pathogenicity of airborne bacterial communities, highlighting their potential threats to human health.