| Summary: | Fine particulate matter (PM<sub>2.5</sub>) can carry numerous substances and penetrate deep into the respiratory tract due to its small particle size; associated harmful microorganisms are suspected to increase health risks for humans and animals. To find out the microbial compositions of PM<sub>2.5</sub> in piggeries, their interaction and traceability, we collected PM<sub>2.5</sub> samples from a piggery while continuously monitoring the environmental indicators. We also identified pathogenic bacteria and allergens in the samples using high-throughput sequencing technology. We analyzed the microbial differences of PM<sub>2.5</sub> samples at different heights and during different times of day and investigated the microbial dynamics among the PM<sub>2.5</sub> samples. To better understand the interaction between microorganisms and environmental factors among different microbial communities, we applied the network analysis method to identify the correlation among various variables. Finally, SourceTracker, a commonly used microbial traceability tool, was used to predict the source of airborne microorganisms in the pig house. We identified 14 potential pathogenic bacteria and 5 allergens from PM<sub>2.5</sub> in the pig houses, of which <i>Acinetobacter</i> was the dominant bacterium in all samples (relative abundance > 1%), which warrants attention. We found that bacteria and fungi directly affected the the microbial community. The bacterial community mainly played a positive role in the microbial community. Environmental variables mainly indirectly and positively affected microbial abundance. In the SourceTracker analysis using fecal matter and feed as sources and PM<sub>2.5</sub> sample as sink, we found that fecal matter made the greatest contribution to both bacterial and fungal components of PM<sub>2.5</sub>. Our findings provide important insights into the potential risks of pathogens in PM<sub>2.5</sub> to human and animal health and their main sources.
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