Impact of Yellow Dust Event on PM2.5 Microbial Communities during Spring in Ulaanbaatar, Mongolia

The Ulaanbaatar region in Mongolia exhibits a characteristic increase in particulate matter (PM) concentrations during spring, due to yellow dust events. This phenomenon has emerged as a significant air pollution issue across Asia. Among air pollution indicators, PM_2.5 has substantial impacts on human health and plays a crucial role in microbial community structures and ecological interactions. This study investigated the characteristics of PM_2.5 microbial communities during spring, including a yellow dust event, in Ulaanbaatar, Mongolia. The bacterial and fungal metagenomes of PM_2.5 samples collected in Ulaanbaatar over a week from April 6 to April 12, 2022 were analyzed. DNA was extracted from PM_2.5 filters, and bacterial 16S rRNA gene regions were amplified using 515F/806R primers. For fungi, ITS2 gene regions were amplified using ITS3/ITS4 primers. Subsequently, sequence analysis was performed using Illumina MiSeq. The study examined the impact of air pollutants (NO_x, NO) and meteorological factors (relative humidity (RH), temperature) on microbial diversity indices (Chao1, Shannon) and the characteristics of dominant species during the investigation period. Based on the sequencing results, the relative abundance of bacteria and fungi in PM_2.5 at the genus level was assessed, and changes in microbial abundance before and after the yellow dust event were compared using a heatmap. Additionally, Spearman correlation analysis was conducted to explore the relationships between the Top 5 dominant bacterial and fungal species on the yellow dust event day and the air pollutants as well as meteorological factors. The results indicated that the diversity indices of bacterial and fungal communities during spring tended to be higher with increasing concentrations of air pollutants and temperature; however, higher RH was associated with lower diversity indices. Changes in dominant microorganisms throughout the study period were confirmed through heatmap analysis, revealing that the composition of dominant microorganisms altered before and after the yellow dust event. On the yellow dust day, the Top 5 dominant bacterial genera were identified as Nitrososphaera, Arthrobacter, Nocardioides, Sphingomonas, and Chthoniobacter, while the Top 5 dominant fungal genera were Trichosporon, Cladosporium, Ascochyta, Alternaria and Vishniacozyma. On the event day, the dominant bacterial genera exhibited positive correlations with PM₁₀ concentrations and temperature, while showing negative correlations with RH. Most of these genera are typically found in soil environments and are known to survive in arid conditions. In the case of fungi, the Top 5 fungal species on the yellow dust day, except for Trichosporon, also showed negative correlations with RH. This study may serve as fundamental data for future management strategies of PM_2.5 air quality.