Feedback of airborne bacterial consortia to haze pollution with different PM_2.5 levels in typical mountainous terrain of Jinan, China

Polluted air is as harmful as polluted water sources to public health. As air living organisms, the research on microbial consortia under haze stress with different PM_2.5 levels in a mountainous environment remains very limited. This study investigated the dynamic changes in bacterial cell counts, apoptosis, human pathogens, consortia characteristics, metabolic pathways, and the biochemical functions under haze conditions with various degrees of pollution (leading pollutant PM_2.5) from August to December 2017 in a typical mountainous terrain of Jinan, China. Samples were evaluated with flow cytometry and 16S rRNA gene amplicon sequencing. Results indicated that cell counts ranged from 6.83 × 10⁵ ± 1.27 × 10⁴ (non-polluted air, NP) to 2.32 × 10⁶ ± 3.56 × 10⁴ (heavily polluted air, HP) cell m^-3 air. The proportion of viable apoptotic and necrotic cells were positively correlated to PM_2.5. Burkholderia cenocepacia (36.6%) was the most abundant human pathogen found in HP; this gram-negative bacterium is associated with potentially lethal respiratory infections in cystic fibrosis patients. The relative abundance of the phylum Proteobacteria (63.8%) in NP first decreased in lightly polluted (LP) (41.3%) and moderately polluted air (MP) (26.3%) then increased in HP (81.0%). Cupriavidus (22.9%) and BTEX-degrading bacteria (0.6%, Pseudomonas) were found in HP. Metabolic pathways with significant differences included cell motility and endocrine and immune diseases that exhibited increasing relative abundance as pollution levels increased. The diversity of biochemical functions was found to be decreased in hazy air.