Bacillus sp. S361 isolated from bioaerosols in pharmaceutical wastewater treatment plants aggravates Klebsiella pneumoniae-induced lung injury in rats by modulating the gut microbiota.

Current research on bioaerosol diversity in pharmaceutical wastewater treatment plants (PWWTPs) remains limited, especially concerning pulmonary injury mechanisms. Bacterial diversity in two PWWTPs was investigated via high-throughput sequencing and culture-based isolation, revealing functional interactions with pathogenic Klebsiella pneumoniae (Kpn). Emissions showed bimodal size distributions: Plant A dominated by ≥ 7μm particles, Plant B by 0.65-1.1μm submicron fractions enriched with Pseudomonadota (formerly Proteobacteria). Strain S361 (Bacillus sp., Bacillota) isolated from AeT1 exhibited significant synergistic pathogenicity with Kpn. Whole-genome sequencing identified 51 antibiotic resistance genes (ARGs) across 12 resistance mechanisms and 86 virulence factors in Bacillus sp. S361. Mechanistically, Bacillus sp. S361 synergistically enhances pulmonary colonization and pathogenicity of Kpn via distinctive metabolic crosstalk. Co-exposure to S361 and Kpn disrupts gut microbiota homeostasis, inducing dysregulated short-chain fatty acid (SCFA) metabolism and intestinal barrier impairment. This gut-derived dysfunction mediates systemic inflammation through the gut-lung axis, ultimately amplifying Kpn-induced lung injury. Fecal microbiota transplantation (FMT) experiments confirmed gut microbiota's mediating role, as recipient rats developed pathological changes (alveolar septal thickening, inflammatory infiltration) mirroring co-infected groups. Notably, microbiota-depleted rats suffered more severe lung injury than protected counterparts, establishing gut dysbiosis as a critical determinant of pulmonary damage. These findings implicate PWWTP bioaerosols in driving Kpn pathogenicity via Bacillus sp. S361-mediated synergy and gut-lung dysregulation, necessitating targeted interventions for occupational risk mitigation.