Roles of salt-tolerant Halobacillus sp. YJT-1 and Bacillus sp. TX-1 in efficient benzo[a]pyrene removal from contaminated water and saline soils.

Benzo[a]pyrene (BaP) contamination in high-salinity environments has received increasing attention; however, few efficient, salt-tolerant microorganisms that can degrade BaP in contaminated soil have been explored. Here, we isolated two salt-tolerant Mn(II)-oxidizing bacteria, Halobacillus sp. YJT-1 and Bacillus sp. TX-1, and evaluated their performance in removing BaP and the relevant underlying mechanisms in saline soils. Extracellular superoxide (O2•-) was identified as a major reactive oxygen species involved in Mn(II) oxidation by both strains, as supported by reactive oxygen species quenching experiments and extracellular O2•- measurements. During in situ biogenic Mn oxide (BMO) formation, the generated extracellular O2•- and BMOs jointly promoted BaP hydroxylation, aromatic ring cleavage, and further transformation to low molecular weight organic matter. Inoculation with YJT-1 and TX-1 significantly increased BaP removal from three saline soils within 14 d, with strain YJT-1 exhibiting significantly greater removal efficiency (51.04-59.62%) than strain TX-1 (43.30-53.84%) (p < 0.05). BaP removal in soils was significantly positively correlated with the presence of amorphous Mn oxides, and laccase activity. Quantitative polymerase chain reaction and metagenomic analyses revealed that inoculation with strains YJT-1 and TX-1 increased the total bacterial abundance, the relative abundance of the polycyclic aromatic hydrocarbon-degradation-related phe gene and the enrichment of pathways associated with biogenic Mn(II) oxidation and the Na+ stress response. These findings provide a microbial strategy for the bioremediation of BaP in high-salinity environments.