Genomic insights into phenol degradation by halophilic bacteria and their potential application in saline soil remediation

Phenol, a persistent toxicant in industrial effluents, poses a risk to ecosystems and public health. As an environmentally sustainable solution, microbial bioremediation has gained attention. In this study, next-generation whole-genome sequencing was performed on two phenol-degrading halophilic bacteria, PT-11 and PT-20. Strain PT-11 encoded 10 key genes related to phenol degradation, compared to 9 key genes in strain PT-20. Notably, strain PT-11 possessed two genes for catechol 1, 2-dioxygenase, which was involved in the ortho-cleavage pathway. In contrast, strain PT-20 contained two genes for catechol 2, 3-dioxygenase, which was associated with the meta-cleavage pathway. These findings suggested that the complementary metabolism between the two strains might enhance phenol degradation. The mixed strains demonstrated remarkable efficiency in phenol degradation under hypersaline conditions (5% NaCl), achieving complete phenol degradation within 42 h at 800 mg/L, 54 h at 1000 mg/L, and 72 h at 1200 mg/L. Moreover, the mixed strains showed high efficiency in remediation of soil contaminated with 5% NaCl and 300 mg/kg phenol, with rapid reduction in phenol content within 48 h and full degradation by 72 h. Soil microbial diversity analysis showed that the relative abundance of Oceanobacillus peaked at 95.59% at 0 h, slightly dropped to 94% at 24 h, and significantly decreased to 21.15% by 72 h. As phenol content decreased over time, the community composition diversified and gradually resembled that of the blank control group. Overall, these findings demonstrated the potential of these halophilic bacteria for bioremediation of phenol-contaminated environments, particularly in high-salinity conditions.