Coexistence of diverse metabolic pathways promotes p-cresol biodegradation by Bacillus subtilis ZW

The aromatic compound p-cresol is a notorious industrial pollutant characterized by its high toxicity, persistence and bioaccumulation within higher organisms. A thorough understanding of the microbial metabolic pathways involved in p-cresol degradation is critical for the design and optimization of microbial wastewater treatment systems. Despite numerous studies on the degradation pathways of p-cresol by various microbial species, the metabolic diversity within a single strain remains largely unexplored. This study investigated the metabolic mechanism of p-cresol in Bacillus subtilis ZW, a bacterium capable of degrading p-cresol. Through LC-MS analysis, we identified twelve distinct metabolic intermediates in the culture of strain ZW, leading to the proposal of three plausible degradation pathways. These include methyl hydroxylation, direct aromatic ring hydroxylation, and phosphorylation of the hydroxyl group, and all of which may concurrently contribute to p-cresol biodegradation by strain ZW. Further study showed that the genome of strain ZW harbored 47 coding genes associated with the degradation of p-cresol and its structural analogs, underscoring the metabolic versatility of this strain and its potential for xenobiotic biodegradation. These findings contribute valuable insights into the biodegradation mechanisms of pollutants. Under optimal degradation conditions of 35 °C and pH 7.0, strain ZW demonstrated the capacity to metabolize 27.5 % of p-cresol (10 mg/L) in minimal salt media within a week, and was capable of completely degrading 10 mg/L p-cresol in wastewater within five days. The potential utility of strain ZW in the bioremediation of p-cresol and other aromatic compounds is thus evident.