Unveiling the regulatory mechanisms of salicylate degradation gene cluster in sp. strain X9.

In a previous study, the novel gene cluster was found to be involved in salicylate degradation through the CoA-mediated pathway in sp. strain X9 (Mol Microbiol 116:783-793, 2021). In this study, an IclR family transcriptional regulator CehR4 was identified. In contrast to other regulators involved in salicylate degradation, forms one operon with the gentisyl-CoA thioesterase gene , while and (encoding salicylyl-CoA ligase and salicylyl-CoA hydroxylase, respectively) form another operon. and are divergently transcribed, and their promoters overlap. The results of the electrophoretic mobility shift assay and DNase I footprinting showed that CehR4 binds to the 42-bp motif between genes and , thus regulating transcription of and . The repeat sequences IR1 (5'-TTTATATAAA-3') and IR2 (5'-AATATAGAAA-3') in the motif are key sites for CehR4 binding. The arrangement of and and the conserved binding motif of CehR4 were also found in other bacterial genera. The results disclose the regulatory mechanism of salicylate degradation through the CoA pathway and expand knowledge about the systems controlled by IclR family transcriptional regulators.IMPORTANCEThe long-term residue of aromatic compounds in the environment has brought great threat to the environment and human health. Microbial degradation plays an important role in the elimination of aromatic compounds in the environment. Salicylate is a common intermediate metabolite in the degradation of various aromatic compounds. Recently, sp. strain X9, capable of degrading the pesticide carbaryl, was isolated from carbaryl-contaminated soil. Salicylate is the intermediate metabolite that appeared during the degradation of carbaryl, and a novel salicylate degradation pathway and the involved gene cluster have been identified. This study identified and characterized the IclR transcription regulator CehR4 that represses transcription of gene cluster. Additionally, the genetic arrangements of and and the binding sites of were also found in other bacterial genera. This study provides insights into the biodegradation of salicylate and provides an application in the bioremediation of aromatic compound-contaminated environments.