McbG, a LysR Family Transcriptional Regulator, Activates the Gene Cluster Involved in the Upstream Pathway of Carbaryl Degradation in sp. Strain XWY-1.

Although enzyme-encoding genes involved in the degradation of carbaryl have been reported in sp. strain XWY-1, no regulator has been identified yet. In the cluster responsible for the upstream pathway of carbaryl degradation (from carbaryl to salicylate), the gene is constitutively expressed, while is induced by 1-naphthol, the hydrolysis product of carbaryl by McbA. In this study, we identified McbG, a transcriptional activator of the cluster. McbG is a 315-amino-acid protein with a molecular mass of 35.7 kDa. It belongs to the LysR family of transcriptional regulators and shows 28.48% identity to the pentachlorophenol (PCP) degradation transcriptional activation protein PcpR from ATCC 39723. Gene disruption and complementation studies reveal that is essential for transcription of the cluster in response to 1-naphthol in strain XWY-1. The results of the electrophoretic mobility shift assay (EMSA) and DNase I footprinting show that McbG binds to the 25-bp motif in the promoter area. The palindromic sequence TATCGATA within the motif is essential for McbG binding. The binding site is located between the -10 box and the transcription start site. In addition, McbG can repress its own transcription. The EMSA results show that a 25-bp motif in the promoter area plays an important role in McbG binding to the promoter of This study reveals the regulatory mechanism for the upstream pathway of carbaryl degradation in strain XWY-1. The identification of McbG increases the variety of regulatory models within the LysR family of transcriptional regulators. sp. strain XWY-1 is a carbaryl-degrading strain that utilizes carbaryl as the sole carbon and energy source for growth. The functional genes involved in the degradation of carbaryl have already been reported. However, the regulatory mechanism has not been investigated yet. Previous studies demonstrated that the gene, responsible for hydrolysis of carbaryl to 1-naphthol, is constitutively expressed in strain XWY-1. In this study, we identified a LysR-type transcriptional regulator, McbG, which activates the gene cluster responsible for the degradation of 1-naphthol to salicylate and represses its own transcription. The DNA binding site of McbG in the promoter area contains a palindromic sequence, which affects the binding of McbG to DNA. These findings enhance our understanding of the mechanism of microbial degradation of carbaryl.