The degradation of marine abundant compatible solute dimethylsulfoniopropionate was controlled by TetR-family transcriptional regulator DdaR in Alcaligenes faecalis

The copious compatible solute dimethylsulfoniopropionate (DMSP) plays significant roles in marine ecosystems. The DMSP degradation pathways in strain Alcaligenes faecalis M3A have been comprehensively studied, in which DMSP was cleaved into dimethyl sulphide (DMS) and acrylate. However, the transcriptional regulatory mechanism of DMSP degradation is not fully elucidated. In this study, the TetR/AcrR family transcriptional regulator DdaR repressing acuI operon in strain M3A was investigated. The transcription start sites and promoters of the acuI and ddaR operons was identified. DdaR bound to both the acuI and ddaR promoter regions in EMSA experiment. Two binding sites of DdaR shared conserved motif 5′-CNNCGTNACGNNG-3′ which was essential for the DdaR binding. DdaR was inhibited from binding to the acuI promoter region by acrylate, which acted as a ligand of DdaR. Site-directed mutagenesis was used to investigate the impact of four key amino acid residues (Y61, K67, E135, and I169) in DdaR, revealing their essential roles in the functioning of DdaR. The findings of this study unveil a negative transcriptional regulation mechanism of DMSP degradation in A. faecalis M3A by DdaR and provide a new understanding of the TetR/AcrR-type transcriptional regulators.