Characterization of transcriptional regulator PicR of picolinic acid-degrading bacterium Bordetella petrii strain MY10

Picolinic acid (PA) is a natural carboxylated pyridine derivative with multiple biological sources and applications, which is toxic to both human and animals. PA degradation processes was negatively controlled by MarRfamily regulator PicR. However, the regulatory mechanisms have not been fully investigated and the orphan picR-encoding gene has been rarely reported. In this study, the degradation and regulatory characterizations of PA by a soil bacterium Bordetella petrii strain MY10, were investigated. The pic cluster of strain MY10 consisted of four individual transcriptional units (picR, picCGEDF, picB1B2B3B4 and picA1A2A3) and the picRMY10 gene was separated from the other three transcriptional units. The lag phase of PA degradation was shortened by deleting picRMY10 gene. Electrophoretic Mobility Shift Assay (EMSA) results illustrated that PicRMY10 bound to the promoter regions of transcriptional units of picA, picB, picC and picRMY10. Four DNA-binding regions shared a common palindromic structure: TCAG-N4-CTNN. Three key amino acid residues R19, Q22, V73 of PicRMY10 were studied by site-directed mutagenesis and played crucial roles in PicRMY10 regulation. Bioinformatics analysis of the pic cluster of strain MY10 and 19 related bacteria showed that the PicR proteins were taxon-related and coevolved with its host. This study provides new insights on understandings of the biodiversity of regulatory mechanisms of PA biodegradation by bacteria in nature.