The degradation of nicotinic acid is controlled by MarR-family transcriptional regulator NicR in Alcaligenes faecalis

Abstract

Nicotinic acid (NA), or vitamin B3, is a natural pyridine carboxylic derivative, a precursor for numerous essential biological molecules. Previous studies have demonstrated that microorganisms are essential in NA degradation, exhibiting high genetic and metabolic diversity. This study investigated the biodegradation and regulatory properties of NA by the Alcaligenes faecalis JQ135 and the diversity and interrelationships of microbial metabolism of NA. NicR functions as a repressor in the nic cluster. An electrophoretic mobility shift assay (EMSA) demonstrated that NicR can bind to the promoter regions of R, C, B, A, and P operons in strain JQ135, with these multiple binding sites exhibiting the consensus sequence 5′-GTNNAC-3'. Bioinformatics analysis revealed 24 distinct nic cluster order types. The nic gene cluster in strain JQ135 comprises 15 genes arranged in two distantly located fragments and transcribed as five operons. These configurations are conserved within the genus Alcaligenes and are unique compared to the other 23 order types. The functional correlation among NicRs with differing degrees of similarity was examined, revealing that amino acid residues Q64 and V103 are crucial for NicR regulation. This study offers new molecular insights into the various regulatory mechanisms of bacterial degradation of NA in nature.