Negative transcriptional control of biotin metabolism genes by the TetR-type regulator BioQ in biotin-auxotrophic Corynebacterium glutamicum ATCC 13032

Genomic context analysis in actinobacteria revealed that biotin biosynthesis and transport (bio) genes are co-localized in several genomes with a gene encoding a transcription regulator of the TetR protein family, now named BioQ. Comparative analysis of the upstream regions of bio genes identified the common 13-bp palindromic motif TGAAC-N3-GTTAC as candidate BioQ-binding site. To verify the role of BioQ in controlling the transcription of bio genes, a deletion in the bioQ coding region (cg2309) was constructed in Corynebacterium glutamicum ATCC 13032, resulting in the mutant strain C. glutamicum IB2309. Comparative whole-genome DNA microarray hybridizations and subsequent expression analyses by real-time reverse transcriptase PCR revealed enhanced transcript levels of all bio genes in C. glutamicum IB2309, when compared with the wild-type strain ATCC 13032. Accordingly, the BioQ protein of C. glutamicum acts as a repressor of ten genes that are organized in four transcription units: bioA-bioD, cg2884-cg2883, bioB-cg0096-cg0097, and bioY-bioM-bioN. DNA band shift assays with an intein-tagged BioQ protein demonstrated the specific binding of the purified protein to DNA fragments containing the candidate BioQ-binding sites, which were located within the mapped promoter regions of bioA, cg2884, bioB, and bioY. These data confirmed the direct regulatory role of BioQ in the control of biotin biosynthesis and transport genes in C. glutamicum. Differential expression of bio genes in C. glutamicum IB2309 was moreover complemented by bioQ genes cloned from other corynebacterial genomes.