Regulation of expression of genes involved in quinate and shikimate utilization in Corynebacterium glutamicum

The utilization of the hydroaromatic compounds quinate and shikimate by Corynebacterium glutamicum was investigated. C. glutamicum grew well with either quinate or shikimate as the sole carbon source. The disruption of qsuD, encoding quinate/shikimate dehydrogenase, completely suppressed growth with either substrate but did not affect growth with glucose, indicating that the enzyme encoded by qsuD catalyzes the first step of the catabolism of quinate/shikimate but is not involved in the shikimate pathway required for the biosynthesis of various aromatic compounds. On the chromosome of C. glutamicum, the qsuD gene is located in a gene cluster also containing qsuA, qsuB, and qsuC genes, which are probably involved in the quinate/shikimate utilization pathway to form protocatechuate. Reverse transcriptase PCR analyses revealed that the expression of the qsuABCD genes was markedly induced during growth with either quinate or shikimate relative to expression during growth with glucose. The induction level by shikimate was significantly decreased by the disruption of qsuR, which is located immediately upstream of qsuA in the opposite direction and encodes a LysR-type transcriptional regulator, suggesting that QsuR acts as an activator of the qsuABCD genes. The high level of induction of qsuABCD genes by shikimate was still observed in the presence of glucose, and simultaneous consumption of glucose and shikimate during growth was observed.