Identification and Functional Analysis of the Gene Cluster for L-Arabinose Utilization in Corynebacterium glutamicum

Corynebacterium glutamicum ATCC 31831 grew on L-arabinose as the sole carbon source at a specific growth rate that was twice that on D-glucose. The gene cluster responsible for L-arabinose utilization comprised a six-cistron transcriptional unit with a total length of 7.8 kb. Three L-arabinose-catabolizing genes, araA (encoding L-arabinose isomerase), araB (L-ribulokinase), and araD (L-ribulose-5-phosphate4-epimerase), comprised the araBDA operon, upstream of which three other genes, araR (LacI-type transcriptional regulator), araE (L-arabinose transporter), and galM ( putative aldose 1-epimerase), were present in the opposite direction. Inactivation of the araA, araB, or araD gene eliminated growth on L-arabinose, and each of the gene products was functionally homologous to its Escherichia coli counterpart. Moreover, compared to the wild-type strain, an araE disruptant exhibited a > 80% decrease in the growth rate at a lower concentration of L-arabinose (3.6 g liter(-1)) but not at a higher concentration of L-arabinose ( 40 g liter(-1)). The expression of the araBDA operon and the araE gene was L-arabinose inducible and negatively regulated by the transcriptional regulator AraR. Disruption of araR eliminated the repression in the absence of L-arabinose. Expression of the regulon was not repressed by D-glucose, and simultaneous utilization of L-arabinose and D-glucose was observed in aerobically growing wild-type and araR deletion mutant cells. The regulatory mechanism of the L-arabinose regulon is, therefore, distinct from the carbon catabolite repression mechanism in other bacteria.