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

Abstract

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-phosphate 4-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.