Cloning and molecular analysis of a mannitol operon of phosphoenolpyruvate-dependent phosphotransferase (PTS) type from Vibrio cholerae O395

A putative mannitol operon of the phosphoenolpyruvate phosphotransferase (PTS) type was cloned from Vibrio cholerae 0395, and its activity was studied in Escherichia coli. The 3.9-kb operon comprising three genes is organized as mtIADR. Based on the sequence analysis, these were identified as genes encoding a putative mannitol-specific enzyme IICBA (EIIMd) component (MtIA), a mannitol-1-phosphate dehydrogenase (MtID), and a mannitol operon repressor (MtIR). The transport of [H-3]mannitol by the cloned mannitol operon in E. coli was 13.8 +/- 1.4 nmol/min/mg protein. The insertional inactivation of EIIMd abolished mannitol and sorbitol transport in V. cholerae O395. Comparison of the mannitol utilization apparatus of V. cholerae with those of Gram-negative and Gram-positive bacteria suggests highly conserved nature of the system. MtIA and MtID exhibit 75% similarity with corresponding sequences of E. coli mannitol operon genes, while MtIR has 63% similarity with NUR of E. coli. The cloning of V. cholerae mannitol utilization system in an E. coli background will help in elucidating the functional properties of this operon.