A Zymomonas mobilis mutant with delayed growth on high glucose concentrations

Exponentially growing cells of Zymomonas mobilis normally exhibit a lag per iod of up to 3 h when transferred from 0.11 M (2%) to 0.55 M (10%) glucose liquid medium. A mutant of Z, mobilis (CU1Rif2), fortuitously isolated, sho wed more than a 20-h lag period when grown under the same conditions, where as on 0.55 M glucose solid medium, it failed to grow. The growth of CU1Rif2 on elevated concentrations of other fermentable (0.55 M sucrose or fructos e) or nonfermentable (0.11 M glucose plus 0.44 M maltose or xylose) sugars appeared to be normal, Surprisingly, CU1Rif2 cells grew without any delay o n 0.55 M glucose on which wild-type cells had been incubated for 3 h and re moved at the beginning of their exponential phase. This apparent preconditi oning was not observed with medium obtained from wild-type cells grown on 0 .11 M glucose and supplemented to 0.55 M after removal of the wild-type cel ls. Undelayed growth of CU1Rif2 on 0.55 M glucose previously conditioned by the wild type was impaired by heating or protease treatment. It is suggest ed that in Z, mobilis, a diffusible proteinaceous heat-labile factor, trans itionally not present in 0.55 M glucose CU1Rif2 cultures, triggers growth o n 0.55 M glucose. Biochemical analysis of glucose uptake and glycolytic enz ymes implied that glucose assimilation was not directly involved in the phe nomenon. By use of a wild-type Z. mobilis genomic library, a 4.5-kb DNA fra gment which complemented in low copy number the glucose-defective phenotype as well as glucokinase and glucose uptake of CU1Rif2 was isolated. This fr agment carries a gene cluster consisting of Four putative coding regions, e ncoding 167, 167, 145, and 220 amino acids with typical Z, mobilis codon us age, -35 and -10 promoter elements, and individual Shine-Dalgarno consensus sites. However, strong homologies were not deterred in a BLAST2 (EMBL-Heid elberg) computer search with known protein sequences.