A Zymomonas mobilis Mutant with Delayed Growth on High Glucose Concentrations

Abstract

Exponentially growing cells of Zymomonas mobilisnormally exhibit a lag period of up to 3 h when transferred from 0.11 M (2%) to 0.55 M (10%) glucose liquid medium. A mutant ofZ. mobilis (CU1Rif2), fortuitously isolated, showed more than a 20-h lag period when grown under the same conditions, whereas 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 fructose) 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 on 0.55 M glucose on which wild-type cells had been incubated for 3 h and removed at the beginning of their exponential phase. This apparent preconditioning 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 cells. Undelayed growth of CU1Rif2 on 0.55 M glucose previously conditioned by the wild type was impaired by heating or protease treatment. It is suggested that in Z. mobilis, a diffusible proteinaceous heat-labile factor, transitionally not present in 0.55 M glucose CU1Rif2 cultures, triggers growth on 0.55 M glucose. Biochemical analysis of glucose uptake and glycolytic enzymes implied that glucose assimilation was not directly involved in the phenomenon. By use of a wild-type Z. mobilis genomic library, a 4.5-kb DNA fragment which complemented in low copy number the glucose-defective phenotype as well as glucokinase and glucose uptake of CU1Rif2 was isolated. This fragment carries a gene cluster consisting of four putative coding regions, encoding 167, 167, 145, and 220 amino acids with typical Z. mobilis codon usage, −35 and −10 promoter elements, and individual Shine-Dalgarno consensus sites. However, strong homologies were not detected in a BLAST2 (EMBL-Heidelberg) computer search with known protein sequences.

Physiological effects of overexpressed sigma factors on fermentative stress response of Zymomonas mobilis

“…It is tempting to assume that membrane changes and the maintenance of macromolecules are also related to cellular response to high ethanol and glucose concentrations, but so far, the experimental data are based on few works with Z. mobilis in the presence of high concentrations of glucose [24,32] or ethanol [10,20,33,34], and the overlap of these data is not yet conclusive.…”

Use of a green fluorescent protein gene as a reporter in Zymomonas mobilis and Halomonas elongata

“…Zymomonas mobilis is a Gram‐negative anaerobic bacterium with industrial importance that produces ethanol from hexoses at high rates and yields [1]. It has an unusual tolerance for high concentrations of ethanol and glucose [1,2]. Plasmid vectors have been developed for Z. mobilis , mutants can be isolated by various mutagenic treatments, and some Z. mobilis genes have been cloned in heterologous hosts [3].…”

Effect of the Feed Substrate Concentration on the Dynamic Performance of the Bioethanol Fermentation Process Using Zymomonas mobiliz

“…19 Theoretically, bioethanol yields around 1.9 mol of bioethanol/mol of glucose or 0.49 g of bioethanol/g of glucose consumed are obtained. 20 There are many challenges for the production of bioethanol from agricultural residues, such as pretreatment and enzymatic hydrolysis of lignocelluslic biomass to simpler sugars, generation of fermentation inhibitors during pretreatment, and fermentation of mixed sugars, such as hexoses and pentoses, to bioethanol. One of the main disadvantages accompanied by bioethanol fermentation by Z. mobiliz is that, at specific operating conditions, oscillatory behavior of the concentration of substrates, bioethanol, and cells takes place, leading to instability of the fermentation system.…”

“…mobiliz . Theoretically, bioethanol yields around 1.9 mol of bioethanol/mol of glucose or 0.49 g of bioethanol/g of glucose consumed are obtained …”