Activity of glucose-fructose oxidoreductase in fresh and permeabilised cells of Zymomonas mobilis grown in different glucose concentrations

Abstract

Previously grown cells of the ethanologenic bacterium Zymomonas mobilis produce sorbitol and gluconic acid, in reactions catalysed by the periplasmic enzymes glucose-fructose oxidoreductase (GFOR) and glucono-δ-lactonase (GL). The GFOR/GL system activity, in cells to be used in this bioconversion, depends on growth conditions. In batch runs, with initial glucose concentrations (S0) from 42 to 230 g/L, the highest specific and total GFOR/GL activities were obtained with S0 = 153 g/L (12.6 U/g cells and 62 U/L). Higher S0 led to decreasing activities in fresh cells. With S0 = 209 g/L, the final specific activity was only 7.0 U/g. After disruption of cells, however, an activity over 15 U/g was revealed. Since growth inhibition with S0 over 153 g/ L was observed in batch mode, fed-batch runs, equivalent to a batch of 230 g/L, were done. Although no growth inhibition occurred in fed-batch cultivation, enzyme activity remained low (5.2 U/g). A further fedbatch experiment, carried out under low pressure to remove ethanol from the medium, resulted in a specific activity of 9.8 U/g and a total activity of 68.7 U/L. These results indicate that the low GFOR/GL activities in Z. mobilis cells grown on higher S0 were due to changes in the cell wall, caused by high concentration of ethanol, that hindered the transport of the substrate to the intracellular enzymes in biconversion runs. This conclusion was confirmed by bioconversion runs with cells cultivated under different conditions.

Analysis of experimental errors in bioprocesses. 1. Production of lactobionic acid and sorbitol using the GFOR (glucose-fructose oxidoreductase) enzyme from permeabilized cells of Zymomonas mobilis

“…This influence had already been reported by Zachariou and Scopes [24]. In that study, the authors showed that the highest activity of GFOR was obtained when a high glucose concentration was added to a However, glucose concentrations [150 g l -1 cause an inhibition of the cellular growth [8].…”

“…Both rich and defined composition media were prepared. Media containing glucose concentrations [150 g l -1 were not used because of the known substrate inhibition at high sugar concentrations [8].…”

Synthesis of sorbitol by Zymomonas mobilis under high osmotic pressure

“…Other uses include vitamin C, sorbose, glycerol propylene, plastics and resin production. Sorbitol can be used in dietetic foods for diabetics because it is not insulindependent (6,17).…”

“…After the catalytic hydrogenation process, the sorbitol is collected and purified, making the process expensive (6,8). However, other methods can be used to obtain sorbitol, such as the biotechnological process by fermentation.…”

Simulated moving bed technology to improve the yield of the biotechnological production of lactobionic acid and sorbitol

“…In these experimental runs, high concentrations of the substrate are used, since it consists of a more favorable condition to the action of the GFOR enzyme (Silveira et al 1999;Erzinger et al 2003). One can verify kinetic curves for the initial concentration of around 0.7 mol L −1 lactose and initial concentrations of around 0.35 mol L −1 Fig.…”