Production of organic acids by periplasmic enzymes present in free and immobilized cells of Zymomonas mobilis

Abstract

In this work the periplasmic enzymatic complex glucose-fructose oxidoreductase (GFOR)/glucono-δ-lactonase (GL) of permeabilized free or immobilized cells of Zymomonas mobilis was evaluated for the bioconversion of mixtures of fructose and different aldoses into organic acids. For all tested pairs of substrates with permeabilized free-cells, the best enzymatic activities were obtained in reactions with pH around 6.4 and temperatures ranging from 39 to 45 °C. Decreasing enzyme/substrate affinities were observed when fructose was in the mixture with glucose, maltose, galactose, and lactose, in this order. In bioconversion runs with 0.7 mol l(-1) of fructose and with aldose, with permeabilized free-cells of Z. mobilis, maximal concentrations of the respective aldonic acids of 0.64, 0.57, 0.51, and 0.51 mol l(-1) were achieved, with conversion yields of 95, 88, 78, and 78 %, respectively. Due to the important applications of lactobionic acid, the formation of this substance by the enzymatic GFOR/GL complex in Ca-alginate-immobilized cells was assessed. The highest GFOR/GL activities were found at pH 7.0-8.0 and temperatures of 47-50 °C. However, when a 24 h bioconversion run was carried out, it was observed that a combination of pH 6.4 and temperature of 47 °C led to the best results. In this case, despite the fact that Ca-alginate acts as a barrier for the diffusion of substrates and products, maximal lactobionic acid concentration, conversion yields and specific productivity similar to those obtained with permeabilized free-cells were achieved.

AVALIAÇÃO DA TEMPERATURA NA PRODUÇÃO DE ÁCIDO LACTOBIÔNICO E SORBITOL POR CÉLULAS DE Zymomonas mobilis IMOBILIZADAS EM ALGINATO DE CÁLCIO

“…Perfis de diminuição de µ P menos acentuados foram observados com a utilização de temperaturas inferiores a 47°C. Zachariou & Scopes (1986) e Malvessi et al (2013) relataram a temperatura de 39°C como favorável para a conversão de substratos em produtos pelo complexo enzimático GFOR/GL, com a utilização de células livres de Z. mobilis. Como pôde ser observado, em se tratando de um sistema imobilizado, o fluxo da solução de substratos e produtos tem o comportamento afetado pela barreira representada pelo suporte, em elevada concentração celular no interior das esferas.…”

Removal of lactobionic acid by electrodialysis

“…Nevertheless, the greatest commercial application is in the medical field, as the main constituent of fluid for organ preservation during the procedure of transplantation. Lactobionic acid is obtained industrially by dehydrogenation of the lactose using a metallic catalyst (Splechtna et al, 2001;Dhariwal et al, 2006;Paul and Patrick, 2009;Pedruzzi et al, 2011;Severo Júnior et al, 2011;Malvessi et al, 2013).…”

“…Recent studies have shown some alternatives for the production of lactobionic acid, as for example, biotechnological and electrochemical processes, both still in development (Miyamoto et al, 2000;Splechtna et al, 2001;Dhariwal et al, 2006;Severo Júnior et al, 2011;Malvessi et al, 2013). According to Jonas and Silveira (2004), a promising route for production of lactobionic acid is from lactose and fructose by enzymatic catalysis using permeabilized cells of Zymomonas mobilis.…”

Bioproduction and characterization of sodium, potassium, and calcium lactobionates

“…6,7 Some reports show the use of the anaerobic bacterium Zymomonas mobilis to produce lactobionic acid / lactobionate. [10][11][12] This microorganism, presents in its periplasm the glucose-fructose oxidoreductase (GFOR, EC 1.1.99.28)/glucono-lactonase (GL, EC 3.1.1.17) complex. These enzymes operate on a ping-pong mechanism, in which lactose is oxidized to lactobiono-δ-lactone while fructose, which is employed as substrate for the regeneration of the NADPH cofactor, is reduced to sorbitol.…”

“…Subsequently, by the action of GL, lactobiono-δ-lactone is hydrolyzed to lactobionic acid ( Figure 1). 11,13 In the bioproduction of lactobionic acid and sorbitol, using Z. mobilis GFOR/GL system, the pH of the reaction medium should be controlled in order to maintain the catalytic activity of the enzyme. As the lactobionic acid is formed, there is a tendency to decrease the pH and, for the maintenance of the catalytic activity, it should be kept at 6,4.…”