Infoscience

Journal article

Influence of nutritional factors on the nature, yield, and composition of exopolysaccharides produced by Gluconacetobacter xylinus I-2281

The influence of substrate compn. on the yield, nature, and compn. of exopolysaccharides (EPS) produced by the food-grade strain G. xylinus I-2281 was investigated during controlled cultivations on mixed substrates contg. acetate and either glucose, sucrose, or fructose. Enzymic activity anal. and acid hydrolysis revealed that 2 EPS, gluconacetan and levan, were produced by G. xylinus. In contrast to other acetic acid strains, no exocellulose formation has been measured. Considerable differences in metabolite yields have been obsd. with regard to the carbohydrate source. It was shown that glucose was inadequate for EPS prodn., since most of this substrate (0.84 C-mol/C-mol) was oxidized into gluconic acid, 2-ketogluconic acid, and 5-ketogluconic acid. In contrast, sucrose and fructose supported a 0.35 C-mol/C-mol gluconacetan yield. In addn., growing G. xylinus on sucrose produced a 0.07 C-mol/C-mol levan yield. The compn. of EPS remained unchanged during the course of the fermns. Levan sucrase activity was found to be mainly membrane assocd. In addn. to levan prodn., an anal. of levan sucrase's activity also explained the formation of glucose oxides during fermn. on sucrose through the release of glucose. The biosynthetic pathway of gluconacetan synthesis has also been explored. Although the activity of key enzymes showed large differences to be a function of the C source, the ratio of their activities remained similar from one C source to another and corresponded to the ratio of precursor needs as deduced from the gluconacetan compn. [on SciFinder (R)]

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