Fuels and industrial chemicals through biotechnology. 2

Kinetics of ethanolic fermentation of D-xylose by Klebsiella pneumoniae and its mutants

The microbial production of ethanol from D-xylose by a new soil isolate of Klebsiella pneumoniae and the mutants K. pneumoniae MB-16 and MB-16-1048 was studied. Kinetic and physiological properties of the mutants were compared with those of the original isolate. The volumetric rates of ethanol formation by mutants MB-16-1048 and MB-16 and the original isolate were 1.58, 0.50, and 0.06 g liter-1 h-1, respectively. The cultivation times of mutants MB-16-1048 and MB-16 were 20 and 18 h, respectively, and that of the original isolate was 118 h. Both the mutants exhibited metabolic similarities with the original isolate. Ethanol was the major end product of fermentation in all three strains. Acetic acid and carbon dioxide were the other two important by-products of fermentation. Pyruvic acid was accumulated in significant proportions as an intermediate. The proportion of pyruvate in the original isolate was 54% of the total D-xylose utilized, whereas for MB-16 and MB-16-1048 the values were about 42 and 22%, respectively. The lower fractions of pyruvate in mutants MB-16 and MB-16-1048 showed up as a 41 and 82% improvement, respectively, over the original isolate in terms of the ethanol yield.

Nonconventional yeasts: their genetics and biotechnological applications

To date, more than 500 species of yeasts have been described. Most of the genetic and biochemical studies have, however, been carried out with Saccharomyces cerevisiae. Although a considerable amount of knowledge has been accumulated on fundamental processes and biotechnological applications of this industrially important yeast, the large variety of other yeast genera and species may offer various advantages for experimental study as well as for product formation in biotechnology. The genetic investigation of these so-called unconventional yeasts is poorly developed and information about corresponding data is dispersed. It is the aim of this review to summarize and discuss the main results of genetic studies and biotechnological applications of unconventional yeasts and to serve as a guide for scientists who wish to enter this field or are interested in only some aspects of these yeasts.