Enhanced conversion of soluble starch to trehalose by a mutant of Saccharomycopsis fibuligera sdu.

In our previous studies, it was found that Saccharomycopsis fibuligera sdu cells could accumulate 18.0% (gg(-1)) trehalose from soluble starch in SSY medium. However, the yeast strain contained high activities of acid and neutral trehalases, which were reported to mobilize trehalose accumulated by the cells during fermentation. In order to enhance the yield of trehalose, it is necessary to remove the trehalase activities from the cells. By mutagenesis of ethylmethanesulfonate, one mutant that assimilated trehalose very slowly, but grew on other carbon sources as fast as its parent strain, was isolated. In Biostat B2 2-1 fermentation, trehalose accumulation of the mutant was much higher than that of the wild type when grown in YPS medium containing starch. The activities of acid and neutral trehalases of this mutant were much lower than those of the wild type, respectively. We think the reduction of acid and neutral trehalase activities is considered to be responsible for the increased yield of trehalose accumulated by the mutant.

Effect of NaCl on the growth and morphology of Saccharomycopsis fibuligera.

The effect of NaCl on mycelial growth of Saccharomycopsis fibuligera was examined. Cells were able to grow in medium containing 1 M or 2 M NaCl after adaptation to the salt under standing culture conditions. It took more time to adapt to 2 M NaCl than to 1 M NaCl. Hollow-looking regions in the cells increased during incubation for 20 days in medium without salt, but diminished in cells incubated in medium containing either of the two concentrations of NaCl. The mycelial cells incubated in the medium containing salt were slimmer, and bubble shaped, and malformed cells were observed. The extent of the change was greater in 2 M NaCl than that in 1 M NaCl. NaCl protected cells from leaking, and produced malformed cells.

Use of nystatin for random spore selection in the yeast Saccharomycopsis lipolytica.

Nystatin was used to develop a new method to select spores of the yeast Saccharomycopsis lipolytica. At low concentrations nystatin killed preferently growing cells of this yeast. At high concentrations nongrowing cells were affected as well. In contrast, spores were not sensitive to nystatin action. This differential response to the antibiotic suggested its use to select spores from sporulated yeast cultures.

[Effects of cadmium, zinc, lead and mercury on the growth and accumulating ability of Saccharomyces cerevisiae, Saccharomycopsis lipolytica, Candida tropicalis, and Candida utilis]. / Der Einfluss von Cadmium, Zink, Blei und Quecksilber auf das Wachstum und das Akkumulationsvermögen von Saccharomyces cerevisiae, Saccharomycopsis lipolytica, Candida tropicalis und Candida utilis.

The effects of cadmium, zinc, lead, and mercury on the growth and the accumulating ability of Saccharomyces cerevisiae, Saccharomycopsis lipolytica, Candida tropicalis, and Candida utilis had been studied. Generally the experiments resulted in the following findings: Very small concentrations of cadmium and mercury already decrease the growth intensity of the yeasts by lengthening the lag period and the doubling time. The cell yield is not reduced. Zinc increases the productivity of Saccharomyces cerevisiae and Saccharomycopsis lipolytica by shortening the lag period. The lead concentrations investigated show no significant influence on the growth. Low pH values intensify the effectiveness of the four heavy metals. The yeasts tested accumulate heavy metals, especially cadmium, to high concentrations and therefore substrates containing heavy metals are only limited suitable for the scp-production with yeasts.

Cytoplasmic transfer of oligomycin resistance during protoplast fusion of Saccharomycopsis lipolytica.

Mitotic segregation of oligomycin resistance and oligomycin sensitivity was observed among the prototrophic progeny of protoplast fusion between drug-resistant and drug-sensitive complementary auxotrophs of Saccharomycopsis lipolytica. The transfer of oligomycin resistance by protoplast fusion without karyogamy suggests a cytoplasmic inheritance of this drug resistance determinant.

Genetic control of lysine permeases in Saccharomycopsis lipolytica.

In order to obtain strains of Saccharomycopsis lipolytica impaired in the active transport of L-lysine, mutants resistant to a mixture of L-canavanine, L-4-5-transdehydrolysine and L-S-amino ethylcysteine, taken either all three or two by two, were isolated. These compounds were shown previously to be competitive inhibitors of L-lysine uptake. The resistance patterns and excretion capacity of the mutants were established. All mutants behaved as monogenic. Recombination tests indicated that four genes at least were involved. All mutants were impaired in both high and low affinity L-lysine transport systems. Several hypotheses on the functions of these genes are put forward and discussed.

Reversion by Fe(III) of the inhibition by hydroxamic acids of the cyanide-insensitive respiration in the yeast Saccharomycopsis lipolytica.

The specific inhibitory effect of benzhydroxamic acid on the cyanide-insensitive respiration could be reversed in whole cells of the yeast Saccharomycopsis lipolytica, by addition of Fe(III), in a way suggesting a competition between the added iron and an enzyme-bound metallic ion, both central atoms for the ligand benzhydroxamic acid. The possibility that added metal ions modify the penetration of BHAM into the cells was ruled out. Co(II), Cu(II) and Al(III) could substitute for Fe(III). A linear relation between the concentration in added Fe(III) and the reversed respiration rate was observed. At a given cell concentration, the reversion by added Fe(III) of the inhibitory effect of benzhydroxamic acid on the alternative respiration appeared more related to the degree of inhibition rather than to the concentration in added inhibitor. Increasing cell concentrations required increasing amounts of Fe(III) to reach the same level of reversion. No reversal occurred at concentrations in added Fe(III) lower than 0.1 mM, whatever the benzhydroxamic concentration, the cell concentration or the yeast batch.

Methionine overproduction by Saccharomycopsis lipolytica.

Six ethionine-resistant (Etr) regulatory mutants of Saccharomycopsis lipolytica Sl/1 overproducing methionine have been isolated. Five of them are also resistant to seleno-methionine. The activity of homocysteine synthase (O-acetyl-L-hormoserine-acetate lyase, adding hydrogen sulfide) is derepressed in these mutants and is not susceptible to the methionine-mediated repression. The pool of free methionine in Etr mutants is enhanced 1.5 to 18 times, and incorporation of 35S into methionine is 1.5 to 50 times higher than that in the wild strain. Neither accumulation of endogenous free methionine in Etr mutants nor the uptake of exogenous methionine is accompanied by an increase in the S-adenosylmethionine pool. This implies compartmentation of methionine metabolism in S. lipolytica.