[Selection and properties of mutant yeast Pichia guilliermondii strains resistant to chromium (VI)].

Yeast Pichia guilliermondii strains L3 and L2, exposed to UV mutagenesis, produced over 80 mutants capable of growing on media containing 1.5 mM bichromate (Cr(VI)). The mutations making the strains resistant to Cr(VI) were dominant or semidominant.

[Riboflavin transport in mutant of Pichia guilliermondii yeast with damaged glucose uptake].

The mutant of P. guilliermondii yeast MS-50 which had lost the ability to grow in a glucose-containing medium but not in the presence of sucrose or maltose was selected. The mutant has a damaged glucose uptake from the medium.

[Overproduction of riboflavin in mutants of Pichia guilliermondii yeasts resistant to 7-methyl-8-trifluoromethyl-10-(1'-D-ribityl)isoalloxazine].

Mutants resistant to 7-methyl-8-trifluoromethyl-10-(1'-D-ribityl)isoalloxazine were selected from the yeast Pichia guilliermondii, strain MS14-A10, possessing a multiple sensitivity to antibiotics and antimetabolites. A lot of such mutants displayed an elevated flavinogenic activity. The investigation of the properties of three mutants with the highest flavinogenic activity, viz.

[Coordinate regulation of riboflavin permease and alpha-glucosidase synthesis in the yeast Pichia guilliermondii].

Riboflavin permease of the yeast Pichia guilliermondii appear to be inducible transport system. Its synthesis is induced by sucrose, maltose, alpha-methyl-D-glocoside, melizitose and raffinose, but not by D-glucose, trehalose or cellobiose. The synthesis of riboflavin permease in the presence of sucrose of maltose is depressed by cycloheximide, actinomycin D and 8-hydroxyquinoline.

[Effect of glucose and its derivatives on systems of riboflavin uptake and excretion in the yeast Pichia guilliermondii].

Riboflavin uptake by washed cells of riboflavin deficient mutant MS1-3 of Pichia guilliermondii yeast was strongly depressed by D-glucose, L-sorbose, alpha-methyl-D-glucoside, sucrose, trehalose, maltose and salicin but not by D-mannose, D-galactose, D-fructose or ribitol. Glucose decreased also the initial uptake rate of riboflavin analogue, 8-piperidyl-10-(1'-D-galactityl) isoalloxazine; the inhibition having a competitive character (Ki==5,7 mM). Apparently riboflavin permease is able to accept not only riboflavin and its analogues but also glucose and some of glucose derivates.

[Active transport of riboflavin in the yeast Pichia guilliermondii. Detection and some properties of the cryptic riboflavin permease].

In contrast to cells and protoplasts of the wild strain intact cells and protoplasts of riboflavin (RF)-deficient mutants of Pichia guilliermondii yeast possessing multiple sensitivity to antibiotics and antimetabolites were found capable to accomplish active transport of RF. The accumulation of RF against concentration gradient was energized by endogenous energy sources and was strongly depressed by uncouplers of oxidative phosphorylation and by inhibitors of respiration. RF transport was also blocked by the agents which destroy the permeability barrier and by sucrose.

[Riboflavin transport in cells of riboflavin-dependent yeast mutants].

Riboflavin was transported at a high rate into yeast cells of Pichia guilliermondii and Schwanniomyces occidentalis mutants capable of growth in a medium containing low concentrations of riboflavin, and having multiple susceptibility to some antibiotics and antimetabolites. Sucrose and sodium azide inhibited transport of riboflavin. Other riboflavin dependent mutants of Pichia guilliermondii, Pichia ohmeri, Torulopsis candida, and Saccharomyces cerevisiae, also growing in media containing low concentrations of riboflavin, were not capable of its active transport.

[Variability in the flavinogenic activity of Pichia guilliermondi yeasts].

The natural and induced variability of the flavinogenic activity was studied in the strain of Pichia guilliermondii ATCC 9058. The flavinogenic activity of the collection strain showed normal distribution; the amount of riboflavin(RF) accumulated in the medium differed several times in the extreme variants. In the clones with the maximum and minimum accumulation of RF, the distribution of the variants was asymmetric, due to the appearance of the cells with an average flavinogenic activity.

[Nature of riboflavin precursors in Pichia guilliermondi yeasts].

Thirty-nine riboflavin-deficient mutants have been isolated from three yeast strains of Pichia guilliermondii (ATSS 9058, VKM Y-1256, VKM Y-1257) and F5-121 mutant which is capable of production of large amounts of riboflavin in the presence of iron in the medium. All mutants were divided into five groups according to the nature of precursors accumulated in the medium and growth reaction in media with 6,7-dimethyl-8-ribityllumasine and diacetyl. The mutants of the first group did not accumulate specific precursors of riboflavin either in the cells or in the medium.