Roy J. Thornton

Factors influencing the utilisation of L-malate by yeasts.

The utilisation of L-malate and the effect of glucose concentration on malate utilisation under semi-anaerobic conditions were investigated in three yeasts unable to grow on malate as sole carbon source (Saccharomyces cerevisiae, Schizosaccharomyces malidevorans, Zygosaccharomyces bailii) and two yeasts able to utilise the TCA cycle intermediate as sole carbon source (Pichia stipitis and Pachysolen tannophilus). Utilisation of malate by both Schiz. malidevorans and Z. bailii was reduced at high and low levels of glucose. In the absence of glucose, P. stipitis and Pa. tannophilus utilised malate rapidly; however, their utilisation was drastically reduced in the presence of glucose, suggesting that malate utilisation is under catabolite repression.

Strain improvement of the xylose-fermenting yeastPachysolen tannophilus by hybridisation of two mutant strains

Two previously reported mutants ofPachysolen tannophilus, which accumulate ethanol more rapidly and in greater yield than the wild-type NRRL Y2460, have been cross-mated. Aneth 2-1 mutant which is unable to grow on ethanol, was mated with the mutant NO3−NO3-4 which possesses increased levels of pentose phosphate pathway enzymes. The new hybrid strain combines the properties of both parents and possesses improved characteristics for xylose fermentation to ethanol.

A malic acid dependent mutant of Schizosaccharomyces malidevorans

The yeast Schizosaccharomyces malidevorans utilizes l-malate when grown on glucose as the carbon source. A mutant of this yeast has been isolated which is dependent on the presence of both l-malate and glucose for growth. The mutant utilizes l-malate as rapidly as the wildtype and the utilization of glucose is greatly reduced. Other TCA cycle intermediates do not relieve the malate dependence.

Transformation of a glucose negative mutant ofPachysolen tannophilus with a plasmid carrying the cloned hexokinase PII gene fromSaccharomyces cerevisiae

Lithium treated cells of the yeastPachysolen tannophilus have been transformed with a plasmid carrying the gene encoding for the hexokinase PII enzyme fromSaccharomyces cerevisiae. The gene was expressed and the presence of the enzyme within the cell was demonstrated by DEAE-cellulose chromatography of cell-free extracts. Plasmid DNA from the transformants was used to transformE. coli HB101. Plasmid DNA from the bacterial transformants had the same mobility on an agarose gel as the original plasmid.

Effect of chromium on the rate of carbon dioxide evolution fromSaccharomyces cerevisiae

Abstract The rate of carbon dioxide evolution by whole yeast cells was measured under conditions of both chromium starvation and availability. Preincubation experiments show that there is no evidence for the view that Saccharomyces cerevisiae can synthesize a biologically important form of chromium from simple chromium(III) salts. Chromium enters the yeast cell, possibly by way of the glucose transport system, and exerts a slight inhibitory effect on the fermentation rate but does not affect the rate of cell growth. Glucose tolerance factor fractions show a stimulatory effect in the yeast fermentation assay irrespective of whether the yeast is chromium depleted. The evidence shows that chromium is not an essential trace element for normal yeast metabolism and hence the activity of glucose tolerance factor preparations is unlikely to be due to a chromium complex as is commonly assumed. Some other as yet unidentified compound or compounds must be responsible for the observed increase in the rate of carbon dioxide evolution.

Mapping of ure1, ure2 and ure3 Markers in Fission Yeast

The following urease genes of the fission yeast Schizosaccharomyces pombe have been mapped by induced haploidization and tetrad analysis—ure1: chromosome arm III‐L; ure2 and ure3: chromosome arm I‐R. The previously determined tps19–rad1 interval (11–12 cM) has been increased to 18 cM. A convenient medium for rapidly scoring the ure gene markers of fission yeast was developed.