The Catabolism of Acyclic Polyols by Yeasts

SUMMARY: Eight polyols were employed in turn as sole carbon source for aerobic growth tests with sixteen yeasts. The yeasts studied varied from those using none to others using all the polyols. Mean generation times in aerated, liquid, shaken medium for five yeasts and four polyols, were from 2 to 7.5 hr. With seven yeasts, oxygen uptake was measured for different polyols as sole carbon source, of washed, starved yeast cells, harvested in the exponential phase of growth. No yeast respired a substrate on which it did not grow, or vice versa. Except when glucose, erythritol or galactitol (dulcitol) were employed, respiration rates were not greatly affected by the carbon source for growth. Coenzyme-linked polyol dehydrogenase activity was measured with crude cell-free extracts of four yeasts and several polyols or sugars. The enzymes had a low affinity for their substrates. In certain cases the polyol oxidation products were examined chromatographically. The polyol dehydrogenases of four yeasts were separated from crude cell extracts by gel electrophoresis, and detected on the gels by their activity with different polyols, and with NAD+ or NADP+. One strain of Torulopsis candida appears to synthesize at least eight polyol dehydrogenases which differ in their specificity for polyols, coenzyme or inducer. Similarly, four polyol dehydrogenases were found in a strain of Candida utilis. Most of these enzymes were inducible. There was no evidence that phosphorylation was the first step in polyol catabolism. From experiments with 14C-labelled polyols, it seems that Candida utilis and Pichia membranaefaciens do not utilize D-glucitol (sorbitol) or D-mannitol because these substrates do not enter the yeast cells.