The Catabolism of Acyclic Polyols by Yeasts

Abstract

S U M M A R YEight 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 NADS-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. INTRODUCTIONDifferences between yeasts in their ability to use polyols as sole carbon sources for aerobic growth have been employed for classifying and identifying yeasts (e.g. Wickerham, 1951;Kudriavzev, 1954;Kreger-van Rij, 1964;Poncet & Arpin, 1965 The polyol phosphate, formed in reaction (c), may be oxidized to give a sugar phosphate by reactions analogous to (a) and (b). The sugars or sugar phosphates formed from the polyols are probably metabolized by the Embden-Meyerhof pathway or the pentose cycle.All-or-none differences in the ability of yeasts to utilize polyols presumably reflect the presence or absence of (i) enzymes necessary to metabolize the polyols, or (ii) mechanisms for the entry of the polyols into the yeast cells. The present paper reports investigations of biochemical systems which may underlie differences between yeasts in their utilization of polyols.The aim of this work was to study a number of yeasts and to relate differences in the behaviour of whole organisms to differences between their internal mechanisms. There are, however, special difficulties in showing why one yeast uses a particular substrate for growth and respiration, and another does not. For example, Pichia delftensis can grow on ribitol, D-glucitol or D-mannitol, whilst P. membranaefaciens cannot grow on any of the polyols ( T...

Growth and Metabolism of Mannitol by Strains of Saccharomyces cerevisiae

“…cerevisiae for growth on mannitol Of the 40 polyploid strains of S. cereuisiae screened (Table l), 20 were capable of good growth (5-20mg dry wt ml-*) on 5 % mannitol. It may therefore be concluded that the generally held view that S. cereuisiae cannot grow on mannitol (Barnett, 1968;Spoerl & Doyle, 1968) mannitol (van der Walt, 1970). It is unfortunate that the methods used by taxonomists for the measurement of growth are semi-quantitative so that direct comparison with the work reported here cannot be made.…”

“…cerevisiae (Wolff & Kaplan, 1956), neither being grown on mannitol. However, taxonomists have noted that some strains of S. cerevisiae can assimilate mannitol (van der Walt, 1970), although in a more recent text (Barnett et al, 1983) growth was reported either not to occur or to occur after a delay of 14-21 d. More specifically, growth of S. cerevisiae on mannitol has been suggested (Kirsop, 1974) or shown (Wiles, 1953;Quain, 1986) to be useful in the differentiation of brewing yeasts.…”

“…Others have shown mannitol to be transported but not metabolized (Spoerl & Doyle, 1968;Maxwell & Spoerl, 1971 ;Canh et al, 1975). In a detailed study of the catabolism of a number of acyclic polyols by 16 yeasts, Barnett (1968) found the strain of S. cerevisiae tested to be incapable of growth on mannitol or other polyols. However, Tyson et al (1979) reported doubling times and cell size of S. cerevisiae S288C grown on a wide range of carbon sources, including mannitol and another acyclic polyol, sorbi tol.…”

Candida sorbosivorans sp. nov., a new member of the genus Candida Berkhout.

“…$ 0n3. Each growth was measured at least four times at 640 nm and calibrated in terms of dry weight (Barnett, 1968). Doubling times were calculated from the linear relationship between the logarithm of dry weight and time, during exponential growth.…”

The Effects of Different Carbon Sources and Changes in the Growth Medium on the Shape of Cells of the Yeast Trigonopsis variabilis

“…Each flask was inoculated with about I mg dry wt of yeast from a I-day-old YM agar slope, and was incubated in a Gallenkarnp Orbital shaker at 175rev./min. Growth was measured with a nephelometer, calibrated in terms of dry weight (Barnett, 1968) about every 10 h during growth. Each experiment was done at least twice.…”