R. Maleszka

Enhanced rate of ethanol production from D-xylose using recycled or immobilized cells ofPachysolen tannophilus

SummaryEnhanced rates of ethanol production byPachysolen tannophilus from D-xylose were obtained by performing the fermentation with recycled cells in suspension culture or immobilized in a Ca-alginate gel. Fermentation under these conditions did not require aeration. Increasing temperature from 30 to 37°C enhanced the amount of ethanol produced in 24 hours from the recycled or the immobilized cells.

The requirement of oxygen for incorporation of carbon from d-xylose and d-glucose by Pachysolen tannophilus

Oxygen was required for growth of Pachysolen tannophilus on D-xylose, as well as on D-glucose. The reason was not identical to that of other yeasts whose anaerobic growth is stimulated by supplementation of the medium with lipids or organic hydrogen acceptors, as such supplements were ineffective with P. tannophilus. The requirement of oxygen was found to be due to its involvement in the incorporation of carbon from D-xylose, and to a large extent D-glucose as well, into trichloracetic acid-insoluble material. The role it played was associated with the channeling of catabolic intermediates into biosynthetic routes, since ethanol was formed anaerobically, but aeration was required for induction of several enzymes associated with the catabolism of D-xylose. The requirement suggested that normally functioning mitochondria were necessary for incorporation and growth, but not ethanol formation. This view was supported by the inability to obtain stable petite mutants, and by the effects of inhibitors of mitochondrial function, which caused effects on incorporation and growth under aerobic conditions similar to those of anaerobiosis.

YEASTS THAT FERMENT D-CELLOBIOSE AS WELL AS D-XYLOSE

SummaryYeasts that ferment both D-cellobiose and D-xylose have been identified. Such organisms may have advantages in the simultaneous saccharification and fermentation of cellulosics by obviating D-cellobiose inhibition of cellulase activity, and by allowing concurrent processing of the hemicellulose and cellulose.

Ethanol production from d-galactose and glycerol by Pachysolen tannophilus

Abstract Pachysolen tannophilus has recently been shown to be able to convert d -xylose, a pentose, to ethanol. Previously, d -xylose had been considered to be nonfermentable by yeasts. The present study shows that the organism can be used to obtain ethanol from other carbohydrates previously considered as nonfermentable, either by P. tannophilus in particular, d -galactose, or by yeasts in general, glycerol. Such identification for d -galactose allows P. tannophilus to be considered for fermentation of four of the five major plant monosaccharides: d -glucose, d -mannose, d -galactose and d -xylose. The ability to ferment glycerol is of potential use, in part, for the conversion of glycerol derived from algae into ethanol .

Ethanol production from various sugars by strains of Pachysolen tannophilus bearing different numbers of chromosomes

SUMMARY: Increasing chromosome number of Pachysolen tannophilus above the haploid level increased the yield of ethanol from D-xylose. There was a large increment on going from the haplophase to the diplophase, and the highest yields were obtained with either a triploid or a probable tetraploid, depending on the concentration of D-xylose. In addition, the rate of ethanol production from D-xylose and D-glucose increased, with the increment being larger on D-xylose. On D-galactose, the amount of ethanol produced within a given time also increased. The level of a by-product from D-xylose, xylitol, decreased on going from a haploid to higher ploidy, but there was no discernible trend for two other by-products, acetic acid and arabinitol. Increasing ploidy increased growth rate on D-galactose, but not appreciably on D-xylose. The altered properties on D-xylose of the strains tested were not due to increased levels of either D-xylose reductase or xylitol dehydrogenase, nor probably of alcohol dehydrogenase.

Involvement of oxygen and mitochondrial function in the metabolism of d-xylulose by Saccharomyces cerevisiae☆

Mitochondrial function associated with oxygen was required for growth of Saccharomyces cerevisiae on D-xylulose. The requirement was shown by (i) the inhibition of growth of a wild-type strain under anaerobic conditions, (ii) the inhibition of aerobic growth after treatment with inhibitors of mitochondrial function, and (iii) the lack of aerobic and anaerobic growth of nuclear and cytoplasmic petites. The mitochondrial function was associated with the channeling of catabolites of D-xylulose to growth processes, since ethanol was formed even when growth was inhibited. Mitochondrial function was implicated as well in determining the extent of growth and the concentration of ethanol in aerobic cultures of the wild-type. In such cultures, the concentration of ethanol decreased and growth increased concomitantly as aeration rate increased. A factor in this relation was considered to be the relatively poor ability of D-xylulose to inhibit the oxidative utilization of ethanol.

Mutants of Pachysolen tannophilus that produce enhanced amounts of acetic acid from D-xylose and other sugars

SummaryTwo mutants of Pachysolen tannophilus were isolated which produced considerably more acetic acid from several sugars than a wild type strain. Such mutants are of potential interest for the production of acetic acid rather than ethanol from lignocellulosic hydrolysates.