HIGH-CELL-DENSITY CULTIVATION OF YEASTS ON DISACCHARIDES IN OXYGEN-LIMITED BATCH CULTURES

Many facultatively fermentative yeast species exhibit a ''Kluyver effe ct'': even under oxygen-limited growth conditions, certain disaccharid es that support aerobic, respiratory growth are not fermented, even th ough the component monosaccharides are good fermentation substrates. T his article investigates the applicability of this phenomen on for hig h-cell-density cultivation of yeasts. In glucose-grown batch cultures of Candida utilis CBS 621,the onset of oxygen limitation led to alcoho lic fermentation and, consequently, a decrease of the biomass yield on sugar. In maltose-grown cultures, alcoholic fermentation did not occu r and oxygen-limited growth resulted in high biomass concentrations (9 0 g dry weight L(-1) from 200 g L(-1) maltose monohydrate in a simple batch fermentation). It was subsequently investigated whether this pri nciple could also be applied to Kluyveromyces species exhibiting a Klu yver effect for lactose. In oxygen-limited, glucose-grown chemostat cu ltures of K. wickerhamii CBS 2745, high ethanol concentrations and low biomass yields were observed. Conversely, ethanol was absent and biom ass yields on sugar were high in oxygen-limited chemostat cultures gro wn on lactose. Batch cultures of K. wickerhamii grown on lactose exhib ited the same growth characteristics as the maltose-grown C. utilis cu ltures: absence of ethanol formation and high biomass yields. Within t he species K. marxianus, the occurrence of a Kluyver effect for lactos e is known to be strain dependent. Thus, K. marxianus CBS 7894 could b e grown to high biomass densities in lactose-grown batch cultures, whe reas strain CBS 5795 produced ethanol after the onset of oxygen limita tion and, consequently, yielded low amounts of biomass. Because the us e of yeast strains exhibiting a Kluyver effect obviates the need for c ontrolled substrate-feeding strategies to avoid oxygen limitation, suc h strains should be excellently suited for the production of biomass a nd growth-related products from low-cost disaccharide-containing feeds tocks. (C) 1996 John Wiley & Sons, Inc.