Oxygen starvation induces cell death in Candida shehatae fermentations of D-xylose, but not D-glucose

Candida shehatae cells, cultivated on D-glucose and D-xylose, were subjecte d to a shift from fully aerobic to anaerobic fermentative conditions. After anaerobic conditions were imposed, growth was limited to approximately one doubling or less as C, shehatae rapidly entered a stationary phase of grow th. Following the shift to anoxia, cell viability rapidly declined and the total cell volume declined in the D-xylose fermentations. Moreover, the cel l volume distribution shifted to smaller volumes. Cell viability, measured by plate counts, declined nine times faster for D-xylose fermentations than for D-glucose fermentations. Anaerobic growth did not occur on either D-gl ucose or D-xylose. Selected vitamins and amino acids did not stimulate anae robic growth in C. shehatae, but did enhance anaerobic growth on D-glucose in S, cerevisiae. The decline in cell viability and lack of anaerobic growt h by C. shehatae were attributed to oxygen deficiency and not to ethanol in hibition. The results shed light on why C, shehatae anaerobic fermentations are not currently practical and suggest that research directed towards a b iochemical understanding of why C. shehatae can not grow anaerobically will yield significant improvements in ethanol fermentations from D-xylose.