Phosphate limitation stress induces xylitol overproduction byDebaryomyces hansenii

Abstract

The physiological responses of xylose‐grown Debaryomyces hansenii were studied under different nutritive stress conditions using continuous cultivation at a constant dilution rate of 0.055 h−1. Metabolic steady‐state data were obtained for xylose, ammonium, potassium, phosphate and oxygen limitation. For xylose and potassium limitation, fully oxidative metabolism occurred leading to the production of biomass and CO2 as the only metabolic products. However, potassium‐limiting cultivation was the most severe nutritional stress of all tested, exhibiting the highest xylose and O2 specific consumption rates along with the lowest biomass yield, 0.22 g g−1 xylose. It is suggested that carbon was mainly channelled to meet the cellular energy requirements for potassium uptake. For the other limiting nutritional conditions increasing amounts of extracellular xylitol were found for ammonium, phosphate and oxygen limitation. Although xylitol excretion is not significant for ammonium limitation, the same is not true for phosphate limitation where the xylitol productivity reached 0.10 g l−1 h−1, about half of that found under oxygen‐limiting conditions, 0.21 g l−1 h−1. This work is the first evidence that xylitol production by D. hansenii might not only be a consequence of a redox imbalance usually attained under semi‐aerobic conditions, but additional physiological mechanisms must be involved, especially under phosphate limitation. Cell yields changed drastically as a function of the limiting nutrient, being 0.22, 0.29, and 0.39 g g−1 xylose for potassium, oxygen and phosphate limitation, respectively, and are a good indicator of the severity of nutritive stress.

Yeast Biomass Production in Brewery’s Spent Grains Hemicellulosic Hydrolyzate

“…Carbohydrate content was higher than the values reported for C. langeronii [8], and K. fragilis [23], but in the range of C. blankii [6]. These values are typical of carbon excess growth conditions for this yeast [33], and hence they can be further improved, namely, the protein content.…”

Pulsed electric field: A “green” extraction technology for biomolecular products from glycerol with fermentation of non-Saccharomyces yeasts

“…The first is a direct hydroxyl elimination leading to purivate derivatives propane diols, the second is an isomerization of glycose to maltitol and other polyols and the last one is from Frontiers in Bioengineering and Biotechnology frontiersin.org ribulose 5-phosphate, as shown in Figure 2. In the work of Tavares et al (1999) it is shown for the first time that xylitol production by the yeast Debaryomyces hansenii is not only a result of a redox balance usually occurred under poor aerobic conditions, but also that there are additional physiological mechanisms involved, mainly from phosphate limitation.…”