Phosphate limitation stress induces xylitol overproduction by Debaryomyceshansenii

The physiological responses of xylose-grown Debaryomyces hansenii were stud ied under different nutritive stress conditions using continuous cultivatio n at a constant dilution rate of 0.055 h(-1). Metabolic steady-state data w ere obtained for xylose, ammonium, potassium, phosphate and oxygen limitati on. For xylose and potassium limitation, fully oxidative metabolism occurre d leading to the production of biomass and CO2 as the only metabolic produc ts. However, potassium-limiting cultivation was the most severe nutritional stress of all tested, exhibiting the highest xylose and O-2 specific consu mption rates along with the lowest biomass yield, 0.22 g g(-1) xylose. It i s suggested that carbon was mainly channelled to meet the cellular energy r equirements for potassium uptake. For the other limiting nutritional condit ions increasing amounts of extracellular xylitol were found for ammonium, p hosphate and oxygen limitation. Although xylitol excretion is not significa nt for ammonium limitation, the same is not true for phosphate limitation w here the xylitol productivity reached 0.10 g 1(-1) h(-1), about half of tha t found under oxygen-limiting conditions, 0.21 g 1(-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 con ditions, but additional physiological mechanisms must be involved, especial ly under phosphate limitation. Cell yields changed drastically as a functio n of the limiting nutrient, being 0.22, 0.29, and 0.39 g g(-1) xylose for p otassium, oxygen and phosphate limitation, respectively, and are a good ind icator of the severity of nutritive stress. (C) 1999 Federation of European Microbiological Societies. Published by Elsevier Science B.V. All rights r eserved.