High capacity xylose transport in Candida intermedia PYCC 4715

Xylose-utilising yeasts were screened to identify strains with high xylose transport capacity. Among the fastest-growing strains in xylose medium, Candida intermedia PYCC 4715 showed the highest xylose transport capacity. Maximal specific growth rate was the same in glucose and xylose media (mu(max)=0.5 h-1, 30 degrees C). Xylose transport showed biphasic kinetics when cells were grown in either xylose- or glucose-limited culture. The high-affinity xylose/proton symport system (Km = 0.2 mM, Vmax = 7.5 mmol h-1 g-1) was more repressed by glucose than by xylose. The less specific low-affinity transport system (K = 50 mM, Vmax = 11 mmol h-1 g-1) appeared to operate through a facilitated-diffusion mechanism and was expressed constitutively. Inhibition experiments showed that glucose is a substrate of both xylose transport systems.