Screening and Characterization of Flocculent Yeast, Candida sp. HY200, for the Production of Xylitol from D-Xylose

On the basis of high osmotic tolerance and xylitol production, a novel yeast strain was screened from soils of rice farming. The isolated strain HY200 was systematically characterized by using general approaches of Biolog Microlog$^{TM}$ and 18S rRNA sequence analyses, and consequently was designated as Candida tropicalis HY200. Under formulated culture conditions, relatively high xylitol yield ($77\%$) and productivity (2.57 g/l$\codt$h) were obtained, in practice, when 200 g/l of xylose was supplemented. In the utilization of nitrogen, inorganic compounds could not serve as nitrogen sources. As a promising phenotype, HY200 steadily flocculated during and/or after growing in the formulated medium. The extent of flocculation was partly affected by nitrogen sources. However, regardless of the kinds of carbon source fed, the flocculent cells were always observed at the end of the exponential growth phase. These observations strongly suggest that the strain HY200 could effectively be used as a potential candidate for the production of xylitol from xylose, especially in repeated batch mode, because of its flocculation ability and tolerance to high substrate concentrations.