Biotechnological potential of Candida spp. for the bioconversion of D-xylose to xylitol

In the present study, 28 yeast isolates were obtained from sugarcane filter cake material collected across several ethanol industrial areas located in the State of Sao Paulo, Brazil. First, isolates were taxonomically affiliated by sequencing and analysis of the D1/D2 region of the 26S rRNA gene as Candida tropicalis (24 isolates) and Candida rugosa (four isolates). Second, five phylogenetically distant isolates were selected and quantitatively tested for their capacity to bioconvert D-xylose to xylitol (C. tropicalis MVP 03, C. tropicalis MVP 16, C. tropicalis MVP 40, C. rugosa MVP 17 and C. rugosa MVP 21). The fermentation processes yielded xylitol production ranging from 5.76 to 32.97 g L-1, from an initial D-xylose concentration of 50 g L-1, with the volumetric production (Qp) ranging from 0.06 to 0.35 g L-1 h-1. The measurement of these parameters allowed the determination of the conversion efficiency of D-xylose to xylitol (h), which showed values ranging from 6 to 61%. Remarkable, the yeast isolate C. tropicalis MVP 16 presented the highest efficiency among tested lines, yielding up to 32.97 g L-1 of xylitol (Qp = 0.35 g L-1 h-1, h = 61%) after 96 h of fermentation. These results describe the biotechnological potential of yeast populations naturally occurring in filter cake substrates. Further studies at the genomic level are required, in order to enhance our understanding on yeast metabolisms involved in the xylitol bio-conversion/production, a currently high-added-value product. Key words: Fermentation efficiency, 26S rRNA gene, yeast isolates, sugarcane residues.