Abstract

                                Xylitol is a functional sugar alcohol widely used as a sugar substitute. Chemical route of xylitol production is highly expensive, whereas microbial sources offer lower yield and conversion efficiency. In the present investigation, xylose reductase (XR) gene from Candida tropicalis GRA1 was cloned in pQE30Xa vector and transformed into E. coli M15. The resultant recombinant strain produced xylitol from xylose that harboured Xr gene transcribed under the control of lac operon. Such transcribed Xr protein converts xylose into xylitol using NADPH as a co-factor. Xylitol production was achieved by the recombinant E. coli M15 pQE30XrCt under shake-flask fermentation (2.1 g.l-1 in 24 h) with xylose as the sole substrate in the medium. Addition of co-substrate, glucose in the growth medium enhanced the xylitol production to the tune of 3.4g.l-1. Furthermore, the addition of co-substrate glycerol along with xylose enhanced a xylitol yield of 6.4g.l-1

Key words : Candida tropicalis, Xylose Reductase, E. coli M15, Xylose, Xylitol.