Increase in xylitol production by Candida tropicalis upon addition of salt

We examined the effect of salt on xylitol production by a 559-9 strain of Candida tropicalis. The addition of several different salts, including NaCl, KCl, and MgCl2, increased xylitol production. Upon the addition of 4% NaCl, the maximum yield of xylitol from 5% -xylose increased by about 1.3-fold. This effect of NaCl was reduced with increasing -xylose concentrations in the medium. On the other hand, xylitol production is known to be suppressed in the presence of -glucose. The addition of salts also increased the xylitol production even in the presence of 2% -glucose. For example, the maximum yield of xylitol increased by about 1.6-fold upon addition of NaCl. These findings suggest that the addition of salt may be an effective means of increasing xylitol production when the hydrolysates of cellulosic materials, which contain low concentrations of -xylose and -glucose, are used as a substrate. Production of NADPH-dependent xylose reductase in cells grown on media containing 5% -xylose increased upon addition of 4% NaCl. The increase in xylitol production by NaCl may be due in part to the increase in xylose reductase production.