Formation of xylitol and xylitol-5-phosphate and its impact on growth of D-xylose-utilizing Corynebacterium glutamicum strains

Wild-type Corynebacterium glutamicum has no endogenous metabolic activity for utilizing the lignocellulosic pentose D-xylose for cell growth. Therefore, two different engineering approaches have been pursued resulting in platform strains harbouring a functional version of either the Isomerase (ISO) or the Weimberg (WMB) pathway for D-xylose assimilation. In a previous study we found for C. glutamicum WMB by-product formation of xylitol during growth on D-xylose and speculated that the observed lower growth rates are due to the growth inhibiting effect of this compound. Based on a detailed phenotyping of the ISO, WMB and the wild-type strain of C. glutamicum, we here show that this organism has a natural capability to synthesize xylitol from D-xylose under aerobic cultivation conditions. We furthermore observed the intracellular accumulation of xylitol-5-phosphate as a result of the intracellular phosphorylation of xylitol, which was particularly pronounced in the C. glutamicum ISO strain. Interestingly, low amounts of supplemented xylitol strongly inhibit growth of this strain on D-xylose, D-glucose and D-arabitol. These findings demonstrate that xylitol is a suitable substrate of the endogenous xylulokinase (XK, encoded by xylB) and its overexpression in the ISO strain leads to a significant phosphorylation of xylitol in C. glutamicum. Therefore, in order to circumvent cytotoxicity by xylitol-5-phosphate, the WMB pathway represents an interesting alternative route for engineering C. glutamicum towards efficient D-xylose utilization. (C) 2016 Elsevier B.V. All rights reserved.