초록
<P><B>Abstract</B></P> <P>Wild-type <I>Corynebacterium glutamicum</I> has no endogenous metabolic activity for utilizing the lignocellulosic pentose <SMALL>D</SMALL>-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 <SMALL>D</SMALL>-xylose assimilation. In a previous study we found for <I>C. glutamicum</I> WMB by-product formation of xylitol during growth on <SMALL>D</SMALL>-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 <I>C. glutamicum</I>, we here show that this organism has a natural capability to synthesize xylitol from <SMALL>D</SMALL>-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 <I>C. glutamicum</I> ISO strain. Interestingly, low amounts of supplemented xylitol strongly inhibit growth of this strain on <SMALL>D</SMALL>-xylose, <SMALL>D</SMALL>-glucose and <SMALL>D</SMALL>-arabitol. These findings demonstrate that xylitol is a suitable substrate of the endogenous xylulokinase (XK, encoded by <I>xylB</I>) and its overexpression in the ISO strain leads to a significant phosphorylation of xylitol in <I>C. glutamicum</I>. Therefore, in order to circumvent cytotoxicity by xylitol-5-phosphate, the WMB pathway represents an interesting alternative route for engineering <I>C. glutamicum</I> towards efficient <SMALL>D</SMALL>-xylose utilization.</P> <P><B>Highlights</B></P> <P> <UL> <LI> <I>Corynebacterium glutamicum</I> accumulates extracellular xylitol during aerobic growth on <SMALL>D</SMALL>-xylose containing substrates. </LI> <LI> Intracellular xylitol is partly converted to cytotoxic xylitol-5-phosphatein <I>C. glutamicum</I> pEKEx3-<I>xylAXc</I>-<I>xylBCg</I> (ISO). </LI> <LI> Low amounts of supplemented xylitol strongly inhibit the growth of the ISO strain on <SMALL>D</SMALL>-xylose, <SMALL>D</SMALL>-glucose and <SMALL>D</SMALL>-arabitol. </LI> <LI> Xylitol is a suitable substrate of the endogenous xylulokinase(encoded by <I>xylB</I>). </LI> <LI> The Weimbergroute, operating independently from xylulokinase activity, could be an effective substitute towards efficient D-xylose utilization in <I>C. glutamicum</I>. </LI> </UL> </P>