초록
<P><B>Abstract</B></P> <P>Efficient cofermentation of hexose and pentose sugars is essential for ABE (<I>A</I>cetone, <I>B</I>utanol and <I>E</I>thanol) solvents production from lignocellulosic hydrolysates by <I>Clostridium acetobutylicum</I>, an important industrial microorganism. However, utilization of xylose, the predominant pentose present in lignocellulosic feedstocks, by this anaerobe is limited by CCR (<I>C</I>arbon <I>C</I>atabolite <I>R</I>epression) that is mediated by the catabolite control protein A (CcpA). Here, we reported a novel engineering strategy based on CcpA molecular modulation to overcome the defect. Through CcpA mutagenesis and screening, an amino acid residue, valine 302, was shown to be essential for CcpA-dependent CCR in <I>C. acetobutylicum</I>. When this residue was replaced by asparagine (V302N mutation), CCR could be alleviated and a greatly improved xylose utilization was realized. Transcriptional and DNA binding analysis was then used to elucidate the underlying molecular mechanism. Furthermore, the <I>sol</I> genes (<I>ctfA</I>, <I>ctfB</I> and <I>adhE1</I>) were overexpressed, upon the V302N mutation, to accelerate sugar consumption and solvents formation. The resulting strain (824ccpA-V302N-sol) was capable of using over 90% of the total xylose within 72h when fermenting a mixture of glucose and xylose (30g/L glucose and 15g/L xylose), which was much higher than that (30%) of the control strain 824ccpA-ccpA(C). This is the first report that offered an optimized <I>C. acetobutylicum</I> CcpA with alleviated repression on xylose metabolism, yielding a valuable platform host toward ABE solvents production from lignocellulosic biomass.</P> <P><B>Highlights</B></P> <P> <UL> <LI> The first report to alleviate CCR in clostridia via CcpA modulation. </LI> <LI> Obtaining a CcpA mutant with alleviated “glucose repression” on xylose utilization. </LI> <LI> Overexpression of <I>sol</I> genes further improved the performance of the CcpA mutant. </LI> <LI> The CcpA mutant is a useful host for further genetic modification. </LI> </UL> </P>