Efficient cofermentation of hexose and pentose sugars is essential for ABE (Acetone, Butanol and Ethanol) solvents production from lignocellulosic hydrolysates by Clostridium acetobutylicum, an important industrial microorganism. However, utilization of xylose, the predominant pentose present in lignocellulosic feedstocks, by this anaerobe is limited by CCR (Carbon Catabolite Repression) 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 C. acetobutylicum. 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 sol genes (ctfA, ctfB and adhE1) 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 72 h when fermenting a mixture of glucose and xylose (30 g/L glucose and 15 g/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 C. acetobutylicum CcpA with alleviated repression on xylose metabolism, yielding a valuable platform host toward ABE solvents production from lignocellulosic biomass.
Keywords: C. acetobutylicum; CcpA mutagenesis; Sol overexpression; Xylose and glucose cofermentation.
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