A bifunctional cellulase–xylanase of a new Chryseobacterium strain isolated from the dung of a straw‐fed cattle. Issue 2 (4th December 2017) - Tan, Hao
Summary: A new cellulolytic strain of Chryseobacterium genus was screened from the dung of a cattle fed with cereal straw. A putative cellulase gene ( cbGH5 ) belonging to glycoside hydrolase family 5 subfamily 46 (GH5_46) was identified and cloned by degenerate PCR plus genome walking. The CbGH5 protein was overexpressed in Pichia pastoris, purified and characterized. It is the first bifunctional cellulase–xylanase reported in GH5_46 as well as in Chryseobacterium genus. The enzyme showed an endoglucanase activity on carboxymethylcellulose of 3237 μmol min −1 mg −1 at pH 9, 90 °C and a xylanase activity on birchwood xylan of 1793 μmol min −1 mg −1 at pH 8, 90 °C. The activity level and thermophilicity are in the front rank of all the known cellulases and xylanases. Core hydrophobicity had a positive effect on the thermophilicity of this enzyme. When similar quantity of enzymatic activity units was applied on the straws of wheat, rice, corn and oilseed rape, CbGH5 could obtain 3.5–5.0× glucose and 1.2–1.8× xylose than a mixed commercial cellulase plus xylanase of Novozymes. When applied on spent mushroom substrates made from the four straws, CbGH5 could obtain 9.2–15.7× glucose and 3.5–4.3× xylose than the mixed Novozymes cellulase+xylanase. The results suggest that CbGH5 could be a promising candidate for industrial lignocellulosic biomass conversion. Abstract : (i) high activity level and catalytic efficiency which are in the front rank of the known cellulases and xylanases; (ii) high thermophilicity (90 °C) that only a few cellulase or xylanase can be comparable with; (iii) using similar amount of enzymatic activity units, the enzyme could obtain much higher yield of glucose and xylose from both straw and spent mushroom substrate than a mixed commercial cellulase+xylanase of Novozymes.