Abstract
A cellulose-degrading bacterium originally isolated from gastrointestinal (GI) tract of Tibetan pig was identified as Bacillus subtilis BY-4 based on morphological features and 16S rDNA analysis. The B. subtilis BY-4 was found competent in utilizing wheat bran, corn powder, rice hull, wheat straw, and corn stover as energy sources. The strain can also be induced to multiply and produce acidic cellulase with a maximum cellulase activity of 8.61 U ml−1 on wheat bran after 48 h of cultivation. The cellulase exhibited relaxed substrate specificity for carboxymethylcellulose (CMC) and avicel, especially for corn powder, rice hull, chitosan, and wheat bran. The economical purification procedures, hydrophobic chromatography followed by gel filtration chromatography, generated 15.5-fold purified cellulase with 25.0% recovery. The molecular weight of the purified cellulase was estimated to be 55 kDa based on SDS-PAGE and zymogram analysis. The optimum values of pH and temperature on the purified cellulase response were found to be 4.5 and 60 °C, respectively. The cellulase can be activated by Mg2+ and Zn2+ but inhibited by Mn2+ and Co2+. Notably, intensive inhibitory action against Staphylococcus aureus was observed in the crude enzyme. The abovementioned properties, along with the generally recognized as safe (GRAS) Bacillus subtilis, are expected to enable potential applications of the BY-4 strain in the animal feed industry, such as acidic-cellulase production for the conversion of agriculture byproducts into animal feed.
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