Optimization and characterization of extracellular cellulase produced by Bacillus pumilus MGB05 isolated from midgut of muga silkworm (Antheraea assamensis Helfer)

Mature larvae of Antheraea assamensis were collected from different locations of Assam to isolate the cellulolytic gut microflora. Altogether sixty cellulase degrading bacteria were isolated on agar plates containing micro-crystalline cellulose as the sole carbon source. Among them, ten isolates showed hydrolyzing zone on agar plates containing carboxy methyl cellulose (CMC) after staining with Congo-red. Isolate MGB05 exhibited the highest CMCase activity (0.262 U/mL) at 72 h of incubation under submerged condition. FPase and beta-glucosidase activity were 0.012 U/mL and 3.71 U/mL respectively. It showed maximum FPase (0.022 U/mL) activity on the 3rd day of incubation in the media containing wheat bran as a carbon source. beta-glucosidase production was also found to be highest with wheat bran (20.03 U/mL) at 48 h of incubation. The optimum pH and temperature of FPase activity of MGB05 were found at 6.0 and 50 degrees C respectively while for beta-glucosidase activity, it was maximum at pH 6.0 under 50 degrees C. In addition, metal ion Mg++ and Ca++ enhanced FPase activity up to 110.92% (0.026 U/mL) and 105.31% (0.025 U/mL) respectively. In-vitro antimicrobial bioassay of the most potent cellulolytic bacteria (MGB05) also showed high antimicrobial activity against Escherichia cob (2.9 cm) and Pseudomonas aeruginosa (3.0 cm). The isolate MGB05 has been identified based on 16S rDNA homology as Bacillus pumilus MGB05 with accession KP298708.2. Results encompass the prospective beneficial role of gut-microflora on digestion and disease resistance. which might be a potential probiotic component to enhance silk productivity.