The major aspect of immune system in insects can be attributed to its humoral immune response that is largely operated by means of some defense proteins or antimicrobial peptides. Muga silkworms have remained mostly unexplored in this matter, and as such in this study, Bacillus thuringiensis inoculated fifth-instar muga silkworm larva was analyzed for changes in protein profile, antimicrobial activity, as well toxicity assessment of the bacteria in the body of the silkworm larvae. Toxicity assessment was done by the serial dilution method, which was used to prepare various bacterial doses, and the LC50 value was found to be at 5.7 × 106 CFU/mL. A sublethal concentration was used for immunization of the larvae, following which hemolymph from the silkworms were collected at different time intervals, that is, 6 h, 12 h, 18 h, and 24 h. Antimicrobial assessment by well diffusion method showed the hemolymph collected after 24 h to be potent against both B. thuringiensis (MTCC 1953) and Escherichia coli (MTCC 40). Furthermore, analysis of this hemolymph revealed higher concentration of protein content as well as higher free amino acid concentration compared with a normal group. The appearance of several new bands in SDS-PAGE analysis of the same hemolymph was observed, which was not seen in the protein profile of normal silkworm previously. Proper proteomic analysis and characterization of such proteins produced on immunization might prove to be revolutionary in better understanding the silkworm as well as its defense mechanism providing valuable insights. This might be crucial for the development of natural and potent antibiotics with fewer side effects.
Key words: Amino acid, AMPs, Bacillus thuringiensis, Haemolymph, Muga silkworm, SDS-PAGE.
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