Bioprospecting of an Indigeneous Bacillus thuringiensis Strain G5-8-3T02 for Shrimp Culture System

Aim: An indigenous Bacillus thuringiensis strain G5-8-3T02 earlier isolated from healthy shrimp intestine and established to safeguard Penaeus monodon from Vibrio mimicus infection was assessed as a potential candidate bacterium for drug enhancement for shrimp culture systems.

Methodology: Optimal temperature, pH and salinity for growth and antibacterial activity of Bacillus thuringiensis against Vibrio mimicus were determined. The effects of enzymes (pepsin, catalase, lipase and α- amylase), pH (2-9), heat (37°C – 121°C) and surfactants (Sodium dodecyl sulphate and Tween 80) on antibacterial activity were also evaluated. Cell growth and antibacterial activity were monitored daily for 5 days via spectrophotometric method at 600 nm and agar well diffusion assay respectively. The metabolite extracted with methanol was analyzed for bioactive compounds using Gas Chromatography-Mass Spectrometry (GC-MS).

Results: The optimum temperature, pH and salinity for growth and metabolite production were 35°C, pH 6-7 and 10-15 ppt. respectively. The crude extract did not totally lose its activity when treated with enzymes, various pH values, heat and surfactants. The quantitative composition of the metabolite revealed 15 bioactive compounds. The main compound produced was 2, 6, 10-Trimethyltridecane with peak area of 14.58%.

Conclusion: The non-pathogenic, antagonistic, indigenous Bacillus thuringiensis strain G5-8-3T02 could be engaged in the management of vibriosis in shrimp culture since the use of antibiotics in aquaculture for disease control yields objectionable effects. The identified bioactive compounds might be valuable for drug development for shrimp culture system.