Mosquitocidal Bacillus amyloliquefaciens: Dynamics of growth & production of novel pupicidal biosurfactant

BACKGROUND & OBJECTIVES A strain of Bacillus amyloliquefaciens (VCRC B483) producing mosquito larvicidal and pupicidal biosurfactant was isolated from mangrove forest soil. The present study was aimed at studying the kinetics of growth and production of the mosquitocidal biosurfactant by this bacterium. METHODS Dynamics of growth, sporulation and production of mosquitocidal biosurfactant were studied by standard microbiological methods. The mosquitocidal biosurfactant was precipitated from the culture supernatant and bioassayed against immature stages of mosquito vectors to determine lethal dose and lethal time. The activity, biological and biochemical properties of the biosurfactant have also been studied. RESULTS The pupal stages of mosquitoes were found to be more vulnerable to the biosurfactant produced by this bacterium with Anopheles stephensi being the most vulnerable species. The median lethal time (LT 50 ) was found to be 1.23 h when the pupal stages of the above species were exposed to lethal concentration LC 90 (9 µg/ml) dosage of the biosurfactant. Production of biosurfactant was found to increase with incubation time and maximum biomass, maximum quantity of biosurfactant (7.9 mg/ml), maximum biosurfactant activity (6 kBS unit/mg) and maximum mosquitocidal activity (5 µg/ml) were attained by 72 h of growth. The lipopeptide nature of the biosurfactant was confirmed by β-haemolysis, lipase activity, biofilm forming capacity, thermostability and biochemical analysis. INTERPRETATION & CONCLUSIONS The mosquitocidal biosurfactant produced by B. amyloliquefaciens (VCRC B483) may be a prospective alternative molecule for use in mosquito control programmes involving bacterial biopesticides.