Surfactin: a novel mosquitocidal biosurfactant produced by Bacillus subtilis ssp. subtilis (VCRC B471) and influence of abiotic factors on its pupicidal efficacy.

AIM: The rpoB gene of the mosquito pupicidal isolate Bacillus subtilis (VCRC B471) was amplified to confirm the subspecies as subtilis. The mosquito pupicidal activity expressed by the biosurfactant surfactin is novel, and hence, the influence of abiotic factors like pH, temperature of water and sunlight on its efficacy was studied under laboratory conditions.

METHODS AND

RESULTS

The rpoB gene amplicon of the bacterium (c. 570 bp of) was sequenced (accession number: EU057603). The relatedness of the bacterium to other members of the genus Bacillus was studied by tree construction, and the identity of VCRC B471 was confirmed as B. subtilis ssp. subtilis. The mosquito pupicidal activity exhibited by surfactin was found to be unaffected between pH 3-9, temperatures 25 and 37 °C and exposure to sunlight/UV radiation. Further, the pupicidal activity of surfactin was not diminished after exposure to 121 °C for 15 min, indicating its thermostable nature.

CONCLUSIONS

VCRC B471 is confirmed as a strain of B. subtilis ssp. subtilis. The mosquitocidal toxin, surfactin produced by this bacterium being stable to UV and varied temperature, active at acidic and basic pH and temperatures between 25 and 42 °C renders this molecule an interesting lead to be developed as a mosquitocidal agent.

SIGNIFICANCE AND IMPACT OF THE STUDY: The mosquitocidal toxin, surfactin produced by B. subtilis ssp. subtilis (VCRC B471), being a biodegradable biosurfactant, exhibiting high stability to varied environmental conditions, can be used year round in breeding habitats and will be a prospective microbial toxin for use against mosquitoes.