RAPD-PCR characterization of Bacillus thuringiensis soil isolates from Mizoram with insecticidal activity against Culex tritaeniorhynchus

Abstract

Background & Aim: Vector-borne diseases are one of the major public health problems in developing countries. Culex
tritaeniorhynchus (Diptera: Culicidae) could be a vector of filariasis and West Nile encephalitis. The use of
entomopathogenic bacteria like Bacillus thuringiensis (Bt) as larvicides is a viable alternative for the biological control
mosquitoes with a low environmental impact. Hence, an attempt was made to explore the abundance of Bt in Mizoram
soils from different habitats, testing their toxicity against C. tritaeniorhynchus and characterization by following acetate
selection, mortality, dissimilarity analysis and RAPD-PCR assay methods. Method: In this present study, nine soil
isolates (Mzubt 2,4,5,6,11,23,25,26 and 29) were identified, characterized and evaluated against C. tritaeniorhynchus.
The new isolates were compared with two reference strains - Bt israelensis 4Q1 and Bt aizawai 4J3 obtained from
Bacillus Genetic Stock Center, USA. Results: The mzubt 2 and mzubt 6 isolates showed higher larvicidal activity than
other isolates, against C. tritaeniorhynchus. RAPD-PCR assay has been optimized that discriminate Bacillus
thuringiensis (Bt) isolates from nine different habitats soil covering five districts of Mizoram. All the studied isolates
showed a diverse RAPD patterns and were different from each other in relation to habitats, toxicity and type of cry gene
present. High polymorphism was observed between Bt isolates which was authenticated through high PIC, RP, EMR and
MI values. Further, three major clusters were identified through dissimilarity analysis. Conclusion: No relationship
found between the type of cry gene in Bt and their toxicity against mosquitoes. The importance of the isolation of native
strains of Bt in the mosquito management program in Mizoram is highlighted based on the findings.