Entomopathogenic bacteria to control mosquitoes are a promising environmentally friendly alternative to synthetic pesticides. In the present study, a novel mosquitocidal bacterium was isolated from marine soil collected from east coastal areas at Pondicherry (India). 16S rRNA gene sequence alignment depicted that this isolate belonged to Bacillus cereus VCRC-B520 (NCBI: KC-119192). Biochemical studies on bacterial growth, biomass, and toxin production have revealed that this strain could possibly be helpful in the production of a biopesticide in mosquito control. Toxicity assay with B. cereus against mosquito larvae has shown that the filariasis vector, Culex quinquefasciatus, is more susceptible than the other two species (Anopheles stephensi and Aedes aegypti). The LC50 and LC90 values for C. quinquefasciatus were 0.30 and 2.21 mg/L, respectively. No effect of B. cereus was found on nontargeted organisms. SDS-PAGE analysis and protein purification result from the cell mass of B. cereus have shown that a well-perceptible polypeptide was the dependable factor (85 kDa) for mosquitocidal action. Protein characterization (M/S MALDI-TOF) has shown that it is an endotoxin-specific insecticidal protein, namely "Cry4Aa". Phylogenetic analyses of 16S rDNA gene sequence from this marine isolate have revealed the presence of homology among closely related Bacillus strains. Therefore, considerable interest has been shown on the identification of a potential mosquitocidal bacterium from marine environment (B. cereus), which was not reported earlier in view of the current scenario of the rapid development of resistance to Bacillus sphaericus in mosquito vector control program.
A novel mosquitocidal bacterium was isolated from marine soil. 16S rRNA gene sequence alignment depicted that this isolate belonged to the strain, Enterobacter cloacae VCRC-B519 (NCBI: KC119193). Biochemical studies such as bacterial growth, biomass production and protein (toxin) synthesis showed that the strain is plausibly useful for mosquito control. It showed an increasing pattern of toxicity for Culex quinquefasciatus, Anopheles stephensi and Aedes aegypti, without negative effects for non-targeted organisms Chironomus riparius, Daphnia cephalata and Notonecta glauca. The qualitative analysis of the E. cloacae showed that three polypeptides (M.wt: 25, 30 and 50 kDa) were associated to the toxicity observed. The characterisation of these polypeptides (M/S MALDI-TOF)showed that they are enzymatic in nature. Consequently, the peptide sequences are identified to be polysugar degrading enzymes (25 kDa), cell wall associated hydrolases (30 kDa) and amino peptidase (50 kDa). Phylogenetic analyses of 16S rDNA gene sequence of E. cloacae revealed the occurrence of homology with closely related Enterobacter species. Therefore, it is concluded that the marine bacterium (Enterobacter cloacae)is possibly of use for the biological control of mosquito immatures.
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