Growth parameters for optimizing the cultivation of Bacillus thuringiensis (Berliner, 1911) isolates to control Aedes aegypti (Linnaeus, 1762)

Objective: To obtain the growth parameters of Bacillus thuringiensis (Bt) strains active against Aedes aegypti. Methods: Eighteen combinations of pH and temperatures were tested to determine the best growth conditions for three isolates from the Maranhão Entomopathogenic Bacillus Bank: BtMA-690, BtMA-750, and BtMA-1114. To confirm the best growth conditions, the inoculum was quantified by measuring the spore concentration (spores/mL) and cell mass (g/L). The LC50 of the isolates grown under extreme temperature conditions and the two best growth conditions were tested in bioassays with A. aegypti larvae to confirm toxicity. Results: Isolates BtMA-690 and BtMA-750 showed the best growth conditions at 34°C with pH 8.0 for spore concentration and 30°C with pH 6.0 for cell mass. In contrast, BtMA-1114 exhibited better growth at 28°C with pH 7.0 for spore concentration and 34°C with pH 6.0 for cell mass. After 72 hours, BtMA-690 showed a mortality of 35%, in the combination 26°C with pH 6.0, BtMA-750 above 90% for nine of the conditions tested and BtMA-1114 with 14%, for 36°C with pH 7.0. Conclusion: Optimizing the growth of Bt strains in the laboratory will enable better adjustment of growth parameters for the cultivation of these isolates.