Toxicidade, caracterização molecular de bacillus sphaericus da amazônia e parâmetros do crescimento microbiano para a produção de bioinseticida.

Abstract

Larvicidal activity of B. sphaericus from several places in Amazonia, was estimated to Anopheles darlingi and Culex quinquefasciatus. Pobit analysis was used to determine the median lethal concentration (LC50) and potency relative to the 2362 standard strain. Findings pointed out strains IB15 (LC50 = 0.040 ppm), IB19 and S1116 (LC50 = 0.048 ppm), IB16 (LC50 = 0.052 ppm) and S265 (LC50 = 0.057 ppm) as the most effective ones, being IB15 with a potency of close to 50%, higher to strain 2362 in the assays carried out with A. darlingi. IB16 and S1116 were more potent in the experiments with C. quinquefasciatus, showing to be nearly 300-400% higher. Through molecular characterisation were diagnosed the binary toxin gene in all twenty studied stains and MTX1 toxin was found only on fourteen of them. Twenty-three polymorphic sites on the sequences were observed on the basis of the BinA sequences, being only four of them informative for the parsimony. As a whole, ten haplotypes were obtained amongst the Amazonian strains, being haplotype 1 (nine strains) similar to that of 2362 (Type 2) and the rest presenting distinct sequences. The 16 polymorphic sites observed on the aminoacid sequences resulted into 19 variant aminoacids and, on the basis of the genetic distance among the strains, it was not possible to establish a correlation between variations on BinA toxin sequences and toxicity level, as well as precedence of the strains. As B. sphaericus raises biotechnological interest in the production of biolarvicides, IB15 strain microbial growth in NYSM medium during 24h of fermentation, was studied. It was found that IB15 presented a growth profile similar to 2362 strain to prduction of cells, spores, biomass and larvicidal activity throughout fermentation, with no statistically significant differences. At the end, 1.61x109 spores.mL-1 was obtained with IB15 and 6.46x108 spores.mL-1 with 2362. LT50 values were similar, being in average 2.5h in the experiments with one culture of the bacillus at the end of 24 hours. Strain IB15 showed to be suitable for growth in NYSM medium, presenting desirable levels of production of spores and toxins throughout fermentation. Further studies are needed on the large-scale production with that strain for the development of biolarvicides. Therefore, with the findings obtained in this study, one verifies the great importance of mosquito biological control with the use of entomopathogenic bacteria, showing to be a viable complement or alternative on the control of vector mosquitoes in Amazonia.