Persistence of Toxic Activity of Fermentation Extracts fromBacillus thuringiensisvar.israelensisafter More Than Three Decades of Storage

Abstract

This study was carried out to determine the persistence of toxicity of fermentation extracts of Bacillus thuringiensis var. israelensis after more than three decades of storage. For this purpose, a population of Aedes aegypti was established. The mortality rate of 20 spore-crystal extracts purified using the acetone-lactose coprecipitation method was measured and evaluated by bioassays according to a modified WHO protocol. The extracts with the highest mortality rate were determined in triplicate by their LD50 and LD98. All extracts showed toxicity at the highest tested dose (1000 ppm) and some, such as strains 3260 and 3501, still killed larvae at doses as low as 0.01 ppm. These data are surprising because no study on the activity of B. thuringiensis toxic proteins after such a long storage time has been reported.

In vitro assessment of the Larvicidal activity of Bacillus thuringiensis israelensis (Vectobac 12AS formulation) on Anopheles mosquito larvae

“…On the other hand, a low level of larval mortalities was observed in all the treatments as the concentrations of Vectobac 12AS decreases. This finding is in agreement with the findings of previous research [28] who also reported that most of these Bacillus thuringiensis israelensis extracts showed some toxic activity toward mosquito larvae in high concentrations, but their activity decreased as the dilution increased. This could be attributed to the fact that, much higher concentrations of Bti formulation are required in order to induce mortality in Anopheline larvae than in any other larval mosquito specie.…”

Toxic Potential ofBacillus thuringiensis: An Overview

“…Twenty samples of the strain HD-500 and HD-567 of Bti fermentation extracts from the collection of Dulmage et al [44] recovered by lactose-acetone coprecipitation during the period from 1978 to 1983 maintained their residual toxic activity against the mosquito Aedes aegypti. All extracts evaluated presented toxicity at the highest tested doses (1000 ppm), and two of the stored extracts (3260 and 3501) showed LD50 of 0.12 and 1.16 ppm, respectively [40].…”

“…Dulmage sets up the basis for the fermentation and formulation procedures of Bt culture extracts for their commercialization [39] and were among the most important pioneers in the development of technologies for the implementation of Bt as a biological pest control agent. He established diverse methodologies for mass production product formulation and power standardization [40].…”

Viability and reconstitution of delta-endotoxins from Bacillus thuringiensis var. israelensis extracts after forty years of storage against Aedes aegypti (Diptera: Culicidae)

“…Five Bti fermentation extracts with the code: 3260, 3501, 3691, 3696, and 3756, respectively, were produced by coprecipitation lactose-acetone method by Dulmage et al (1970) at the US Department of Agriculture, Agricultural Research Service (USDA-ARS) from the strains HD-500 and HD-567, chosen from the previous work of Galán et al (2017). During the storage period, all extracts were stored in dark and dry conditions exclusively for this purpose at 25 ± 3°C in sterile and hermetic bottles.…”

“…A recent study was undertaken to evaluate the persistence of 20 Bti extracts stored for prolonged periods of time. All extracts presented biological activity at high concentrations against A. aegypti larvae, demonstrating the biological persistence of crystal proteins (Galán et al 2017). The reconstitution and characterization of Bti toxins has never been evaluated after long storage periods, nor observed whether they have retained their genetic capacity and maintained the same biologic activity after reactivation.…”