Abstract
The objective of this work was to select the most active Bacillus thuringiensis (Bt) isolated from agricultural soils of Mali through the molecular characterization and the determination of insecticidal activities of the protein crystals, produced by these native isolates. Crystal proteins were extracted from B. thuringiensis culture, and characterized using the SDS-PAGE techniques. Their insecticidal activities were tested using third-instar larvae of Helicoverpa armigera in bioassay tests. The results showed that, of 62 B. thuringiensis treated, 52 isolates showed fragments varying between 10 and 140 kDa on 12% polyacrylamide gel. Cry1 and Cry2 protein crystals were recognized to be effective against Lepidoptera’s larvae, which were found in 21% of the tested isolates. In addition to these two expected crystal protein weights, other molecular weights were observed at different proportions, suggesting the presence of other cry genes in the local B. thuringiensis isolates. Four native B. thuringiensis isolates were able to kill 95 to 100% of H. armigera 3rd-instar larvae. Only one native of B. thuringiensis isolate was able to kill 100% of the H. armigera larvae. This is the first study for molecular characterization of Malian native B. thuringiensis isolates, showing the efficacy of the native B. thuringiensis against an important agricultural insect pest. Key words: Protein crystals, Bacillus thuringiensis, cry genes, insecticidal activity, molecular characterization, Helicoverpa armigera, Mali.
Highlights
The introduction and subsequent proliferation of synthetic insecticides has played a key role in increasing agricultural productivity, protecting forest crops, and controlling insect vectors of human diseases (Joung and Côté, 2000)
Profile and frequency of Cry proteins synthetized by the native B. thuringiensis isolates
To determine the ability of the Malian B. thuringiensis (Bt) isolates to synthetize Cry proteins, the 62 isolates were characterized by SDS-PAGE
Summary
The introduction and subsequent proliferation of synthetic insecticides has played a key role in increasing agricultural productivity, protecting forest crops, and controlling insect vectors of human diseases (Joung and Côté, 2000). B. thuringiensis is a sporoform ubiquitous gram-positive bacterium that forms protein crystals (protoxins) during the stationary phase of its growth cycle (Schnepf et al, 1998). These protein exhibit toxious activities against insect larvae (Nazarian et al, 2009; Pardo-Lopéz et al, 2013). B. thuringiensis toxins are specific to a limited number of insect species without any toxicity to humans or other organisms (Bravo et al, 2011). Some of them are toxic to a large number of insect species in this order; Lepidoptera, Diptera and Coleoptera in addition to some Homoptera (MacIntosh et al, 1990; Bravo et al, 2007; Porcar et al, 2009; Palma et al, 2014), and Nematodes (Wei et al, 2003)
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