Isolation and characterization of a Bacillus thurigiensis strain with potential for epizootics in Plodia interpunctella

Bacillus thuringiensis is a Gram-positive bacterium known for its insecticidal activity against various insect species, making it an excellent biocontrol agent. Although B. thuringiensis is regarded as an opportunistic entomopathogen due to the naturally low incidence of epizootics, certain strains, such as B. thuringiensis serovar aizawaii, have shown the potential to induce epizootics in Plodia interpunctella (Lepidoptera: Pyralidae). In this study, we isolated the strain INTA L404-1 from the hemolymph of a dead P. interpunctella larva collected from artificial rearing at CEPAVE (La Plata, Argentina), where a high mortality rate was observed. DNA was extracted from the purified bacterium using a commercial kit, and Illumina sequencing was performed for strain identification. Nine insecticidal protein genes were identified, including cry1Aa, cry1Ab, cry1Ca, cry1Da, cry1Ia, cry2Ab, cry9Ea, spp1Aa, and vip3Aa, with amino acid sequence identities ranging from 80% to 100%. Additionally, the proteins from the genes, similar to cry9Ec, mpp3Aa, and tpp80Aa, exhibited sequence identities below 34%. These results suggest the potential of INTA L404-1 as a biocontrol agent. Bipyramidal crystals were observed in INTA L404-1, and an SDS-PAGE analysis of parasporal crystals revealed a unique ca. 130 kDa protein. This strain demonstrated significant insecticidal activity, causing 100% mortality in Cydia pomonella (Lepidoptera: Tortricidae) when incorporated into the larvae's diet. B. thuringiensis INTA L404-1 may induce epizootics in the artificial rearing of P. interpunctella, as evidenced by the observed spread of infection among pest offspring. To confirm this, it is necessary to assess the strain INTA L404-1 in bioassays with P. interpunctella to demonstrate that it causes mortality like that observed in the original host. The insecticidal protein gene profile of INTA L404-1 is comparable to that of other B. thuringiensis serovar aizawaii strains.