Journal of Applied Microbiology, Vol.93, No.2, 269-277, 2002
Combined analysis of supernatant-based feeding bioassays and PCR as a first-tier screening strategy for Vip-derived activities in Bacillus thuringiensis strains effective against tropical fall armyworm
Aims: To assess whether feeding bioassays using culture-supernatant proteins could be combined with PCR into a first-tier screening strategy for Vip3A -like genes efficient against tropical Spodoptera frugiperda . Methods and Results: Out of 12 Bacillus thuringiensis strains studied, the total protein concentrated from the culture supernatant of only the strain HD125 yielded a significantly increased armyworm mortality and an intense band of the predicted size for VIP3A protein in SDS-PAGE. However, PCR and sequencing data indicated Vip -like genes are ubiquitous in tropical B. thuringiensis isolates. Interestingly, the HD125 strain was also the only one displaying a single-band amplification pattern and the highest sequence identity to the reported Vip3A(a) gene. Conclusions: Results suggest the insecticidal effectiveness of putative VIPs in B. thuringiensis isolates can be preliminarily estimated by the use of supernatant-derived total protein in feeding experiments, though only in a limited manner. Significance and Impact of the Study: A simple and cost-effective first-tier screening strategy for VIP-derived activities in B. thuringiensis collections can be developed by combining PCR and feeding bioassays. Moreover, the employed primers showed to be useful as a tool for strains differentiation at DNA level, and for characterization and isolation of Vip -like genes in tropical B. thuringiensis germplasm.