Update on the detection of beta-exotoxin in Bacillus thuringiensis strainsby HPLC analysis

Aims: The current work aimed to study the presence of beta -exotoxin by hig h-performance liquid chromatography (HPLC) in supernatant fluids from final whole cultures of the 69 type strains and 13 subtypes of Bacillus thuringi ensis strains, as well as from some insecticidal strains. Methods and Results: Results from HPLC and bioassays with Ephestia kuhniell a (Lepidoptera Pyralidae) were compared. Type I beta -exotoxin was only det ected in type strains representing serotypes H1, H9 and H10a,10b. Discrepan cies between HPLC and bioassays were found in H8a,8b and some insecticidal strains, which suggests the occurrence of another soluble toxin different f rom type I beta -exotoxin, possibly type II beta -exotoxin. Conclusions: This study shows the need to use bioassays to determine the pr esence of beta -exotoxin activity. However, HPLC is a fast and sensitive te chnique if only type I beta -exotoxin is to be determined. The occurrence o f beta -exotoxin in a type strain does not imply production of this metabol ite by other strains belonging to the same serovar. Significance and Impact of the Study: These results complete the characteri zation of type strains belonging to the International Entomopathogenic Baci llus Collection (Institut Pasteur, Paris, France).