RESUMO
Bacillus thuringiensis was isolated from 36 of 50 residue samples obtained from an animal feed mill (a stored-product environment). Of 710 selected colonies having Bacillus cereus-B. thuringiensis morphology isolated from the samples, 477 were classified as B. thuringiensis because of production of parasporal delta-endotoxin crystals. There was a diverse population of B. thuringiensis, as revealed by differentiation of the isolates into 36 subgroups by using (i) their spectra of toxicity to the lepidopterans Heliothis virescens, Pieris brassicae, and Spodoptera littoralis and the dipteran Aedes aegypti and (ii) their parasporal crystal morphology. A total of 55% of the isolates were not toxic to any of these insects at the concentrations used in the bioassays; 40% of all isolates were toxic to one or more of the Lepidoptera; and 20, 1, and 1% of the isolates were toxic to only P. brassicae, H. virescens, and S. littoralis, respectively. The most frequent toxicity was toxicity to P. brassicae (36% of all isolates); 18% of the isolates were toxic to A. aegypti (5% exclusively), 10% were toxic to H. virescens, and 4% were toxic to S. littoralis. Toxicity to P. brassicae was more often linked with toxicity to H. virescens than with toxicity to S. littoralis. The frequency of toxicity was significantly greater in isolates that produced bipyramidal crystals than in isolates that produced irregular pointed, irregular spherical, rectangular, or spherical crystals.
RESUMO
This study describes the isolation of a phage, using mitomycin C and u.v. light, from each of four strains (HD67, HD130, HD228 and HD248) of Bacillus thuringiensis H-serotype 7 (var. aizawai). It also describes the isolation of two indicator strains (12.13 and HD102) for these phages (phi HD67, phi HD130, phi HD228 and phi HD248) and the ideal conditions, using these indicator strains, for maximum phage production.
