Characterization and pathogenic evaluation of Bacillus thuringiensis and Bacillus sphaericus isolates from Argentinean soils

Eighty soil samples of different origin (from urban, agricultural, forested and horticultural areas) which had not previously been treated with bioins ecticides, were collected and examined to investigate the presence of Bacil lus thuringiensis and B. sphaericus. From a total of 1473 bacterial isolate s examined by differential staining techniques and growth on nutrient agar with the addition of penicillin and streptomycin, 31 (2.1%) strains of Baci llus sphaericus and 25 (1.6%) strains of Bacillus thuringiensis were isolat ed. These strains were tested for their pathogenicity against Diptera (Cule x quinquefasciatus) and Lepidoptera (Anticarsia gemmatalis and Spodoptera f rugiperda). Seven strains of Bacillus thuringiensis subspecies kurstaki wer e found to be pathogenic to Spodoptera frugiperda and twenty-two strains sh owed a pathological effect against Anticarsia gemmatalis. None of the strai ns of Bacillus thuringiensis nor the Bacillus sphaericus investigated, show ed pathogenic activity against Culex quinquefasciatus. The strains of Bacil lus thuringiensis were characterized serologically as belonging to six sero types (darmstadiensis, entomocidus, kurstaki, muju, sotto and xianguangiens is). One strain seemed to be a new serotype. The electrophoretic profiles o f the strains of Bacillus thruringiensis showed bands of 130 kDa similar to those found in strains pathogenic against Lepidoptera. Some physicochemica l characteristics were also studied in the soil samples, in order to relate them to the presence or absence of these Bacillus species.