Serological identification and insect toxicity of Bacillus thuringiensis isolated from the island Okinoerabu-jima, Japan

We examined soils of the island Okinoerabu-jima, Kagoshima Prefecture, Japan, for the occurrence of Bacillus thuringiensis. The organism occurred in 13 (65%) out of 20 soil-sampling sites, and 27 (27%) out of 100 soil samples. Among 2,680 Bacillus cereus group colonies examined, 66 were allocated to B. thuringiensis. Soils of the island provided at least 11 H-serotypes. Most of the isolates exhibited no insecticidal activities, while an isolate of serovar kurstaki (H3abc) with bipyramidal parasporal inclusions killed both dipteran and lepidopteran larvae, and another isolate of serovar colmeri (H21) with irregularly-pointed inclusions had a high mosquitocidal activity. None of the seven isolates of serovar israelensis (H14) showed mosquito larvicidal activities, while producing parasporal inclusions morphologically similar to those of the reference strain of serovar israelensis with strong mosquitocidal activities.