Worldwide Abundance and Distribution of Bacillus thuringiensis Isolates.

We found the insect control agent Bacillus thuringiensis to be a ubiquitous soil microorganism. Using acetate selection to screen soil samples, we isolated B. thuringiensis in 785 of 1,115 soil samples. These samples were obtained in the United States and 29 other countries. A total of 48% of the B. thuringiensis isolates (8,916 isolates) fit the biochemical description of known varieties, while 52% represented undescribed B. thuringiensis types. Over 60% (1,052 isolates) of the isolates tested for toxicity were toxic to insects in the orders Lepidoptera or Diptera. Soil samples were collected from various habitats, including those habitats with different numbers of insects. The current presence of insects did not predict the presence of B. thuringiensis in a particular soil sample. B. thuringiensis was most abundant in samples from Asia.