Selective Process for Efficient Isolation of Soil Bacillus spp.

We were able to isolate Bacillus thuringiensis from environmental samples with a background of 10 bacteria per g of soil. Our selection process differed significantly from classical selection methods which permit only the desired organism to grow. In our process, germination of B. thuringiensis spores was selectively inhibited by sodium acetate, while most of the undesired sporeformers germinated. Next, all of the nonsporulated microbes were eliminated by heat treatment at 80 degrees C for 3 min. The surviving spores were then plated on a rich agar medium and allowed to grow until they sporulated. Of random colonies picked from agar, 20 to 96% were crystal-forming Bacillus species. B. thuringiensis and B. sphaericus were routinely selected by this method.