Release of Bacillus thuringiensis subsp. israelensis in Swedish Soil

A streptomycin-resistant strain of Bacillus thuringiensis subsp. israelensis (BtN14) was released in a field experiment and the effect on the indigenous bacterial flora was analyzed. A minor, transient increase of the concentration of B. thuringiensis/cereus-like bacteria was detected. The released strain was able to establish itself at a low number, but the total concentration of B. thuringiensis subsp. israelensis was not affected. BtN14 was detected outside the release site, but decreased to a concentration below the detection limit (20 cfu g−1 soil) at the end of the test period. Laboratory experiments showed that the released strain can grow in non-sterilized as well as sterilized soil, but that growth was very slow and transient in non-sterilized soil. Seven weeks after release, no remaining effects on the total bacterial population could be detected.