Adhesion and cytotoxicity of Bacillus thuringiensis to cultured Spodoptera and Drosophila cells.

Two Bacillus thuringiensis strains were tested for the ability to adhere to cultured Spodoptera and Drosophila insect cells. The wild-type strain is virulent and motile and readily adheres to and kills both types of insect cells. The avirulent mutant strain, which lacks flagella and several other of the proposed virulence factors, does not adhere to the insect cells and does not kill these cells efficiently. Purified flagella bind to insect cells; addition of anti-flagella serum abolishes cell binding and reduces the killing efficiency. Both bacteria and culture supernatant from the wild-type strain, but not from the mutant, are cytotoxic. Of the factors known to be reduced in the avirulent mutant, such as flagellin and phosphatidylcholine (PC) degrading or phosphatidylinositol-specific phospholipase C (PLC), only PC-PLC is shown to be cytotoxic.