Formation of the Parasporal Inclusion of Bacillus thuringiensis

Under given experimental conditions, a reproducible sequence of biochemical events can be measured during sporulation in Bacillus thuringiensis . Electron microscope studies reveal that, during its formation, the crystalline inclusion of Bacillus thuringiensis is closely associated with the exosporium. This association persists through several serial sections and can also be demonstrated in a mutant strain which is biochemically blocked soon after crystal formation. Two asporogenic crystalliferous strains produce a toxin active on larvae of Plutella maculipennis whereas two sporogenic, acrystalliferous strains are not toxic. Data from immunological assays and from pulse‐chase and label‐chase experiments with [ 14 C]leucine indicate that the crystal protein is synthesized at the time of appearance of crystal antigens. It is suggested that the crystal is synthesized and assembled on the exosporium.