Protein turnover and the formation of protein inclusions during sporulation of Bacillus thuringiensis.

During sporulation of Bacillus thuringiensiS, a spore and a protein parasporal inclusion are formed within each cell (Hannay & Fitz-James, 1955; Hannay, 1956). The parasporal inclusions are of a regular, dipyramidal form and are referred to as 'crystals'. Similar 'crystals' are formed by a number of related strains of Bacillus, all of which are pathogenic to insect larvae. The crystals are composed of protein, and contain no nucleic acid or carbohydrate. The crystals are insoluble in water and do not disperse until the pH is raised to a value above 11-8. After such dispersal, the crystal protein remains in solution over a range of pH values from 6 upwards. It has been shown (Monro, 1961) that normal sporulation with concomitant formation of protein crystals can take place during incubation under suitable conditions in a nutrient-free medium. It has further been shown that crystal protein antigens are absent from vegetative cells and arise over the same period as the crystals during sporulation. It is thus clear that the crystal protein must be derived from material already present in the cells before sporulation but that such precursor material is antigenically unrelated. In the present paper, chemical analysis and tracer techniques have been employed to investigate whether crystals are formed through modification of antigenically unrelated protein or polypeptide components, or whether proteins break down during sporulation, supplying amino acids for synthesis of the crystal protein. With the aid of a serological method, which has been developed for the rapid, reproducible separation of the crystal protein, it has been found that the crystal protein is synthesized from amino acids during sporulation, and that a process of protein turnover takes place. These results are in agreement with related observations of Young & Fitz-James (1959), who have shown by somewhat similar techniques that the crystal protein of a related strain is synthesized during sporulation. Further studies show that a general process of protein turnover occurs during sporulation under the conditions employed and that, as well as the