Chemical and Morphological Studies of Bacterial Spore Formation

The purine analogue, 8-azaguanine, was added to cultures of the parasporal crystal-forming organism Bacillus cereus var. alestl at different times during growth and synchronous sporulation. The effect of its incorporation has been studied with particular reference to cell growth, nucleic acid composition, cytology, and the synthesis of the spore and crystal protein. Additions of the analogue during any stage of growth prevented further cell proliferation and all spore and crystal formation. Since both nucleic acids continued to be formed, cells of an increased size developed, containing large masses of chromatin in the form of condensed balls or axial cords. Lipid-containing inclusions also appeared following these additions and were usually aggregated at the centre or poles of the cells. The analogue could be isolated as the ribonucleotide from both the acid soluble and RNA fractions of these inhibited cells. Additions of the analogue following commencement of sporulation did not prevent either spore or crystal formation or affect the nucleic acid content of the sporulating cells. However, as before, the 8-azaguanine was incorporated into both the acid soluble and RNA of the cells, but not into these fractions of the spores ultimately formed. The implications of these findings are discussed in relation to crystal protein synthesis.