THE PHOSPHORUS FRACTIONS OF BACILLUS CEREUS AND BACILLUS MEGATERIUM: II. A CORRELATION OF THE CHEMICAL WITH THE CYTOLOGICAL CHANGES OCCURRING DURING SPORE GERMINATION

Abstract

The oxygen uptake, the changes in the concentrations of the phosphorus (P) fractions, and the dry weights of Bacillus cereus and B. megaterium germinating in thick suspension were followed from the spore to the young vegetative cell. Parallel cytological studies were made using standard procedures of bacterial cytology. During the initial minutes of germination the dry weight of the spores fell, respiratory activity began, the concentration of cold trichloroacetic acid (TCA)-soluble P rose, and the concentration of a residual P fraction insoluble in hot TCA fell. In complete media, nucleic acid synthesis began soon after this initial activation and was accompanied by an uptake of P, a further rise in the acid-soluble P, and in the rate of respiration. The cells began to recover weight. Ribosenucleic acid (RNA) synthesis was detectable by about 10 min. after inoculation and desoxyribosenucleic acid (DNA) synthesis by 15–20 min. Following its initial rise, the rate of RNA synthesis declined and continued parallel to that of DNA for some 10 min. During this period, the uptake of P from the medium appeared to be depressed and the spores (B. cereus) changed in shape from ovoids to short rods. After this period, the RNA synthesis was steady throughout germination. The rise of DNA, on the other hand, was continuous and steady throughout, even in cultures where growth was synchronous. The nuclear material of germinating spores grew and separated in step with the continuous rise of DNA P and the increase in cell volume was of the same order as the increase in RNA P. Under crowded conditions, or in inadequate media, germinating spores and young vegetative cells of B. cereus showed a decreased RNA/DNA ratio and accumulations of labile P. Crowded cultures of B. megaterium, on the other hand, accumulated Sudan positive (fatty) granules, but no labile P. The time required for the germinating spore to duplicate its chromatin varied in different media and could, in some instances, be shortened by subculturing. Nevertheless, the product of this time of germination and the increase in RNA during the germination period approximated to a fixed value that was independent of medium, species, or cell concentration.