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 O2-uptake, the changes in concentrations of the 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 weights of the spores fall, respiratory activity begins, the concentration of cold trichloro-acetic acid (TCA)-soluble P rises, and the concentration of a residual P fraction insoluble in hot TCA falls. In complete media, nucleic acid synthesis begins soon after this initial activation and is accompanied by an uptake of P, a further rise in the acid-soluble P and in the rate of respiration. The cells recover weight. Ribosenucleic acid (RNA) synthesis is detectable about 10 minutes after inoculation and desoxyribosenucleic acid (DNA) synthesis by 15-20 minutes. Following its initial rise, the rate of RNA synthesis declines and continues parallel to that of DNA for some 10 minutes. During this period, the uptake of P from the medium appears to be depressed and the spores (B. cereus) change in shape from ovoids to short rods. After this period, RNA synthesis is steady throughout germination. The rise of DNA, on the other hand, is continuous and steady throughout, even in cultures where growth is synchronous. The nuclear material of germinating spores grow and separate in step with the continuous rise of DNA P and the increase in cell volume is 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 show a decreased RNA/DNA ratio and accumulations of labile P. Crowded cultures of B. megaterium, on the other hand, accumulate Sudan-positive (fatty) granules, but no labile P. The time required for the germinating spore to duplicate its chromatin varies in different media and can, in some instances, be shortened by subculturing. Nevertheless, the product of this time of germinating and the increase in RNA during the germination period approximates a fixed value that is independent of medium, spp., or cell concentration.