THE PHOSPHORUS FRACTIONS OF BACILLUS CEREUS AND BACILLUS MEGATERIUM: I. A COMPARISON OF SPORES AND VEGETATIVE CELLS

Abstract

The P fractions of spores and young vegetative cells of B. cereus and B. megaterium were compared. Differences were found, not only between the 2 types of cell, but also between the spp. studied. The spores of B. cereus and B. megaterium contain, on a dry weight basis, similar amounts of nucleic acid, yet the spores of B. megaterium contain twice as much total P as those of B. cereus. The excess P of B. megaterium spores is present as an acid- and alkali-insoluble residue and is made up of empty spore coats. While this same fraction accounts for only 4% of the total P of B. cereus spores, it makes up some 60% of that of B. megaterium. A similar fraction from vegetative cells is low in P. The spore coats of B. megaterium, in contrast to the cell walls, are lysozyme-resistant. Cold acid-soluble and lipid P can be estimated properly only on disrupted spores. Disruption is essential for the ready extraction of spore nucleic acids with hot trichloracetic acid (TCA), but does not alter greatly the solubility of the residue P. Ribosenucleic acid (RNA) comprises 50% of the total P in the spores of B. cereus (3-4% of the dry weight, but only 25% in B. megaterium spores. In both spp., the RNA of the vegetative forms accounts for a larger proportion of the total P of the cell. Ribonuclease digests the RNA of spores and vegetative cells to the same degree. The Schmidt and Thannhauser method is more suitable than the Schneider method for the estimation of desoxyribosenucleic acid (DNA). The DNA content of B. cereus spores is about 1% of their dry weight; that of B. megaterium spores is slightly less. Some 12-20% of the P of B. cereus spores and 6% of that of the young vegetative cells is present as acid-labile (non-nucleic acid) P which exhibits some of the characteristics of polymetaphosphate.