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

Abstract

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