Microbial Products and Soil Organic Matter: I. Some Characteristics of the Organic Phosphorus of Microorganisms

THE phosphorus content of microorganisms is relatively high and its distribution among the several organic, phosphorus-carrying compounds is quite different from that found in higher plant tissues and in many animal tissues. Microorganisms normally contain about 2.0 to 5.0% phosphorus (dry wt. basis) (6). This is much'higher than is found in plants (0.05 to 0.35%). For convenience of study the phosphorus bearing compounds in most tissue have been grouped into four general categories. These are the acid soluble, the phospholipid, the nucleic acid, and the phosphoprotein groups. The properties of the compounds in each group are much alike in all types of tissue. The relative proportion of the phosphorus occurring in each phosphorus carrying group, however, varies markedly among, and to a certain extent within, the plant, animal, and microbial kingdoms. The acid soluble group is separated from the other groups by use of dilute trichloracetic acid in the cold. It contains soluble inorganic phosphorus and most of the phosphorus-carrying products and agents of intermediate metabolism such as hexose and triose phosphates, adenosine phosphates, phosphopyruvic acid, and coenzymes. Phytin has not been positively identified as a component of microbial tissue. If present, it should be a part of the acid soluble group. The phospholipid fraction is separated by treatment of the cells with hot fat solvents, commonly ethyl alcohol, ethyl ether, and chloroform. Little is known of the chemical nature of microbial lipids. Perhaps the most extensive study has been made on the tubercle bacillus, an organism which is high in lipids (1). The relative quantity of phospholipid material in cell tissue varies markedly among the many microbial groups. Two general types of nucleic acid have been recognized and studied. Both types are common to plants, animals, and microorganisms. It is generally agreed among investigators (2) that the one type, ribonucleic acid, is the normal constituent of the cytoplasm, whereas, the second type, desoxyribonucleic acid, is the normal constituent of the nucleus. Although both types have many properties in common, they differ structurally in their pentose components, in one of the nucleotides, and in the positions of linkage of the nucleotide by the phosphoryl .groups (4). They differ also in the ease and conditions of fragmentation and hydrolysis (7). The latter differences constitute one basis for separation and quantitative determination. Phosphoprotein is one of the minor phosphorus bearing constituents in microorganisms and seldom constitutes more than a few percent of the total organic phosphorus. Phosphoproteins may be separated and quantitatively determined on the basis of differential conditions of solution and dephosphorylation. The data presented in this report show the quantitative distribution among the foregoing groups of the organic phosphorus of Aerobacter aerogenes cells, the relative rates of dephosphorylation accompanying disintegration and decomposition of the cells, and the influence of bentonite on the apparent phosphorus distribution and subsequent dephosphorylation.