652 PRINCIPLES OF SOIL MICROBIOLOGY 



In addition to these compounds, other organic phosphorus com- 

 pounds, such as that of wheat bran (inosite mono-phosphate — CeH^OgP) 

 are added to the soil, in considerable quantities. Their decomposition 

 is probably similar to that of phytin. 



Transformation of insoluble tri-calcium phosphates into soluble forms 

 by microorganisms. Insoluble tri-calcium phosphates may be brought 

 into solution by microorganisms in three different ways: (1) by the 

 direct metabolism of microorganisms, perhaps through the formation 

 of some enzyme or interaction with some synthesized substance, (2) by 

 the action of carbon dioxide as well as various organic acids produced 

 by soil microorganisms, (3) by the action of inorganic acids formed in 

 the metabolism of the autotrophic nitrifying and sulfur oxidizing 

 bacteria. 



Soil microorganisms were found capable of rendering insoluble tri- 

 calcium phosphate soluble when it is present in culture media as the 

 only source of phosphorus. Attempts have been made to explain this 

 by a direct metabolism of the organism, involving the formation of 

 specific enzymes. It has also been suggested 25 that various fungi may 

 directly assimilate the phosphorus from the tri-calcium phosphate: Asp. 

 niger, Pen. brevicaule, Pen. glaucum assimilated, in 60 days at 22°C, 

 one-fifth to one-third of the phosphate present as Ca 3 (P0 4 )2 in liquid 

 culture media. When the mycelium of the organisms is further de- 

 composed by soil bacteria and fungi, the phosphorus goes into solution 

 in an available form. 



Out of twenty-five bacteria isolated from the soil, twelve had a defi- 

 nite solvent action on rock phosphate, bone, pure tri-calcium phos- 

 phate, di-calcium phosphate and calcium carbonate, when supplied 

 with some form of sugar in the nutrient medium. 26 Both the acid 

 formed by the bacteria and the carbon dioxide were found to be factors 

 exerting the solvent action. The solubility of phosphates is influenced 

 by the nature of carbon and nitrogen sources for the growth of micro- 

 organisms; 27 disaccharides are better sources of carbon than mono- 



26 de Grazia, S., Gerza, U. Sull intervento dei microorganismi nella utiliz- 

 zazione dei fosfati insolubili del suolo da parte delle piante superiori. Ann. 

 R. Sta. Chem. Agr. Sper. Roma (II), 2. 1908; 3. 1909. 



26 Sackett, W. G., Patten, A. J., and Brown, C. W. The solvent action of 

 soil bacteria upon the insoluble phosphates of raw bone meal and natural raw 

 rook phosphate. Centrbl. Bakt. II, 20: 688-703. 1908. 



27 Perotti, R. tlber den biochemischen Kreislauf der Phosphosiiure im Acker- 

 boden. Centrbl. Bakt. II, 25: 409-419. 1909. 



