Chapter XIII — 169 — The Phosphorus Cycle 



tion of sinking organic matter. Redfield's argument that some organic 

 matter must sink to depths as great as 600 to 800 meters is a commentary 

 on his belief that the vast majority of the organic matter must undergo 

 complete decomposition nearer the surface. 



Whether a specific bacterial flora is involved in the liberation of phos- 

 phate from phospholipids and phosphoprotcins or whether all lipolytic 

 and proteolytic bacteria are endowed with this ability is not known. 

 Special investigations are needed to answer this question, as well as to 

 elucidate the mechanism of phosphate regeneration. However, bacteria 

 which decompose organic compounds with the liberation of phosphate 

 appear to be abundantly and widely distributed in aquatic environments 

 as well as in soil. 



Unless properly preserved, there is nearly always an increase in the 

 phosphate content of either sea water or fresh water stored in the dark 

 (ZoBell and Brown, 1944). Waksman et al. (1937) have noted a rapid 

 regeneration of phosphate resulting from the bacterial decomposition of 

 diatoms. Waksman et al. (1938) made similar observations on decom- 

 posing copepods and other marine organic matter. 



Effect of bacteria on solubility of phosphate: — The solubility of 

 calcium phosphate in sea water is primarily a function of the ^H. The 

 solubility is increased as a result of the activities of bacteria which pro- 

 duce acidic substances and decreased by metabolites of alkaline character. 

 In localized microspheres where the phosphate content of the water is 

 relatively high, tricalcium phosphate may be precipitated from solution 

 owing to an increased pH caused by bacteria. 



The reverse process, namely the dissolution of tricalcium phosphate, 

 may be of considerable importance in the phosphorus cycle. It is of im- 

 portance on land where bacterial activities promote the mineralization of 

 rock phosphates. In the sea large quantities of phosphate are bound in 

 the bones of animals in the form of tricalcium phosphate. Part of the lat- 

 ter may be dissolved by the acidic digestive juices of carnivorous animals, 

 and part by bacteria and allied microorganisms. This they do in four dif- 

 ferent ways recorded in order of importance: (i) Generation of acids. 

 (2) Decomposition of organic matter associated with the bones, thereby 

 mechanically liberating some calcium phosphate, particularly from only 

 partially ossified tissue. (3) Production of ammonium salts and other 

 secondary reaction products which increase the solubility of tricalcium 

 phosphate. To the extent that it increases the pH, microbiologically pro- 

 duced ammonium may decrease the solubility of tricalcium phosphate, 

 but ammonium chloride and ammonium sulfate have a slight solvent 

 action. (4) Conversion of insoluble tricalcium phosphate into cell 

 phosphoprotcins or phospholipids by direct assimilation. 



Tricalcium phosphate, either in the form of bone or crystals, provides 

 an excellent surface for the attachment of marine bacteria and for the con- 

 centration of dissolved organic matter. This would promote increased 

 bacterial activity in the immediate vicinity of the tricalcium phosphate 

 where bacteria in microspheres may produce enough acid to have a solvent 

 action, though surrounded by shghtly alkaline water. 



