Chapter X — 145 — Organic Matter 



genera. Most of the strains of Microtnonospora isolated from lake mud by 

 Erikson (1941) readily decomposed chitin. 



Chitin is attacked more slowly than most other common types of 

 organic matter. It is decomposed less readily anaerobically than aero- 

 bically. In spite of the widespread distribution of chitinoclastic bacteria 

 in the sea, chitin persists as one of the principal nitrogenous constituents 

 of marine sediments (Hecht, 1934; Waksman, 1933). 



Lipolytic bacteria : — Fats and oils of varying degrees of complexity 

 are synthesized as part of the cell substance by most bacteria, yeasts, and 

 molds. However, the amount synthesized is insignificant as compared 

 with the amount which they decompose. The following mean values 

 given by Trask (1939) show the lipid content of the organic matter of 

 sediments and that of the principal groups of organisms living in the water : 



Ether Crude Carbohy- 



The ether extract includes oils, fats, certain pigments, sterols, and waxes. 

 Further examination has revealed that not only is there a great decrease 

 in the ether-extract content of organic matter deposited on the sea floor, 

 but that fats and oils decrease proportionately faster than waxes. 



It is difficult to assess the relative importance of animals and bacteria 

 in the decomposition of fats and oils, but it is known that lipolytic bac- 

 teria are widely distributed in the sea. Nearly all types of fats and oils 

 seem to be attacked by bacteria in sea water and marine mud. Certain 

 pure cultures, notably anaerobes, hydrolyze tripalmitin, tristearin, and 

 other pure fats with the liberation of fatty acids. Presumably the glycerol 

 which results from the hydrolysis of triglycerides is oxidized as a source of 

 energy. 



Some lipolytic bacteria utilize fatty acids under certain conditions. 

 Whether the fatty acids are utilized or left apparently depends partly 

 upon the organisms involved and partly upon the environmental or nu- 

 tritional conditions. The hydrolysis of fats and the transformation of 

 fatty acids are believed to be of considerable importance in the origin of 

 petroleum. From the formulae of fatty acids, it is evident that the de- 

 oxygenation or decarboxylation of fatty acids may result in the formation 

 of petroleum hydrocarbons: 



CH3(CH2)„CH.2COOH = CH3(CH2)nCH3 + CO. 



Relationships of microorganisms to the generation of petroleum with 

 particular reference to fats and oils are reviewed by Hammar (1934). 

 In his doctorate dissertation work at the S.I.O., which is concerned 

 with the transformation of lipids by marine anaerobes, W. D. Rosenfeld 

 has found lipoclastic anaerobes to be widely and abundantly distributed 

 in recent marine sediments, oil-well brines, tar sands, asphalt deposits, 

 and in paraffin earth samples. Fatty acids are not readily oxidized under 

 anaerobic conditions in the absence of glycerol, an observation which sug- 

 gests that there is a concomitant oxidation of glycerol and reduction of 

 fatty acid. Binary combinations of fatty acids appear to be assimilated 



