Chapter X — 147 — Organic Matter 



Many if not all plants including bacteria synthesize waxes and allied 

 hydrocarbons to some extent. Baas Becking et al. (1927) found that 9.7 

 per cent of the organic matter of diatoms, mostly Aulacodiscus kitloni, was 

 extractable by ether, and that 65.7 per cent of the ether extract was un- 

 saponiiiable. The unsaponiliable material consisted of hydrocarbons, 

 with lesser amounts of phytosterol and related alcohols. Trask (1939) 

 reports 8 per cent as the average ether-extractive content of the organic 

 matter in marine diatoms. 



Clarke and Mazur (1941) found that from 3 to 14 per cent of the 

 ether extractives of marine diatoms consisted of hydrocarbons, part of 

 which was identilied as hentriacontane, C31H64. After six months incuba- 

 tion in the presence of mud-dwelling microorganisms there was a marked 

 decrease in the organic acid content of diatoms and an increase in hydro- 

 carbons. Hentriacontane occurs commonly in plant tissues, often in con- 

 siderable abundance as in the candelilla plant, Euphorbia cerifera, for ex- 

 ample. Literature on the occurrence of hydrocarbons in the tissues of 

 terrestrial plants has been reviewed by Sever (1933), Chibnall et al. 

 (1934), and Sanders (1937). Hydrocarbons also occur in animal tissues, 

 Squalene, CsoHbo, found in large amounts in the livers of sharks, is a no- 

 table example. 



In certain environments unfavorable for the activity of hydrocarbon- 

 oxidizing bacteria, hydrocarbons may accumulate in bottom deposits, but 

 under other environmental conditions bacteria may oxidize hydrocar- 

 bons. According to ZoBell et al. (1943), species of Actinomyces, Micro- 

 monospora, Mycobacterium, Pseudomonas, and other genera, which attack 

 aliphatic, aromatic, naphthenic, and oleiinic hydrocarbons in the presence 

 of free oxygen, are widely distributed in sea water and marine mud. In 

 general, long-chain hydrocarbons are attacked more readily than those of 

 lower molecular weight, and aliphatic compounds are more susceptible to 

 bacterial oxidation than are cyclic or aromatic compounds. Open-chain 

 hydrocarbons having unsaturated bonds are attacked more readily than 

 corresponding saturated compounds. Side-chains appear to be attacked 

 preferentially. CO2, organic acids, bacterial protoplasm, and methane 

 result from the action of bacteria upon complex hydrocarbons. There is 

 some evidence that higher hydrocarbons are converted into simpler homo- 

 logues besides methane. 



Anaerobic sulfate reducers found by Tausson and Alioschina (1932) 

 in lakes, rivers, limans, and the sea were able to utilize saturated aliphatic 

 hydrocarbons containing ten or more carbon atoms per molecule. Naph- 

 thenic hydrocarbons were not attacked by sulfate reducers. Upon a basis 

 of thermodynamic considerations, these workers concluded that heavy 

 hydrocarbons may be converted into polymethylene compounds by sul- 

 fate reducers. 



Desidfovibrio species of marine origin attack waxes and heavy oils with 

 the formation of lighter hydrocarbons, according to Novelli and ZoBell 

 (1944). Neither aliphatic hydrocarbons simpler than decane nor aro- 

 matic compounds were attacked. Decane was slowly utilized as a sole 

 source of carbon. Tetradecane, cetane, and longer molecules were at- 

 tacked anaerobically, progressively more readily as the chain length of the 

 hydrocarbon increased. 



Micromonospora species isolated from Lake Mendota mud by Erikson 

 (1941) rapidly oxidized paraffin wax, paraffin oil, toluene, naphthalene, 

 benzene, phenol, resorcinol, m-cresol, and /3-naphthol. From sediments 



