Bacteria are found in the sea which are capable of utilizing petroleum ether, gasoline, kerosene, lubricating oils, crude oils, petrolatum, paraffine wax, mineral oil, methane, pentane, hexane, decane, trimethylpentane, tetratriacontane, benzene, xylene, toluene, cyclohexane, anthracene, naphthalene, and other hydrocarbons. Sea water from the euphotic zone contains 10 to 1,000 hydrocarbon-oxidizing bacteria per liter, and 100 to 100,000 such bacteria have been found per gram of recent marine sediments. All samples of sediments regardless of distance from land, water depth, or core depth have shown the presence of hydrocarbon-oxidizing bacteria. Most of the bacteria oxidize hydrocarbons only in the presence of free oxygen although some of them can utilize nitrate as a hydr gen acceptor. Possibly some of them can activate sulphate as a hydrogen acceptor. Hydrogen sulphide in concentrations exceeding 0.0001 mol per liter inhibits the bacterial oxidation of petroleum hydrocarbons.

Within certain limits long-chain hydrocarbons are oxidized more readily than those of smaller molecular weight, and aliphatic compounds are more susceptible to bacterial oxidation than cyclic or aromatic hydrocarbons. Compounds with unsaturated bonds are attacked more readily than saturated compounds. Carbon dioxide, methane, organic acids, and bacterial protoplasm are among the products resulting from the bacterial utilization of petroleum hydrocarbons. Species of Proactinomyces, Actinomyces, Pseudomonas, Micromonospora, Mycobacterium, and possibly other genera of marine microorganisms are able to oxidize hydrocarbons.

Although the reaction will take place in an aqueous system, the presence of sand, silt, diatomaceous earth, and other inert adsorbents accelerates the bacterial oxidation of hydrocarbons. Samples of crude oil added to marine sediments are rapidly destroyed under aerobic conditions. The activity of hydrocarbon-oxidizing bacteria, which appear to be widespread in occurrence, may account for the failure of certain workers to find petroleum hydrocarbons in sediment samples. Similarly such bacteria might prevent the accumulation of detectable quantities of hydrocarbons in experiments with mixed cultures designed to demonstrate the transformation of organic matter into hydrocarbons. Our work suggests that one might expect to find oil accumulating in recent sediments or in experimental mater al only if conditions are inimical to the activity of hydrocarbon-oxidizing bacteria.