Bacterial Oxidation of Hydrocarbons in Marine Sediments. ∗

It has been demonstrated 1 that certain bacteria, widely distributed in nature, are capable of utilizing petroleum hydrocarbons as a source of energy. Recently Grant and ZoBell 2 have demonstrated the presence of such bacteria in marine environments.

If such bacteria are active in marine sediments, in situ, they may account for the dearth of hydrocarbons 3 in this material; thereby influencing the present theories of petroleum genesis. Therefore studies were undertaken to obtain more information on factors which may influence the activity of these bacteria in potential source-sediments.

Experimental. The sediments used in this investigation were samples of bottom mud from Mission Bay and from the Channel Island region. To demonstrate the presence of hydrocarbon-oxidizing bacteria in these materials, small amounts of the sediment were added to tubes containing 75% sea water, 0.1% NH4Cl and a large drop of sterile paraffin oil. Uniform turbidity in the tubes or a pellicle of growth at the oil-water interface after 7 to 9 days incubation indicated the presence of these organisms. These cultures were purified by repeated transfers and by plating procedures. Using this technic, cultures able to oxidize a variety of hydrocarbons have been isolated from most of the sediments tested.

To test hydrocarbon-oxidation in the sediments, the muds were mixed with sterile paraffin oil, or in some cases a lubricating oil, and were added to sterile bottles. Oxidation of the hydrocarbon was determined by the extent of oxygen consumption which was measured manometrically.

Table I shows the results of a typical experimerit in which 50 g of sediment from Mission Bay were used. The test cultures contained 2 ml of the particular oil. The controls represent biological oxidation of the organic matter in the muds. It is evident that considerable O₂ was consumed in the presence of the hydrocarbon.