ANAEROBIC OXIDATION OF HYDROCARBONS IN CRUDE-OIL BY NEW TYPES OF SULFATE-REDUCING BACTERIA

MANY crude oil constituents are biodegradable in the presence of oxyge n; however, a substantial anaerobic degradation has never been demonst rated(1,2). An unusually low content of n-alkanes in oils of certain d eposits is commonly attributed to selective utilization of these hydro carbons by aerobic microorganisms(3,4). On the other hand, oil wells a nd production fluids were shown to harbour anaerobic sulphate-reducing bacteria(5-8), but their actual electron donors and carbon sources we re unknown. On the basis of nutritional properties of various bacteria l isolates it was assumed that fatty acids and H-2 are potential elect ron donors for sulphate reduction in situ(5-8). Here we demonstrate th at hydrocarbons in crude oil are used directly by sulphate-reducing ba cteria growing under strictly anoxic conditions. A moderately thermoph ilic pure culture selectively utilizes n-alkanes in oil for sulphate r eduction to sulphide. In addition, a mesophilic sulphate-reducing enri chment culture is shown to oxidize alkylbenzenes in oil. Thus, sulphat e-reducing bacteria utilizing aliphatic and aromatic hydrocarbons as e lectron donors may present a significant source of sulphide in oil dep osits and oil production plants.