Date Awarded


Document Type


Degree Name

Doctor of Philosophy (Ph.D.)


Virginia Institute of Marine Science


Bacterial populations indigenous to surface (1 m) waters of the Middle Atlantic Outer Continental Shelf were sampled at seasonal intervals to determine the abundance and distribution of petroleum-degrading (HC) and "total" heterotrophic (HET) bacteria. Simultaneously, unweathered South Louisiana crude oil (SLCO) was added to aliquots of surface water samples to evaluate rates and patterns of degradation of hydrocarbon. Degradation was studied using selected nutrient and temperature regimes in both closed flask and prototype "open" or continuous dilution systems. HET bacterial levels generally decreased with distance from land (x inshore = 6 x 10('4) MPN/ml to x offshore = 6 x 10('2) MPN/ml). HC bacteria were most abundant in the coastal boundary layer (x = 2 x 10('2) MPN/ml). Changes in values of HC/HET often were not directly related to the abundance of petroleum-degrading bacteria. In closed flasks the composition of bacterial populations changed slightly in response to SLCO addition; Pseudomonas predominated after 48 days. Pseudomonas isolates exhibited the greatest ability for petroleum degradation in pure cultures. Degradation of SLCO in closed flasks characteristically resulted in removal of n-alkanes and selected aromatics at rates related to season, sampling location, and nutrient regime. Aromatic compounds were often removed concomitantly with n-alkanes. Although maximum rates of degradation were observed at 15�C using coastal water inocula and inorganic nutrient enrichment, all shelf waters sampled contained bacteria capable of petroleum degradation.



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