S22: Analysis of microbial community structure in crude oil and oil spill samples using phospholipid fatty acid analysis

Phospholipid fatty acids (PLFA) are principle components of cell membranes which have been used to determine community structure in a wide variety of environments.  Because PLFA are only extracted from viable biomass only active or predominant  species are detected.  In addition lipid biomarkers can be used to study environmental toxicity or stress.  PLFA methods were adapted to investigate community structure in oil samples, including crude oil and oil/water mixtures.  Since most of the oil was extracted with the lipid fraction, addition separation techniques were necessary to remove the oil from the lipid extract.  Efficiency of the extraction was quantified with pure cultures and use of an internal standard.  PLFA extracts from crude oil showed bacterial numbers from 10⁵ to 10⁷ cells/ml.  Higher cell numbers were found from wells with increased biodegradation of oil.  Predominant biomarkers were for gram negative bacteria, sulfate reducers, and Pseudomonas sp, and archaeal lipids were detected in all samples.   These techniques will be applied to Deepwater Horizon samples from Mississippi Canyon to investigate microbial community structure as a function of depth, location, and time in the Gulf of Mexico in response to the BP oil spill.