DNA-Based Molecular Surveys of Oilfield Bacterial Communities

Matthew N. Ashby and Dago Dimster-Denk
Taxon Biosciences, Inc, Tiburon, CA

Surface geochemical exploration methods rely on the direct or indirect detection of vertically migrating hydrocarbons. These compounds are subject to numerous microbial transformations that may muddle interpretation of sample surveys. While microbiological surveys can reveal the presence of organisms that mediate these transformations, a limitation to this approach is that the vast majority (>99%) of soil bacteria cannot be cultivated. A solution to this ‘cultivation bottleneck' is to employ molecular, DNA-based detection methods. A U.S. Department of Energy-funded project was initiated to test the utility of a new bacterial profiling technology termed SARD (Serial Analysis of Ribosomal DNA) at resolving complex microbial communities.

Bacterial DNA was examined from twelve near-surface soil samples collected from producing oilfields in California, Texas and Wyoming. Analysis of these samples revealed the presence and abundance of over 2,000 distinct bacterial sequences with only about 25% corresponding to known bacterial species. Correlation analysis revealed that a subset of the bacterial communities showed a significant co-occurrence with propane and butane. Furthermore, none of the bacteria harboring these sequences have been identified previously. Surveys of the distribution of these bacterial species in prospective oilfields revealed likely hydrocarbon microseepage patterns. Thus, the SARD method represents a robust new tool for characterizing biological and geochemical interactions with practical applications.

AAPG Search and Discovery Article #90039©2005 AAPG Calgary, Alberta, June 16-19, 2005