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Characterization of microorganisms associated with Helaeomyia petrolei (oil fly) larvae

Dana Renee Kadavy, University of Nebraska - Lincoln


Helaeomyia petrolei larvae isolated from the asphalt seeps of Rancho La Brea, Los Angeles were examined for microbial gut contents. Despite the ingestion of large amounts of potentially toxic asphalt by the larvae, their guts sustained the growth (ca. 2 × 105 heterotrophic bacteria per larvae) of 100–1000 times more bacteria than did free oil. Of fourteen isolates cultured and identified aerobically, nine were identified as Providencia rettgeri and three were likely Acinetobacters. Two isolates were cultured under anaerobic techniques, one was identified as a Clostridium (closest identity to C. sporogenes) and the other positively identified as Enterococcus faecalis. All nine of the strains classified as Providencia exhibited multiple antibiotic resistance that was not due to elevated mutation rates. The resistance properties of the oil fly bacteria extend to organic solvents as well as antibiotics. Seven of the nine Providencia strains were considered extremophiles in their ability to tolerate overlays of 100% cyclohexane on agar plates. Six of the nine isolates also tolerated 10% xylene, benzene or toluene (10:90 vol./vol. in cyclohexane) and three of the nine tolerated overlays of 50% xylene-50% cylcohexane. P. rettgeri strain OF011 also grew well in liquid culture saturated with 10.0% cyclohexane. Mechanisms of solvent tolerance in Providencia were examined. Changes at the outer membrane level (alteration in LPS or capsule formation) did not appear to contribute to solvent tolerance. The correlation between antibiotic resistance and organic solvent tolerance in P. rettgeri suggests at least one mechanism of resistance to be an active efflux pump. Although a portion of the P. rettgeri -OF011 genome shared sequence homology to other known efflux pump proteins, efforts to clone the gene responsible have been unsuccessful. The two anaerobic isolates C. sporogenes and E. faecalis , were able to grow in liquid cultures supplemented with 1 or 5% acetone, butanol and cyclohexane, suggesting these are some of the most solvent tolerant gram-positive organisms characterized to date. ^

Subject Area

Biology, Microbiology

Recommended Citation

Kadavy, Dana Renee, "Characterization of microorganisms associated with Helaeomyia petrolei (oil fly) larvae" (2001). ETD collection for University of Nebraska - Lincoln. AAI3009729.