One animal beautifully adapted to the viscous asphalt of the La Brea tar pits is the oil fly Helaeomyia petrolei (Syn. Psilopa). As a normal part of its carnivorous existence the oil fly larval guts are filled with tar, with no adverse effects. Surface sterilized larvae 5 contained ca. 2 x 10 heterotrophic bacteria per larva. These bacteria have been identified as a mixture of enteric bacteria, most commonly Providencia rettgeri, and Acinetobacter spp. These bacteria were clearly growing because their numbers in the larval guts were 100 to 1,000 times greater than in free oil/asphalt. There is no evidence yet that these bacteria can degrade the complex aromatic hydrocarbons of the tar/asphalt. However, the bacteria isolated are highly solvent tolerant and they remain a potential source of hydrocarbon/solvent tolerant enzymes. Likely of greatest evolutionary interest, these bacteria were naturally resistant to 9 of 23 common antibiotics tested. This finding suggests that the oil fly bacteria have an active efflux pump for aromatic hydrocarbons, due to the constant selective pressure of La Brea’s solvent-rich environment. We suggest that the oil fly bacteria and their genes for solvent tolerance may provide a microbial reservoir for antibiotic resistance genes
