Research finds bacteria behind tar pits’ bubbles

LOS ANGELES – Like many other visitors to the Rancho La Brea Tar Pits, sisters Samantha and Katie Salazar watched a basketball-sized bubble emerge from dark, slimy gunk Sunday and wondered, why are the tar pits bubbly?

For years, educators at the site could only guess that methane gas was being released as the by-product of oil creation 1,000 feet below the surface.

Researchers at the University of California, Riverside finally have found the answer: Gangs of hardy bacteria embedded in the natural asphalt are eating away at the petroleum and burping up methane.

From the bacteria the researchers isolated in tar pit samples, about 200 to 300 of them are previously unknown species.

“I was totally surprised but totally delighted,” said John Harris, a paleontologist who is chief curator at the Page Museum, where the fossils from the tar pits are collected. “The tar pits are world famous already for fossils, but this is another claim to fame.”

Since the early 20th century, scientists and volunteers scouring the tar pits have found bones, shells, trunks and leaves from some 600 kinds of animal and plants from the last Ice Age; the fossils range in age from 11,000 to 40,000 years old. The pits have yielded mammoths, saber-tooth cats, a condor-like bird known as Merriam’s Teratorn and coastal redwood trees.

While scientists previously had found one living thing in the asphalt – an oil fly that lays its larvae there – no one had managed to extract bacteria.

David Crowley, one of the Riverside scientists who found the new bacteria, and Jong-Shik Kim, a post-doctoral research associate, realized that they could pour cold liquid nitrogen on the asphalt, crush it into a fine powder and extract bacterial DNA from this powdered form.

“We found some really great bacteria,” said Crowley, 54. “The types we found are all very specialized for life in extreme environments.”

The bacteria found in the pits work as a part of a community. They eat up the petroleum and make organic acids, such as acetic acid, the compound that creates the sour flavor in vinegar. Other bacteria, which Crowley and Kim are still working to characterize, consume these acid by-products and produce the methane that bubbles to the surface.

What makes these petroleum-eating bacteria interesting is their potential environmental application, Crowley said. Their ability to break up complex hydrocarbons could help clean oil spills or clear the holds of oil tankers.

Katie Salazar, 9, pronounced the discovery “amazing” and planned to include the new information in a school report she was writing on the tar pits.