Oil-coated water droplets are mini-ecosystems for microbes

Oil-coated water droplets are mini-ecosystems for microbes

by Timothy Oleson Tuesday December 9th, 2014

Oil rising from underground is solidifying into asphalt over much of Pitch Lake on the Caribbean island of Trinidad. In places, it also reaches the surface in liquid form. Credit: Rainer Meckenstock.

Dark, muddy oil may not seem like a suitable environment for life. But microbes known to make such organic stews by breaking down large hydrocarbons to extract food and energy have been found in oil reservoirs before. Now, in a new study, researchers report finding diverse communities of microorganisms living inside tiny water droplets in Pitch Lake, the world’s largest natural asphalt seep located on the Caribbean island from Trinidad. The finding could have implications for the industry, the scientists say, as well as for our understanding of extreme life.

In 2011, a team led by Dirk Schulze-Makuch at Washington State University reported evidence of bacteria and archaea living in Pitch Lake, where oily asphalt slowly oozes onto the Earth’s surface. from underground deposits. But microbes can’t survive on hydrocarbons alone, so the question became, “How do they live in this?” says Schulze-Makuch, co-author of the new study published in Science. Returning to the lake several years later, Schulze-Makuch, lead author Rainer Meckenstock, an environmental microbiologist at Helmholtz Zentrum Munich in Germany at the time of the research (and now at the University of Duisburg-Essen, also in Germany), and their colleagues sampled the site again.

Examining the oil from the lake, the researchers noticed many microscopic bubbles, with a volume of only 1 to 3 microliters. Some contained natural gas, while others were filled with brackish water, which isotopic measurements indicated had also risen from deep underground along with the oil and asphalt.

“The amazing thing was that in each of the water droplets, there was basically a mini-ecosystem made up of all these different types of microbes,” says Schulze-Makuch. In fact, genetic sequencing revealed that each drop contained distinct populations of bacteria and archaea. Further analyzes showed the presence of nutrients like phosphate and ammonia, as well as a range of organic metabolites, indicating that the colonies had everything they needed to survive and were actively breaking down the hydrocarbons in the oil.

Microbes in confined underground oil reservoirs are generally thought to “sit near the bottom of the oil”, in a transition zone between the oil and a layer of water, because they need water (in addition to the food and energy) to survive, says Steve Larter, a University of Calgary petroleum geochemist who was not involved in the Pitch Lake work. The new study is “pretty interesting,” he says, in part because it’s the first time anyone “finds dispersed organisms in small water droplets inside oil,” and not just in a transition layer at the base of the deposit.

The observation that hydrocarbon-consuming microbes can thrive not only in the boundary zones around oil reservoirs, but in the droplets within them “has implications for the assessment of reservoir biodegradation. oil,” Meckenstock and his colleagues noted in the study. It is important for oil companies to understand the state of degradation of the oil they might be trying to pump from the ground “because that defines the quality of the oil [and its] value,” says Meckenstock. “All of a sudden the whole tank has to be seen as one big bioreactor where biodegradation could take place.” The new findings could also shed light on how microorganisms degrade and clean up oil spills on land and at sea.

Even more interesting, Larter says, is what the discovery says about the transport of life in the deep biosphere — the abundance of microscopic life teeming in subterranean sediments and the Earth’s crust. A long-standing question is how fast microbes move underground or from below ground to the surface. They’re thought to move quite slowly, even by geological standards, he says, but this study clearly shows that with a large vertical conduit like an oil seep, “you can potentially move organisms by this mechanism over rather long distances on a geological site”. time scale.

Schulze-Makuch, an astrobiologist, says the findings could also shape ideas about where to look for potential life on Saturn’s moon Titan, which has lakes of hydrocarbons on its surface and possibly an icy ocean of ammonia. and water below. “If we see some kind of coping tools [in the Pitch Lake microbes] to survive or even thrive in liquid hydrocarbons, then we can get an idea of ​​how organisms on Titan might survive,” he says.