Microbiologists at the University of Texas at Austin have cracked the genetic code of how bacteria broke down oil to help clean up the Deepwater Horizon oil spill and disovered that some bacteria have far greater potential for consuming oil than was previously known—and have implications for responding to future oil spills and other ecological disasters.

Since the spill in the Gulf of Mexico, scientists have studied how communities of bacteria that grew exponentially after the disaster helped to eat away at the vast range of chemicals there, but little was known about the genetic underpinnings of the process. Brett Baker, assistant professor in the Department of Marine Science; Nina Dombrowski, a postdoctoral researcher in his lab at the University of Texas Marine Science Institute; and colleagues sequenced the DNA of oil-munching microbes to reveal the genetic potential in different bacterial species, including ones newly identified as important to the cleanup task.

The surface oil slick from the Deepwater Horizon oil spill. Image credit: Andreas Teske, UNC- Chapel Hill."Oil is extremely complicated but it has two major compounds: alkanes, which are relatively easy for bacteria to break down, and aromatic hydrocarbons, which are much trickier to get rid of," Dombrowski says. "We found a number of bacteria surprisingly capable of dealing with the more dangerous compounds."

One bacterium known to have oil-eating abilities, Alcanivorax, was previously thought incapable of consuming the more stable hydrocarbons the spill left behind. Others, like Neptuniibacter, weren't known to be involved with degrading oil in the Gulf. Not only did gene sequencing show several bacteria could break down aromatic hydrocarbons, it illuminated how various species worked together to maximize the genetic potential of the whole microbial community.

The scientists catalogued the genes of numerous bacteria from the Deepwater Horizon oil spill to figure out how microbes gobble up the complex mix found in oil, which consists of as many as 1,000 types of chemical compounds. The researchers pinpointed specific pathways where members of the complex, native bacterial community work together to consume oil.

"It's equivalent to a concert," Dombrowski says. "All the musicians have to work together to make a piece of beautiful music. After the spill, all bacteria must work together to efficiently degrade oil."

The scientists also found that some bacteria assist with the "cleanup after the cleanup," meaning they also could eat what humans pour into the water to clean up the oil. These dispersants can cause environmental problems themselves. The DNA sequencing revealed evidence that some bacteria can degrade sulfur-containing compounds such as those found in dispersants used after the Deepwater Horizon spill.

Not all bacteria respond well to dispersants, however, and Dombrowski says the importance of "bacteria-friendly" dispersants that will not interfere with this microbial teamwork is clear. Understanding how bacteria are genetically programmed to eat oil provides scientists with clues for how to create better dispersants and ocean-cleanup strategies.

"Bacterial communities already present at the site of an oil spill can respond in a rapid and efficient manner, becoming abundant during the spill and actively degrading oil compounds," Dombrowski says. "This illustrates the importance of maintaining a healthy and diverse bacterial community—and why we need to be careful to make sure our response to a spill doesn't interfere with this natural response."