After the Deepwater Horizon disaster in 2010, microbes in the Gulf of Mexico devoured a major portion of the hydrocarbons released by the gushing deep-sea well. A new study offers an explanation for what bacteria like these might live off of in the absence of a massive oil spill: alkanes produced by photosynthetic cyanobacteria.
“People have known for a while that bacteria play a large role in breaking down oil spills,” says David Lea-Smith of the University of Cambridge, who led the research. “This study gives a hypothesis for why those bacteria are there.”
Scientists have known that cyanobacteria, also known as blue-green algae, can synthesize hydrocarbons. In the new study, Lea-Smith and colleagues at the University of Warwick and MIT estimated the microbes’ global hydrocarbon production.
They grew cultures of the two most abundant cyanobacteria genera in oceans, Prochlorococcus and Synechococcus, and then measured the amounts of hydrocarbons produced per cell. The cyanobacteria mainly generated the straight-chain hydrocarbons pentadecane, heptadecane, and 8-heptadecene.
Using ocean population data for Prochlorococcus and Synechococcus, the team estimated that cyanobacteria produce up to 800 million tons of hydrocarbons every year (Proc. Natl. Acad. Sci. USA 2015, DOI: 10.1073/pnas.1507274112). In comparison, the U.S. produced about 700 million tons of petroleum and other hydrocarbon liquids in 2014, the most of any nation that year, according to the U.S. Energy Information Administration.
The researchers also demonstrated that hydrocarbon-degrading bacteria could live and grow on low levels of heptadecane, leading the scientists to propose that these microbes could survive on the alkanes produced by cyanobacteria.
David L. Valentine, a biogeochemist at the University of California, Santa Barbara, who studied the biodegradation of oil during the Deepwater Horizon disaster, thinks the study’s conclusions are intriguing. But he points out that oil-degrading bacteria also break down complex types of hydrocarbons in oil, so there must be non-cyanobacteria sources of those types of molecules in the ocean, such as natural oil seeps.