Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle.

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Lea-Smith, David J 
Biller, Steven J 
Davey, Matthew P 
Cotton, Charles AR 
Perez Sepulveda, Blanca M 

Hydrocarbons are ubiquitous in the ocean, where alkanes such as pentadecane and heptadecane can be found even in waters minimally polluted with crude oil. Populations of hydrocarbon-degrading bacteria, which are responsible for the turnover of these compounds, are also found throughout marine systems, including in unpolluted waters. These observations suggest the existence of an unknown and widespread source of hydrocarbons in the oceans. Here, we report that strains of the two most abundant marine cyanobacteria, Prochlorococcus and Synechococcus, produce and accumulate hydrocarbons, predominantly C15 and C17 alkanes, between 0.022 and 0.368% of dry cell weight. Based on global population sizes and turnover rates, we estimate that these species have the capacity to produce 2-540 pg alkanes per mL per day, which translates into a global ocean yield of ∼ 308-771 million tons of hydrocarbons annually. We also demonstrate that both obligate and facultative marine hydrocarbon-degrading bacteria can consume cyanobacterial alkanes, which likely prevents these hydrocarbons from accumulating in the environment. Our findings implicate cyanobacteria and hydrocarbon degraders as key players in a notable internal hydrocarbon cycle within the upper ocean, where alkanes are continually produced and subsequently consumed within days. Furthermore we show that cyanobacterial alkane production is likely sufficient to sustain populations of hydrocarbon-degrading bacteria, whose abundances can rapidly expand upon localized release of crude oil from natural seepage and human activities.

cyanobacteria, hydrocarbon cycle, hydrocarbon-degrading bacteria, hydrocarbons, oil remediation, Alkanes, Bacteria, Biodegradation, Environmental, Ecosystem, Gas Chromatography-Mass Spectrometry, Humans, Hydrocarbons, Oceans and Seas, Petroleum, Prochlorococcus, Seawater, Synechococcus
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Proc Natl Acad Sci U S A
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Proceedings of the National Academy of Sciences
Biotechnology and Biological Sciences Research Council (BB/I00680X/1)
European Research Council (307582)
D.J.L-S. was supported by the Environmental Services Association Educational Trust. S.J.B and S.W.C. were supported by the US National Science Foundation (grant OCE-1356460), the Gordon and Betty Moore Foundation (grant GMBF495), and the Simons Foundation SCOPE project (to S.W.C.). This work was also funded in part by a University of Warwick International Chancellors Scholarship to B.P.S. and by the Natural Environment Research Council (grant NE/I00985X/1) to D.J.S.