Cyanobacteria are amongst the most abundant organisms on the planet and massively impact the global ecosystem. Cyanobacteria were likely responsible for generating an oxygenic atmosphere ~2.3 billion years ago which allowed for development of more complex organisms. Today, cyanobacteria are responsible for approximately a quarter of global carbon fixation and the majority of marine nitrogen fixation.
Cyanobacteria and the environment
Trichodesmium erythraeum IMS101, an important nitrogen fixing cyanobacterium
We are interested in the impact of cyanobacteria on global biogeochemical cycles. For example, we have been investigating the role of long chain hydrocarbons on the environment. All cyanobacteria have the capacity to produce hydrocarbons, predominantly alkanes such as pentadecane and heptadecane. Both compounds are major constituents of diesel fuel. In collaboration with MIT and the University of Warwick we published the first work investigating the scale of hydrocarbon production in marine environments. We provided estimates of hydrocarbon production by the two most abundant cyanobacteria on Earth, Prochlorococcus and Synechococcus, which varied between 300-800 million tonnes per annum. The higher figure is similar to the amount of crude oil produced by Saudi Arabia each year. Based on the low amounts of hydrocarbons observed in the ocean, these compounds are likely degraded by other bacteria, evaporate into the atmosphere or sink to the ocean floor. We demonstrated that hydrocarbon-degrading bacteria consume cyanobacterial alkanes, releasing carbon dioxide, which in turn is utilised by cyanobacteria. We termed this process ‘the short-term hydrocarbon cycle’, since it likely occurs over a period of days. Our hypothesis is that cyanobacterial alkanes maintain a population of hydrocarbon degrading organisms, which rapidly expand in number following crude oil release into the environment. The hydrocarbon degrading bacterium consume the oil, thereby limiting damage to the local ecosystem. However, further work is required to validate this hypothesis.
The marine hydrocarbon cycle (Lea-Smith et al, 2015)
Lea-Smith DJ, Biller SJ, Davey MP, Cotton CAR, Perez Sepulveda BM, Turchyn AV, Scanlan DJ, Smith AG, Chisholm SW, Howe CJ (2015). Major contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle. PNAS 112 (44), 13591-13596.
Dr Sascha Turchyn, Department of Earth Sciences, University of Cambridge
Dr Jonathon Todd, School of Biological Sciences, University of East Anglia
Dr Nikolai Pedentchouk, School of Environmental Sciences, University of East Anglia
Professor Xiao-Hua Zhang, College of Marine Life Sciences, Ocean University of China, Qingdao, China