Researchers have discovered a whole new cycle of natural hydrocarbon emissions and the recycling facilitated by a variety of microorganisms.
Earth scientist Connor Love of the University of California, Santa Barbara (UCSB) said: “There are only two marine cyanobacteria adding up to 500 times more hydrocarbons to the ocean annually, more than the sum of all other types of petroleum input to the ocean, including This is natural oil spills, oil spills, fuel dumping, and surface runoff from the ground. “
But unlike the more familiar human contributions of hydrocarbons to our ocean, this is not a one-way local discharge.
These hydrocarbons, mainly in the form of pentadecane (nC15), diffuse across 40% of the Earth’s surface, and other microbes feed on them. They are being cycled frequently in a way that Love and colleagues estimate that there are only about 2 million metric tons in water at any given time.
“Every two days all the pentadecans are produced and consumed in the ocean,” Love said.
Today, humankind’s hydrocarbon traces can be found in most aspects of our ocean. And we emit these molecules made of carbon and hydrogen atoms in a number of ways – bulk through the extraction and use of fossil fuels, but also from plastics, cooking, candles and paint, the list goes on. So perhaps it should come as no big surprise that the impacts of our emissions have overwhelmed our ability to see the enormous hydrocarbon cycle, which is occurring naturally in our oceans.
It took Loew and his colleagues some effort to clearly define this global cycle for the first time.
Out of most human sources of hydrocarbons, in the nutrient-poor subtropical waters of the North Atlantic, the team had to position the vessel they sampled against the winds, so the diesel fuel that also contains the pentadecan did not contaminate the seven study sites. No one was allowed to cook, smoke or paint on the deck during the assembly.
Earth scientist David Valentine, of UCSB, explained: “It is like the Golden Gate Bridge: you start at one end and when you reach the other, it is time to start over.”
Returning to land, the researchers were able to confirm that the pentadecane in seawater samples was of biological origin, using gas chromatography.
When analyzing their data, they found that pentadecan concentrations increased with a greater abundance of cyanobacteria cells, and the geographic and vertical distribution of the hydrocarbon was consistent with the environment of these microbes.
(Luke Thompson, Chisholm Lab / Nikki Watson, MIT)
The cyanobacteria “Prochlorococcus” and Synechococcus are responsible for about a quarter of the global ocean’s conversion of sunlight energy into organic matter (primary production), and previous laboratory cultivation revealed that they produce pentadecane in the process.
Valentine explains that cyanobacteria would likely use pentadecane as a stronger component of highly curved cell membranes, such as those found in chloroplasts (the organelle that does photosynthesis).
The pentadecan cycle in the ocean was also followed by the circular circulation of these cyanobacteria – their vertical migration in the water in response to changes in light intensity throughout the day.
(David Valentine / UCSB)
Collectively, these results indicate that cyanobacteria are indeed the biological source of pentadecane, which is then consumed by other microorganisms that produce carbon dioxide that the cyanobacteria use to continue the cycle.
Love’s team identified dozens of surface-dwelling bacteria and archaea that thrived in response to the addition of pentadecane in their samples.
The researchers added petroleum hydrocarbons to samples increasingly closer to areas with active spills of oil in the Gulf of Mexico.
Unfortunately, only sea samples from areas already exposed to non-biological hydrocarbons contained microbes that thrived in response to the consumption of these particles.
DNA tests showed that the genes that are believed to encode proteins that can degrade these hydrocarbons differ between microbes, with a clear contrast between those that ingested biological hydrocarbons and those that ate the petroleum source.
“We showed that there is a huge and fast hydrocarbon cycle taking place in the ocean, and it differs from the ocean’s ability to respond to oil input,” Valentin said.
The researchers set out to sequence the genomes of microbes in their sample to understand the ecology and physiology of creatures involved in Earth’s natural hydrocarbon cycle.
This research has been published in a journal Nature Microbiology.