Following the terrible aftermath of an oil spill, usually the smallest of the organisms that do most of the cleaning. Surprisingly, scientists know very little about the tools that these little cleaning crews have at their disposal.
But now, thanks to a new study, researchers have discovered a whole new cycle of natural emissions and recycling of hydrocarbons, facilitated by a diverse range of tiny organisms – which could help us better understand how some microbes have the power to clean up the mess of an oil spills leaves into the ocean.
“Only two types of marine cyanobacteria add 500 times more hydrocarbons to the ocean per year than the sum of all other types of oil inputs into the ocean, including natural oil spills, oil spills, fuel runoff and land runoff.” said Earth scientist Connor Love of the University of California, Santa Barbara (UCSB).
But unlike the better-known human contributions of hydrocarbons to our ocean, this is not a one-way local dump.
These hydrocarbons, mainly in the form of pentadecane (nC15), are spread over 40% of the Earth’s surface, and other microbes are celebrated on them. They are constantly cycled in such a way that Love and his colleagues estimate that around 2 million metric tons are present at any given time.
“Every two days you produce and consume all the pentadecane in the ocean,” Love explained.
(Luke Thompson, Chisholm Lab / Nikki Watson, MIT)
Above: A globally distributed species of marine cyanobacteria, Prochlorococcus.
Today, the hydrocarbon footprints of humanity can be found in most aspects of our surroundings. We emit these molecules composed only of carbon and hydrogen atoms in many ways – mostly through the extraction and use of fossil fuels, but also plastics, cooking, candles, painting and the list goes on.
So it should probably not be a huge surprise that the traces of our own emissions have drowned out our ability to see the huge hydrocarbon cycle that occurs naturally in our oceans.
Love and colleagues needed effort to clearly identify this global cycle for the first time.
Far from most human sources of hydrocarbons in the nutrient-poor subtropical waters of the North Atlantic, the team had to position the ship from which samples were taken to withstand the wind, so that diesel containing pentadecane did not contaminate the seven sites. study. No one was allowed to cook, smoke or paint on the deck during the collections.
“I don’t know if you’ve ever been on a ship for an extended period of time, but you paint every day,” said UCSB Earth scientist David Valentine. “It’s like the Golden Gate Bridge: you start from one end and until you reach the other end it’s time to start over.”
Back on land, the researchers were able to confirm that the pentadecane in their seawater samples was of biological origin, using a gas chromatograph.
Analyzing their data, they found that pentadecan concentrations increased with a higher abundance of cyanobacterial cells, and the geographical and vertical distribution of the hydrocarbon was consistent with the ecology of these microbes.
Cyanobacteria Prochlorococcus and Sinechococcus are responsible for about a quarter of the transformation of the ocean at the level of solar energy into organic matter (primary production), and previous cultivation in the laboratory revealed that they produce pentadecane in this process.
Valentine explains that cyanobacteria probably use pentadecane as a stronger component for highly curved cell membranes, such as those found in chloroplasts (the organ that photosynthesizes).
The pentadecane cycle in the ocean also follows the diel cycle of these cyanobacteria – their vertical migration into water in response to changes in light intensity during a day.
Together, these findings suggest that cyanobacteria are indeed the source of biological pentadecane, which is then consumed by other microorganisms that produce the carbon dioxide that cyanobacteria then use to continue the cycle.
The natural cycle of the Earth’s hydrocarbons. (David Valentine / UCSB)
Love’s team identified dozens of bacteria and surface archaea that blossomed in response to the addition of pentadecane to their samples.
So they then tested to see if hydrocarbon-consuming microbes could also break down oil. The researchers added an oil hydrocarbon to samples increasingly closer to areas with active oil spills in the Gulf of Mexico.
Unfortunately, only sea samples from areas already exposed to non-biological hydrocarbons contained microbes that flourished in response to the consumption of these molecules.
DNA tests have shown that genes that are thought to encode proteins that can degrade these hydrocarbons differ between microbes, with a stark contrast between those that consumed biological hydrocarbons and those that devoured those from oil.
“We have shown that there is a massive and rapid hydrocarbon cycle that takes place in the ocean and that it is distinct from the ocean’s ability to respond to oil supply,” Valentine said.
The researchers began sequencing the genomes of the microbes in their sample to further understand the ecology and physiology of the creatures involved in the Earth’s natural hydrocarbon cycle.
“I guess [these findings reveal] how much we don’t know about the ecology of many hydrocarbon consuming organisms, “Love said.
This research was published in The microbiology of nature.