As a result of an oil spill, it is usually the smaller organisms that do most of the cleaning. Surprisingly, scientists know very little about the tools these small cleaning crews have.
But now, thanks to a new study, researchers have discovered a completely new cycle of natural hydrocarbon emissions and recycling facilitated by a diverse range of tiny organisms, which could help us better understand how some microbes have the power. to clean the mess and oil. shed leaves in 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 leaks, oil spills, fuel spill and land runoff, ”said Connor Love, an Earth scientist at the University of California, Santa Barbara (UCSB).
But unlike the more familiar human hydrocarbon contributions to our ocean, this is not a one-way local landfill.
These hydrocarbons, mainly in the form of pentadecane (nC15), spread over 40 percent of the Earth’s surface, and other microbes are celebrated. They are constantly circulating so Love and his colleagues estimate that there are only about 2 million metric tons in the water at a time.
“Every two days all the pentadecane is produced and consumed in the ocean,” Love explained.
(Luke Thompson, Chisholm Lab / Nikki Watson, MIT)
Above: a species of marine cyanobacteria distributed worldwide, Prochlorococcus.
Today, the hydrocarbon footprints of humanity can be found in most aspects of our environment. 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 from plastics, cooking, candles, paint, and the list goes on.
Therefore, it should probably not be a big surprise that the traces of our own emissions drown our ability to see the immense hydrocarbon cycle that occurs naturally in our oceans.
Love and her colleagues needed some effort to clearly identify this global cycle for the first time.
Far from most sources of human hydrocarbons, in the nutrient-poor subtropical waters of the North Atlantic, the team had to locate the ship from which they took samples to face the wind, so that the diesel that also contains pentadecane did not contaminate the seven sites in the 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,” Earth scientist David Valentine of the UCSB explained. “It’s like the Golden Gate Bridge: you start at one end and when you get to the other end it’s time to start again.”
Back on land, the researchers were able to confirm that the pentadecane in their seawater samples was of biological origin by using a gas chromatograph.
Analyzing their data, they found that pentadecane concentrations increased with an increased abundance of cyanobacterial cells, and the geographical and vertical distribution of the hydrocarbon was consistent with the ecology of these microbes.
Cyanobacteria Prochlorococcus i Sinecococcus they are responsible for about a quarter of the global ocean’s conversion of solar energy into organic matter (primary production) and pre-laboratory cultivation revealed that they produce pentadecane in the process.
Valentine explains that cyanobacteria probably use pentadecane as a stronger component for highly curved cell membranes, such as those found in chloroplasts (the organelle that does photosynthesis).
The pentadecane cycle in the ocean also follows the dielial cycle of these cyanobacteria: their vertical migration to water in response to changes in light intensity over the course of a day.
Together, these findings suggest that cyanobacteria are in fact the source of biological pentadecane, which is then consumed by other microorganisms that produce the carbon dioxide that cyanobacteria use to continue the cycle.
Natural cycle of the Earth’s hydrocarbons. (David Valentine / UCSB)
Love’s team identified dozens of bacteria and surface archaea that flourished in response to the addition of pentadecane to their samples.
They then tested whether microbes consuming hydrocarbons could also break down oil. The researchers added an oil hydrocarbon to samples getting closer to areas with active oil leaks, in the Gulf of Mexico.
Unfortunately, only marine samples from areas already exposed to non-biological hydrocarbons contained microbes that flourished in response to the consumption of these molecules.
DNA testing showed that genes designed to encode proteins that can degrade these hydrocarbons differed between microbes, with a stark contrast between those who ate organic hydrocarbons and those who devoured petroleum products.
“We showed that there is a massive, rapid hydrocarbon cycle that occurs in the ocean and that it is different from the ocean’s ability to respond to oil input,” Valentine said.
Researchers have begun 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 think [these findings reveal] how much we don’t know about the ecology of many organisms that consume hydrocarbons, ”Love said.
This research was published in Microbiology of nature.