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Biogeochemistry

Oil spill first responders: how tiny algae cultivate oil-degrading bacteria

The paper:

David J. Lea-Smith, Steven J. Biller, Matthew P. Davey, Charles A. R. Cotton, Blanca M. Perez Sepulveda, Alexandra V. Turchyn, David J. Scanlan, Alison G. Smith, Sallie W. Chisholm, and Christopher J. Howe (2015) Contribution of cyanobacterial alkane production to the ocean hydrocarbon cycle, PNAS 112 (44) 13591-13596, doi:10.1073/pnas.1507274112

 

Background: oil spill first responders

Oil spills are devastating for marine life, but fortunately nature has a built-in disaster squad: oil-eating bacteria show up soon after spills and degrade the mess fairly quickly, sparing us the worst effects. How this happens is a bit of a mystery. Oil is difficult to digest even for bacteria, and most organisms with the enzymes necessary for eating oil can’t survive with any other food source. Yet whenever there’s a spill in parts of the ocean with no known sources of oil pollution (for example, the Exxon Valdez spill off the coast of Alaska in 1989), the oil degrading community is on the scene quickly. They appear to be present wherever we look for them, but how do they survive in the absence of their only food source?

This study shows that cyanobacteria, the smallest and most abundant class of photosynthetic algae produce significant amounts of alkanes, a chemical class comprising about 50% of crude oil. David Lea-Smith, and a group of researchers from University of Cambridge and MIT, hypothesized that these cyanobateria produce enough of the chemical to support an oil-consuming bacterial community around the world. This process cultivates a natural set of first-responders whenever a disastrous oil spill occurs.

Oil production by cyanobacteria

First, the authors analyzed the genomes of Prochlorococcus and Synechococcus, the two most abundant types of cyanobacteria and showed that they have the enzymatic machinery to produce alkanes. Next, they analyzed the alkane content of the cyanobacteria themselves. The amount of alkane per organism was incredibly tiny, less than a quarter of 1% of each cell’s weigh, and since the bacteria themselves are so small, that works out to less than a femtogram of alkanes per cell—that’s 10-15, or a millionth of a billionth of a gram! But because cyanobacteria are so abundant and the ocean is so large, this corresponds to the production of as much as 500 million tons of alkanes per year across the world’s oceans. For comparison, the Deepwater Horizon oil spill — the largest and most devastating marine oil spill in history — released about half a million tons of crude oil into the Gulf of Mexico.

Figure 1: Concentration of three different species of oil-degrading bacteria (A,B, and C) during incubation experiments. All three survived and multiplied when mixed with oil or heptadecane (one of the alkanes produced by cyanobacteria), but mostly died off when oil was not added.

Figure 1: Concentration of three different species of oil-degrading bacteria (A,B, and C) during incubation experiments. All three survived and multiplied when mixed with oil or heptadecane (one of the alkanes produced by cyanobacteria), but mostly died off when oil was not added.

 

Finally, the authors performed a series of incubation experiments with oil-degrading bacteria. They added either crude oil or the alkanes produced by cyanobacteria to a culture of the bacteria, while incubating other cultures without oil as a control. The bacteria in the control group without added oils died quickly, but the crude oil and alkane cultures thrived, demonstrating that they need a constant source of oil to survive (Figure 1). Cyanobacteria are the most likely source for that oil in non-spill conditions, and a back-of-the-envelope calculation based on the results of the experiments shows that the size of the microbial population that could be supported by cyanobacterial oil production matches the size of the oil-degrading community found in unpolluted natural waters.

Significance and implications

This study helps explain an apparent paradox: oil degraders need a constant supply of oil to survive, but always

Figure 2: The short and long term hydrocarbon cycles in the ocean. In the short term cycle, cyanobacteria produce alkanes that are rapidly degraded by the hydrocarbon-degrading bacterial community, preventing oil from accumulating. This maintains an active oil-degrading community capable of rapidly responding to an oil spill and breaking down toxic compounds (the long term hydrocarbon cycle).

Figure 2: The short and long term hydrocarbon cycles in the ocean. In the short term cycle, cyanobacteria produce alkanes that are rapidly degraded by the hydrocarbon-degrading bacterial community, preventing oil from accumulating. This maintains an active oil-degrading community capable of rapidly responding to an oil spill and breaking down toxic compounds (the long term hydrocarbon cycle).

seem present and ready to go when a spill does occur, even in areas with a low baseline of oil contamination. Cyanobacteria appear to provide a vital service in bridging the gap by producing enough alkanes to keep oil-degrading microbes from starving, and able to quickly break down oil spills no matter where they occur (Figure 2).While oil spills are still devastating to marine ecosystems, this system limits the persistence of one of the largest components of oil. It’s an accident of nature that makes the ocean far more resilient to catastrophes like oil spills than we might expect.

Discussion

2 Responses to “Oil spill first responders: how tiny algae cultivate oil-degrading bacteria”

  1. Oil spill first responders: how tiny algae cultivate oil-degrading bacteria
    By Michael Philben
    Cyanobacteria is a type of bacteria that has the enzymes to digest oil. This helps ocean life from being as exposed to oil as usual. For example when an oil spill occurs, the cyanobacteria shows up and degrades some of the oil. The bacteria makes alkanes that are the things that degrade oil from oil spills. Cyanobacteria is a type of bacteria , the two largest types of cyanobacteria these two types of cyanobacteria produce the most alkane to degrade oil. Cyanobacteria itself only produces a small amount of alkane. Although the production of alkane that is the enzyme that degrades oil is very sparse there are millions of cyanobacteria and there are millions of square miles of the ocean. This bacterium cannot survive without the crude oil. From reading this article I learned that there are various different ways to clean up an oil spill. For example, there is the cyanobacteria method, there is the kitty litter method, and the pantyhose method. Theses methods are green ways to help stop oil spills and that doesn’t hurt the environment or the ocean. Cyanobacteria is also already existing in the ocean so the cost is not an issue like other ways are. I would like to get more involved in ways to help clean up and prevention of oil spill. For example, if we aren’t doing anything to fix this problem we might not have an ocean left. I would like to know ways that people can help oil spills that can’t physically go to the beach or place where it is occurring.

    Posted by Mariyam | March 8, 2017, 2:18 pm
  2. It is quite amazing to know something as small as bacteria can be a significant component to cleaning up an oil spill. I didn’t know that cyanobacteria were able to produce great amounts of alkanes. How are cyanobacteria able to produce that much? I also didn’t know cyanobacteria can produce as much as 500 million tons of alkanes per year. Considering the amount of alkane is less than a quarter of 1% of each cell’s weight, it is quite baffling to know that cyanobacteria can produce that amount of alkanes per year. But I have a question in mind: Can cyanobacteria alone be able to get rid of oil spills? If not, why? Taking that they feed on oil, why are there other solutions of getting rid of oil in oceans taking place?

    Posted by Jeannie | March 5, 2017, 11:43 pm

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