Special Molecules Enable Bacteria to Break Down Oil

graphic image of green colored bacteria moving to the left

Biological Strategy

Bacteria

Sam Stier

Image: Gerd Altmann / Pixabay / Free non-commercial use

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Living systems often require chemical elements and chemical compounds, including complex sugars, proteins, and odor-making compounds, to perform critical activities. These compounds exist in various states–solid, liquid, and gas–and are ubiquitous in soil, water, and air. This requires that living systems not only have ways to capture, absorb, or filter them, but also ways to differentiate among them, selecting those that are valuable or harmful. For example, mangrove trees live with their roots in salty water and sediments. Various mangrove species have different strategies for removing salt from the water they take in so that their tissues can use the fresh water.

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The most common liquid used by living systems is water, which they require to survive. But there are many other liquids that provide nourishment, play a role in defense mechanisms, or serve other purposes. Water varies in its availability; it is sometimes plentiful and sometimes very scarce or only available as fog or mist. To minimize the energy required to capture, absorb, or filter liquids, living systems have strategies that take advantage of the unique properties of the given liquid. For example, water moves from a gaseous to liquid state when it encounters a surface colder than the air. Plants in forests that experience fog and clouds more than rain have strategies that condense liquid water from moist air.

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Energy is naturally available in many forms, including kinetic, potential, thermal, elastic, radiant, chemical, and more. All living systems require energy to carry out their many activities, and have developed strategies appropriate to one or more of those forms. For example, some plants maximize their surface area available for capturing radiant energy from the sun while others have strategies to focus scattered light onto photosynthesizing areas.

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Bacteria

Domain Bacteria (“small staff”): L. acidophilus, Staphylococcus

From inside of our own bodies to the deepest parts of the ocean, bacteria have adapted to almost every possible environment. All bacteria are unicellular, microscopic, and lack a membrane-bound nucleus and organelles, and come in three basic shapes: spherical (cocci), rod (bacilli), and spiral (spirilla). Some strains can be deadly, like Staphylococcus aureus (MRSA) while others, like Lactobacillus acidophilus, found in our intestinal microbiome, keep us healthy. Cyanobacteria, also known as blue green algae, caused the Great Oxidation Event 2.4 billion years ago, producing Earth’s first oxygenated atmosphere.

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Unique molecules from bacteria help them digest petroleum, vegetable oil, and coal.

Bacteria come from some of the planet’s most ancient forms of life. Often, bacteria have impressive abilities that are rare in other creatures. Some bacteria, for instance, can actually eat fossil fuels, like petroleum (used to make gasoline) or coal. This ability enables bacteria to survive in places that many other species can’t.

Like all species, including humans, bacteria need water to help them break down or digest food. But bacteria can also break down fossil fuels, which are oils, and oil and water don’t mix together. So how do these bacteria manage to use water to help them digest oils anyway?

Normally, water molecules like to stick together, which results in oil being pushed out, keeping the two liquids separated. This happens because the structure of a water molecule gives it a negative charge on one side and a positive charge on the other. (This is what is known as a “polar” molecule.) That means one water molecule’s positive end likes to stick to the neighboring molecule’s negative end, making water cling together like a pack of weak magnets. As a result, oil (a non-polar molecule) gets pushed out and stays separated from water.

Some bacteria make special molecules called surfactants that help them pry water molecules apart, so that water can mix more easily with other substances. These special molecules have one end that is attracted to water (also known as hydrophilic, or “water-loving”) and one end that is repelled by water (hydrophobic, or “water-fearing”). So, while one end of a surfactant molecule attaches to a water molecule, the other end of the surfactant pushes other water molecules away. The result is that water no longer sticks together as well. This enables other substances like oil to fill in the spaces and come in closer contact with water. Two liquids which previously didn’t mix all of a sudden can mix together. Once mixed together in water, bacteria can begin to digest or break down the oil into simpler molecules and atoms, like hydrogen and carbon (the component parts of oils).

The actinobacteria are a large class of bacteria that includes 54 known families. They are able to make many different kinds of surfactants. Actinobacteria produce surfactant molecules having different shapes, sizes, and chemical behaviors. All of these different qualities make these surfactants behave slightly differently and enable the actinobacteria to digest many different oil-based food sources. Molecular methods of changing how oil is distributed can help people clean up wildlife and the environment in the case of oil spills. Bacterial surfactants were used to help clean up the Exxon Valdez oil spill, for example, and have been shown to clean shorelines contaminated with spilled oil. These surfactants are not only effective at breaking down oil, but are also biodegradable themselves, becoming a harmless part of the environment after use.

Secretion Solubilizes Oils and Water

Cladosporium resinae

Compounds secreted by Cladosporium resinae act as surfactants by self-assembling into a wide variety of 3-D configurations tailor-made for different circumstances when water and oil need to mix.

Last Updated May 14, 2020

References

“The combinations of different types of hydrophilic and hydrophobic moieties within surfactants are innumerable and highly biodiverse. Due to their amphiphillic structures, surfactants act as emulsifying agents, resulting in low surface tensions of interphases. Often, microorganisms produce them when growing on hydrophobic carbon sources or when exposed to growth limiting conditions. It is hypothesized, that biosurfactants play a role in the uptake of various hydrophobic carbon sources thus making nutrients bioavailable” (Kugler et al. 2015:1)

Journal article

Surfactants tailored by the class Actinobacteria

Frontiers in Microbiology, 6(212): 1-23 | 19/03/2015 | Kügler JH, Le Roes-Hill M, Syldatk C, Hausmann R

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Reference

“Many prokaryotic and eukaryotic microorganisms can grow on compounds that are poorly soluble in aqueous media. The growth on such substrates, like hydrocarbons, is often associated with the production of surface-active compounds. Surface-active molecules contain hydrophilic and hydrophobic moieties which enable them to concentrate at interfaces and to reduce the surface tensions of aqueous media.” (Christova et al. 2004:70)

Journal article

Rhamnolipid Biosurfactants Produced by Renibacterium salmoninarum 27BN During Growth on n-Hexadecane

Zeitschrift für Naturforschung C, 59(1-2): 70–74 | 01/02/2004 | Christova N, Tuleva B, Lalchev Z, Jordanova A, Jordanov B

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