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22.5C: Prokaryotes and Environmental Bioremediation

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    Bioremediation occurs when prokaryotes clean up a polluted environment through the natural breakdown of pollutants.

    Learning Objectives
    • Give examples of the use of prokaryotes in enviromental bioremediation

    Key Points

    • To clean up oil spills, bacteria are introduced to the area of the spill where they break down the hydrocarbons of the oil into carbon dioxide; this is an example of bioremediation.
    • Toxic metals, such as mercury (II), can be converted into nontoxic forms, such as mercury (0), by bacteria.
    • Using natural organisms as examples, scientists can engineer bacteria for improved bioremediation of desired pollutants.
    • Bioremediation can remove oil, some pesticides, fertilizers, and toxic chemicals, such as arsenic, from the environment.

    Key Terms

    • bioremediation: the use of biological organisms, usually microorganisms, to remove contaminants, especially from soil or polluted water
    • biotransformation: the changes (both chemical and physical) that occur to a substance (especially a drug) by the actions of enzymes within an organism

    Using Prokaryotes to Clean up Our Planet: Bioremediation

    Microbial bioremediation is the use of prokaryotes (or microbial metabolism) to remove pollutants. Bioremediation has been used to remove agricultural chemicals (pesticides, fertilizers) that leach from soil into groundwater and the subsurface. Certain toxic metals and oxides, such as selenium and arsenic compounds, can also be removed from water by bioremediation. The reduction of SeO4-2 to SeO3-2 and to Se0 (metallic selenium) is a method used to remove selenium ions from water. Mercury is an example of a toxic metal that can be removed from an environment by bioremediation. As an active ingredient of some pesticides, mercury is used in industry and is also a by-product of certain processes, such as battery production. Methyl mercury is usually present in very low concentrations in natural environments, but it is highly toxic because it accumulates in living tissues. Several species of bacteria can carry out the biotransformation of toxic mercury into nontoxic forms. These bacteria, such as Pseudomonas aeruginosa, can convert Hg+2 into elemental Hg0, which is nontoxic to humans.

    One of the most useful and interesting examples of the use of prokaryotes for bioremediation purposes is the cleanup of oil spills. The importance of prokaryotes to petroleum bioremediation has been demonstrated in several oil spills in recent years, such as the Exxon Valdez spill in Alaska (1989), the Prestige oil spill in Spain (2002), the spill into the Mediterranean from a Lebanon power plant (2006), and, more recently, the BP oil spill in the Gulf of Mexico (2010). To clean up these spills, bioremediation is promoted by the addition of inorganic nutrients that help bacteria to grow. Hydrocarbon-degrading bacteria feed on hydrocarbons in the oil droplet, breaking down the hydrocarbons. Some species, such as Alcanivorax borkumensis, produce surfactants that solubilize the oil, whereas other bacteria degrade the oil into carbon dioxide. In the case of oil spills in the ocean, ongoing, natural bioremediation tends to occur if there are oil-consuming bacteria in the ocean prior to the spill. In addition to naturally occurring oil-degrading bacteria, humans select and engineer bacteria that possess the same capability with increased efficacy and the spectrum of hydrocarbon compounds that can be processed. Under ideal conditions, it has been reported that up to 80 percent of the non-volatile components in oil can be degraded within one year of the spill. Other oil fractions containing aromatic and highly-branched hydrocarbon chains are more difficult to remove and remain in the environment for longer periods of time.

    image
    Figure \(\PageIndex{1}\): Bioremediation in the Exxon Valdez oil spill: (a) Cleaning up oil after the Valdez spill in Alaska, workers hosed oil from beaches and then used a floating boom to corral the oil, which was finally skimmed from the water surface. Some species of bacteria are able to solubilize and degrade the oil. (b) One of the most catastrophic consequences of oil spills is the damage to fauna.

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    This page titled 22.5C: Prokaryotes and Environmental Bioremediation is shared under a CC BY-SA 4.0 license and was authored, remixed, and/or curated by Boundless.

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