Alcanivorax borkumensis

Chromohalobacter
Scientific classification
Kingdom: Bacteria
Phylum: Proteobacteria
Class: Gamma Proteobacteria
Order: Oceanospirillales
Family: Alcanivoracaceae
Genus: Alcanivorax
Yakimov et al. 1998
Species: Borkumensis

Alcanivorax borkumensis is an alkane-degrading marine bacterium which naturally propagates and becomes predominant in crude-oil-containing seawater when nitrogen and phosphorus nutrients are supplemented. They are currently thought to be the world's most important oil-degrading organisms.[1][2]

Description

A. borkumensis is a rod shaped bacterium without flagella that obtains its energy primarily from eating alkanes (a type of hydrocarbon). It is aerobic, meaning it uses oxygen to gain energy, and it is halophilic, meaning it tends to form in environments that contain salt, such as salty ocean water. It is also gram-negative, which essentially means that it has a relatively thin cell wall. Gram negative is a term used to explain that this bacterium does not keep the purple stain from the classifying experiment Gram's Method. It is also non-motile, however, other organisms that appear to be in the same genus are motile through flagella.[3][4]

Genome

The genome of A. borkumensis is a single circular chromosome that contains 3,120,143 base pairs. It is highly adapted to degrading petroleum oil. For example, a certain sequence on the genome codes for the degradation of a certain range of alkanes. The A. borkumensis genome has many sequences that each code for a different type of alkane, allowing it to be highly adaptable and versatile. Its genome also contains instructions for the formation of biosurfactants which aid in the process of degradation. To deal with external threats, the A. borkumensis genome also codes for several defensive mechanisms. Coping with high concentrations of sodium ions (i.e. in ocean water), and protecting against the UV radiation experienced on the surface of the earth are both important for the A. borkumensis bacteria, whose genome contains ways to solve both of these problems.[5]

Ecology

A. borkumensis is found naturally in seawater environments. It is more common in oceanic areas containing petroleum oil (whether from spills, natural fields, or other sources), although it can be found in small amounts in non-polluted water. It has been found across the world in various locations both in coastal environments and oceanic environments. It also can flourish in areas with heavy tides and other sea related currents/flow. It is able to exist even when large amounts of solid matter (such as sand or gravel) exist nearby.[2] It is found only on or near the surface of water. A. borkumensis can live in salinities ranging from 1-12.5% and in temperatures ranging from 4-35°C.[4] The abundance of A. borkumensis in oil-affected environments is because the bacteria uses the compounds in oil as a source of energy, thus populations of A. borkumensis naturally flourish at oil spills or other similar locations. It has been observed that A. borkumensis outcompetes other species of the Alcanivorax genus, likely due to its highly flexible DNA and metabolism. A. borkumensis also outcompetes other alkane degrading organisms such as Acinetobacter venetianus. It was experimentally shown that, after a certain period of time, an oily and saline environment containing A. borkumensis and Acinetobacter venetianus would eventually become dominated by A. borkumensis. This is because A. borkumensis can consume a wider variety of alkanes than other known species.[6]

Metabolism

A. borkumensis primarily uses alkanes as its source of energy/carbon, however, there are a few other organic compounds that it can utilize. Unlike most other cells, it cannot consume more common substances such as sugars or amino acids as a source of energy.[4]

To increase the growth rate of a population of A. borkumensis bacteria, phosphorus and nitrogen can be added to the environment. These substances act as a fertilizer for the bacteria and help them grow at an increased rate. It should be noted that nitrogen makes up the largest percentage of earth’s atmosphere, making it readily available for surface dwelling bacteria like A. Borkumensis. Phosphorus is less naturally abundant, but can be produced in labs.[2]

A. Borkumensis and Biosurfactants

When A. borkumensis bacteria use alkanes as their source of energy, each cell forms a biosurfactant (other sources of energy do not cause the bacteria to produce this biosurfactant). A biosurfactant is an extra layer of material that forms along the cell membrane. The substances that make up the biosurfactant of A. borkumensis can reduce the surface tension of water, which helps with the degradation of oil. They are also emulsifiers, which further serve to break up the oil/water emulsion, making oil more soluble. A. borkumensis forms a biofilm (a wall of cells) around an oil droplet in seawater and proceeds to use biosurfactants and metabolism to degrade the oil into a water-soluble substance.[4]

Role in Oil Biodegradation

Petroleum oil is toxic for most life forms and pollution of the environment by oil causes major ecological problems. A considerable amount of petroleum oil entering the sea is eliminated by the microbial biodegradation activities of microbial communities. A. borkumensis is a recently discovered hydrocarbonoclastic bacterium and is probably the most important global oil degrader.[1] A. borkumensis is capable of degrading oil in seawater environments. It is known as a hydrocarbonoclastic organism, with the word ‘clastic’ meaning it can divide something into parts (in this case hydrocarbons). Crude oil, or petroleum, is predominantly made up of hydrocarbons, a product that consists of a long chain of carbon atoms that are subsequently attached to hydrogen atoms. Whereas most organisms use sugars or amino acids for their source of carbon/energy, A. borkumensis uses alkanes, a type of hydrocarbon, in its metabolic process. This diet allows A. borkumensis to flourish in marine environments that have been affected by oil spills. Through its metabolism, A. borkumensis can break down oil into harmless compounds. This ability makes this particular species of bacteria a major potential source for bioremediation of oil polluted marine environments.[2]

Potential as Anti-Oil Spill Agent

Currently, petroleum is the largest source of energy for humans on this planet. People are constantly looking to find new sources of oil, and some have tried drilling the bottom of the ocean to find new wells. Unfortunately, the drilling or transporting process can occasionally go awry, leading to severe ecological disasters called oil spills. Oil spills can occur during transportation of oil (see Exxon Valdez), or during the extraction (see BP oil spill). Such spills dump thousands of barrels of oil into the ocean and pollute the environment, affecting ecosystems near and far.

Normally, it would take many years for an ecosystem to recover fully (if at all) from an oil spill, so scientists have been looking into ways to expedite the clean up of areas affected by an oil spill. Most efforts so far utilize direct human involvement/labor to physically remove the oil from the environment. However A. borkumensis presents a possible alternative. Since A. borkumensis naturally breaks down oil molecules to a non-polluting state, it would greatly help ecosystems to quickly recover from an oil spill disaster. The organisms also naturally grow in oil-contaminated seawater, and are thus a native species. If the process that A. borkumensis uses to break down oil could be sped up or made more efficient, this would greatly aid recovering ecosystems. Some examples of ways to accomplish this task include encouraging the growth of A. borkumensis (through phosphorus and nitrogen fertilization) so that there are more of them breaking down oil, or encouraging the metabolism of A. borkumensis so that they eat faster and eat more.[2][6]

References

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and USA.gov, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for USA.gov and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
 
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
 
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.