There have been many cases of oil spillage near oil rigs.Nowadays microorganisms used in cleaning up of oil spills are those bacterial organisms which grow on alkenes , butanes and hydrocarbons .This type of bacteria is like automobiles which use hydrocarbons, to chew out harmless carbon dioxide and water.” Alcanivorax borkumensis ” is a common examples of microbes that utilize hydrocarbons to produce secondary metabolites.These type of microorganisms are generally genetically modified to work on oil to produce fat globules which can easily be dissolved in water .
This type of microorganisms produce bio surfactants like glycolipids, heteropolysaccharides, phospholipids, surface active antibiotics like Gramicidin, Surfactin and TA which also reduce surface tension and help in fast digestion of alkanes and butanes into fat globules and lipids.A. borkumensis is found naturally in seawater environments.It is common in oceanic areas containing petroleum oil (whether from spills, natural fields, or other sources).It can also be found in small amounts of unpolluted water.It has been found across the world in various locations both in coastal environments and oceanic environments.It can also flourish in areas with heavy tides and other sea related currents/flow. It is found only on or near the surface of water. A. borkumensis can live in waters with salinities ranging from 1.0-12.5% and temperatures ranging from 4-35 °C.A. borkumensis outcompetes other species of the Alcanivorax genus, due to its highly flexible DNA and metabolism.A. borkumensis also outcompetes other alkane-degrading organisms such as Acinetobacter venetianus. A. borkumensis can consume a wider variety of alkanes.
Some other type of microorganisms used commercially to treat oil spills are :
- Haloanaerobium acetoethylicum
- H. congolense
- H. salsugo
Mesophilic fermentation bacteria are more common than the thermophilic ones. The first group comprises of haloanaerobes such as Haloanaerobium acetoethylicum,H.congolense, and H. salsugo that produces acetate or ethanol in the process of carbohydrate fermentation. These microorganisms differ in the type of substrates used and their tolerance to salt content (up to 10 %).
For example, Spirochaeta smaragdinae isolated from a Congo oil field, prefers salt contents of up to 5 %. The same source, however, yields Dethiosulfovibrio peptidovarans with specific metabolism as well. This bacteria has the ability to biodegrade protein extracts and the products of its metabolism into organic acids such as:
- 2-methylbutyric acids
Spirochaeta smaragdinae also has the ability to reduce thiosulfate and prefers salt contents up to 3 % of NaCl .
Mechanism of Hydrocarbonoclastic Bacteria ( HCB ) in Oil Spills Treatment
A. borkumensis primarily uses alkanes as its source of energy/carbon, but it also can use a some other organic compounds. Unlike most other cells, it cannot consume common substances such as sugars or amino acids as a source of energy.
To increase the growth rate of a population of A. borkumensis bacteria, phosphorus and nitrogenous compounds can be added to the environment. These substances act as a fertilizer for the bacteria and help them grow at an increased rate .
A. borkumensis and Bio-surfactants
When A. borkumensis bacteria uses alkanes as its source of energy, each cell forms a bio-surfactant (other sources of energy do not cause this bacteria to produce this bio-surfactant). A bio-surfactant is an extra layer of material that forms along water cell membrane. The substances that make up the biosurfactant of A. borkumensis can reduce surface tension of water, which helps with the degradation of oil from oceans. They are also used as emulsifiers, which further convert the oilwater into emulsions, making oil more soluble in water. A. borkumensis forms a biofilm around all oil droplets in seawater and uses bio-surfactants and metabolism to degrade oil into a water-soluble substance .
Crude oil, or petroleum, is predominantly made up of hydrocarbons, a product that consists of a long chain of carbon atoms attached to hydrogen atoms. Most organisms use sugars or amino acids for their source of carbon/energy, A. borkumensis on the other hand 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. Along with flourishing in an oil spill,this bacteria helps in oil spill treatment as well.
Through its metabolism, A. borkumensis can break down oil into harmless compounds. This ability makes this particular species a major potential source for bioremediation of oil-polluted marine environments .