After reading this article you will learn about microbial degradation of oil and petrochemicals in the sea.
A variety of microorganisms capable of growing on oil have been isolated from the marine environment. About 191 strains belonging to the genera Pseudomonas, Achromobacter, Acinetobacter, Arthrobacter, Flavobacteria, & Brevibacteria were isolated from sea water near coastal oil discharge sources.
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Several effective fungal strains were also isolated from sea water—these include Cunninghamella elegans, Aspergillus versicolor, Cephalosporium Sp., Acremonium Sp. and Penicillium Sp. These fungi could grow on a wide range of hydrocarbon substracts.
As soon as oil enters the sea it becomes contaminated with a variety of microorganisms, a number of which can grow on the oil and its degradation products. Most workers consider that bacteria are by far the most important microorganisms involved in oil biodegradation in the sea.
In the laboratory, several strains of Pseudomonas, Achromobacter, Flavobacterium were tested for their oil biodegradation efficiency. In the seawater and sediments of oil polluted areas, the frequency of the hydrocarbons oxidising bacteria were very much (108 – 109/ml of water or mud).
Microbially infected oils may undergo marked modifications in their chemical composition. The rate at which such changes occur in the sea is influenced by certain environmental factors (viz., water temperature, oxygen, nitrogen and phosphorus content of water) and also by the initial composition of the oil.
Crude oil contains 90 – 99% of hydrocarbons, the remainder comprising compounds containing sulphur, oxygen and nitrogen and also trace amounts of metals. Microorganisms can attack most hydrocarbons found in crude oils and elsewhere. The rate of biodegradation of oil at sea is highly variable, which depends on number of factors.
The microbial flora in the oil film and oil deposits of the bottom are also rich in sulphate-reducing and denitrifying anerobic bacteria and sulphur oxidising aerolic bacteria like Thiobacillus.
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Phenolic wastes are admittedly the most serious pollutants of oil refineries because even minute amounts of their chlorinated derivatives input objectionable taste and odour to drinking water. Several laboratories and companies established a number of microbial methods for disposal of such wastes.
The reaction leading to the decomposition of such wastes is:
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A number of bacteria viz. Bacillus subtilis, B. megaterium, E. coli, Chromobacter sp are quite efficient in phenol degradation. Thus disposal of refinery and oil field wastes into the river or sea needs proper microbial treatment for control of oil pollution into the sea.
In this context it is worthwhile to note the fact that the first engineered microorganisms with advanced degradative properties were generated by Dr. Ananda Mohan Chakravorty and his colleagues in the 1970s. Plasmids were transferred into a bacterial strain that could degrade several compounds in petroleum. Subsequently Dr. Chakravorty obtained the first US patent for a genetically engineered microorganism.
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Metallic Pollutant and Aquatic Biota of the Sea:
A large number of metallic pollutant are released into the sea through various kinds of effluent discharges. Among them chromium, cadmium, mercury, lead, copper, zinc, nickel, silver, etc. are very important. Most of these trace metals have tremendous effects on the growth and development of aquatic biota.
At sub-lethal concentration of metallic pollutant there are three kinds of reaction that takes place. Many organisms possess the ability to detect high levels of these pollutants in solution in the ambient aquatic environment. They maintain an avoidance reaction to overcome the pollution toxicity.
Pollutant induced physiological changes may also be adjusted by some organisms. The predator-prey relationships may, however, be disturbed very much even at lower concentrations of trace metals. Trace metal toxicity is very much pronounced in phytoplankton’s, macro-algae, molluscs, echinoderms, crustaceans, and finfish.