Micro-organisms are known to use several substrates as their source of energy and play a major role in the natural degradation processes that take place around us. This helps to break down the waste materials and convert it into less toxic forms which will mostly be in sync with the environment. This process is generally termed as biodegradation. Bioremediation is defined as the process in which microbes are deliberately used to clean up the environment and degrade waste or chemicals that are hazardous to the environment and can affect the different life forms in the immediate ecosystem.
Oil spill occurs due to the intentional or unintentional release of petroleum hydrocarbons of any form into the environment due to human activity. It is considered as a form of pollution and often refers to oil spills in marine ecosystem or coastal areas. The spill can originate from oil tankers, off-shore platforms, oil rigs and even the heavier fuels and refined petroleum products add to the list. There have been many cases of oil spills all over the world since the 1950's and the after effects of it were terrifying. It mainly affects the birds and sea mammals which lose their ability of temperature tolerance due to oil coatings on their body and cause dehydration and digestion problems due to accidental intake of oil. The marine plants are also affected because of reduced sun light penetration caused by the top oil layer on the surface of water, which affects photosynthesis.
Usually the exposure of crude oil in the environment automatically attracts oil degrading microbes to the area and the biodegradation process does occur, but takes a long time to clear off the mess, and by that time it would do extensive damage to the surrounding life forms, including humans who consume the fish from the ocean polluted by oil spill. Bioremediation was proposed even much earlier to help clean up oil spills, but people didn't have much knowledge about the process at that time, and there were no experimental evidences to prove its quick action and better efficiency. Now we know that there are large number of microbes that can break down oil through a special metabolic pathway to form carbon dioxide and fatty acids as by products.
In bioremediation, the natural biodegradation action is speeded up by either introducing exogenous microbial population, or stimulating the indigenous microbial population by providing favourable growth conditions like optimum temperature, nutrients, aeration, etc. The Pseudomonas species is commonly used for oil degradation. The invention of the 'super bug' Pseudomonas putida, a gram negative rod shaped soil bacteria by Ananda Mohan Chakrabarty has the capability of cleaning up about three-fourth of the oil pollution. The super bug is a genetically engineered organism whose plasmid contains the genes responsible for oil degradation from four different species of bacteria and is the first living organism to be patented.
The method of adding a set of microbes to the affected area is called seeding. The microbes used for seeding is usually got from the enrichment cultures from previous affected sites. Even genetically engineered organisms can be used in this method to enhance the clean-up. However, it is seen that the added culture of micro-organisms are less effective when compared to the oil eating microbes naturally present in the polluted zone. This led to another approach of bioremediation through the environmental modification. There are various rate limiting factors that affect the growth and activity of oil degraders. The activity is less or negligible in anaerobic regions because most of the microbes need oxygen for executing the first step of degradation process. So, supplying molecular oxygen and certain essential nutrients like nitrogen and phosphorus can help to stimulate the organism to grow on oil at a faster rate.
The wide field study conducted showed positive results about the higher rate of oil degradation at polluted sites by natural population of microbes. The addition of fertilizers is considered safe, but its effect depends on environmental factors like temperature, substrate and water run off which are not yet fully understood. Still, bioremediation is considered as the most reliable and quick way of treating oil spills. The speedy clean-up can not only save the environment and living organisms, but also have other advantages like reducing economic impacts, handling legal liabilities and settlement of claims.
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