Environmental pollution is “the contamination of the physical and biological components of the earth/atmosphere system to such an extent that normal environmental processes are adversely affected”.

India has been ranked as seventh most environmentally hazardous country in the world by a new ranking released recently. The study is based on evaluation of “absolute” environment impact of 179 countries (Harvard, Princeton, Adelaide University and University of Singapore, 2011).

Thousands of hazardous waste sites have been generated worldwide resulting from the accumulation of xenobiotics in soil and water over the years (Jain, 2005). Xenobiotic compounds are human made chemicals that are present in the environment at unnaturally high concentrations. The word “xeno” means foreign. A compound that is normal to one organism may be a xenobiotic to another. Xenobiotic is a chemical which is found in an organism but which is not normally produced or expected to be present in it.

It can also cover substances which are present in much higher concentrations than are usual. Specifically, drugs such as antibiotics are xenobiotics in humans because the human body does not produce them itself nor would they be expected to be present as part of a normal diet. Organs transplanted in foreign bodies of different species are termed as xenotransplantation. However, the term is also used in the context of pollutants such as dyes, dioxins and polychlorinated biphenyls and their effect on the biota.

Natural compounds can also become xenobiotics if they are taken up by another organism (e.g., uptake of natural human hormones by fish found downstream of sewage treatment plant outfalls). There are two types of xenobiotic compounds. They may be biodegradable or non degradable /recalcitrant. Biodegradable xenobiotic compounds are those that get degraded by the action of microbes or other reactions while recalcitrant compounds are resistant to degradation by any reactions. The recalcitrant xenobiotic compounds can be grouped into various groups like halocarbons, polychlorinated biphenyls, oil mixtures, synthetic polymers, alkyl benzyl sulphonates, etc.

The potential health hazard of a xenobiotic compound is a function of its persistence in the environment as well as the toxicity of the chemical class. They tend to accumulate in the environment and lead to bioaccumulation and biomagnifications (Aelion et al., 1987). Biodegradation is considered as a phenomenon of biological transformation of organic compounds by living organisms particularly microbes. Biodegradation can be divided into three categories i.e. Mineralization, Biotransformation and Co-metabolism. Mineralization is a process where the organic chemical is broken down into inorganic compounds. It is also known as “ultimate biodegradation”.

Typical products of aerobic mineralization are carbon dioxide, water and ammonia. In biotransformation, the organic chemical only undergoes small structural changes. Co-metabolism is the transformation of a non-growth substrate in the obligate presence of a growth substrate or another transformable compound. Bioremediation is one of the efficient methods of remediation of organic pollutants / xenobiotics, as it is less expensive and can selectively achieve complete destruction of organic pollutants (Alexander, 1994; Cookson, 1995). Bioremediation can be defined as the action of microbes or other biological systems to degrade environmental pollutants.

Microorganism has the capability of degrading all naturally occurring compounds; this is known as the principle of microbial infallibility proposed by Alexander in 1965. Mix cultures of microbes can together be used to degrade xenobiotic compounds completely because they produce different enzymes that act on recalcitrant compounds and degrade them to simpler form. Smaller compounds are again taken up by other series of microbes and degraded wholly. Since xenobiotics consist of a wide variety of compounds, their degradation occurs via a large number of metabolic pathways. Degradation of alkanes and aromatic hydrocarbons generally occurs as follows: an oxygenase first introduces a hydroxyl group to make the compound reactive, the hydroxyl group is then oxidized to a carboxyl group, the ring structure is opened up (in case of cyclic compounds), the linear molecule is degraded by β-oxidation to yield acetyl CoA, which is metabolised in the usual manner.

Dyes and phenol are such xenobiotic compounds which accumulate in environment after being produced from various industrial operations. Textile dyes are one of the most prevalent type chemicals used today. Textile industry is the single largest organized sector in the country, employing almost 25% of the country’s labour force. India textile industry largely depends upon the textile manufacturing and export. It also plays a major role in the economy of the country. It account for almost 1/3rd of the total export earning in the country (Juwarkar et al., 1997; Paul, 1997).

Further, the textile industry of India also contributes nearly 14% of the total industrial production and 3% to the GDP of the country (Annual Report 2009-10, Ministry of Textiles). The industry is expected to grow from the present US$ 70 billion to US$ 220 billion by 2020. The total cloth production has increased by 2.9 per cent during December 2010 as compared to December 2009. Biodegradation is considered as a phenomenon of biological transformation of organic compounds by living organisms particularly microbes.

Biodegradation can be divided into three categories i.e. Mineralization, Biotransformation and Co-metabolism. Mineralization is a process where the organic chemical is broken down into inorganic compounds. It is also known as “ultimate biodegradation”. Typical products of aerobic mineralization are carbon dioxide, water and ammonia. In biotransformation, the organic chemical only undergoes small structural changes. Co-metabolism is the transformation of a non-growth substrate in the obligate presence of a growth substrate or another transformable compound. Bioremediation is one of the efficient methods of remediation of organic pollutants / xenobiotics, as it is less expensive and can selectively achieve complete destruction of organic pollutants (Alexander, 1994; Cookson, 1995).

Bioremediation can be defined as the action of microbes or other biological systems to degrade environmental pollutants. Microorganism has the capability of degrading all naturally occurring compounds; this is known as the principle of microbial infallibility proposed by Alexander in 1965. Mix cultures of microbes can together be used to degrade xenobiotic compounds completely because they produce different enzymes that act on recalcitrant compounds and degrade them to simpler form. Smaller compounds are again taken up by other series of microbes and degraded wholly. Since xenobiotics consist of a wide variety of compounds, their degradation occurs via a large number of metabolic pathways.

 Degradation of alkanes and aromatic hydrocarbons generally occurs as follows: an oxygenase first introduces a hydroxyl group to make the compound reactive, the hydroxyl group is then oxidized to a carboxyl group, the ring structure is opened up (in case of cyclic compounds), the linear molecule is degraded by β-oxidation to yield acetyl CoA, which is metabolised in the usual manner.