biodegrade xenobiotic compounds , Biology

Xenobiotic compounds are man-made chemicals that are present in the environment at unnaturally high concentrations. The xenobiotic compounds are either not produced naturally, or are produced at much lower concentrations than man. Micro-organism have the capability of degrading all naturally occurring compounds; this is known as the principle of microbial infallibility proposed by Alexander in 1965. Micro-organisms are also able to degrade many others. The compounds that resist  biodegradation and thereby persist in the environment are called recalcitrant. The xenobiotic compounds may be recalcitrant due to one or more of the following reasons: (i) they are not recognized as substrate by the existing degradative enzymes, (ii) they are highly stable, i.e. chemically and biologically inert due to the presence of substitution groups like halogens, nitro-, sulphonate, amino-.methoxy- and carbamyl groups, (iii) they are insoluble in water, or are adsorbed to external matrices like soil, (iv) they are highly toxic or give rise to toxic products due to microbial activity, (v) their large molecular size prevents entry into microbial cells, (vi) inability of the compounds to induce the synthesis of degrading enzymes, and (vii) lack of the permease needed for their transport into the microbial cells.

Types of recalcitrant xenobiotic compounds

The recalcitrant compounds can be grouped into the following 6 types: (i) halocarbons, (ii) polychlorinated biophenyls, (iii) synthetic polymers, (iv) alkylbenzyl sulphonates, (v) oil mixture and (vi) others. The structural features that make these compounds resistant to microbial degradation include the following: (i) presence of halogens in the place of hydrogen in the molecule; the carbon-halogen bond is highly stable and its cleavage requires considerable energy, (ii) substitution of H by other groups like nitro-, sulphonate, methoxy-, amino- and carbomyl groups, (iii) cyclic structures, aromatic compounds, cycloalkanes and heterocyclic compounds are more recalcitrant than linear chain or aliphatic compounds, (iv) branched linear chains resist biodegradation etc. In general, the more complex is the structure of a xenobiotic compound, the more resistant it is to biodegradation. Many other xenobiotics resist biodegradation due to their large molecular size and insolubility in water.

Hazards from xenobiotics

A number of pesticides are based on aliphatic, cyclic ring structures containing substitution of nitro-, sulphonate, methoxy-, amino- and carbomyl groups; in addition, they also contain halogens. These substitutions make them recalcitrant.

The xenobiotics present a number of potential hazards to man and the environment which are briefly listed below:

1. Toxicity: Many xenobiotics like halogenated and aromatic hydrocarbons are toxic to bacteria, lower eukaryotes and even humans. At low concentrations they may cause various skin problems and reduce reproductive potential.

2. Carcinogenicity: Certain halogenated hydrocarbons have been shown to be carcinogenic.

3. Many xenobiotics are recalcitrant and persist in the environment so that there is a buildup in their concentrations with time.

4. Many xenobiotics including DDT and PCB's are recalcitrant and lipophilic; as a consequence they show bioaccumulation or biomagnifications often by a factor of 104 - 106. Biomagnifications occurs mainly taken up from the two reasons: (i) these compounds are continuously taken up from the environment and accumulated in the lipid deposits of body, e.g. a 100-fold accumulation of DDT by plankton from water. (ii) such organisms are consumed by other organism in a sequential manner constituting the food chain.

Posted Date: 8/20/2012 5:04:39 PM | Location : United States

Related Discussions:- biodegrade xenobiotic compounds , Assignment Help, Ask Question on biodegrade xenobiotic compounds , Get Answer, Expert's Help, biodegrade xenobiotic compounds Discussions

Write discussion on biodegrade xenobiotic compounds
Your posts are moderated
Related Questions
The fundamental contractile unit is the sarcomere. Each muscle cell apart from the nucleus, mitochondria and other structures contains parallel fibrils. Sarcomere is a subunit of t

Selenium Glutathione peroxidase (GSH-Px) was the first selenium metalloenzyme identified.Glutathione peroxidase catalyzes the reduction of hydrogen peroxide and lipid h yp r o

ERRORS IN FERTILIZATION  - 1.       Polyspermy - When more than one sperms are fused in an ovum, this condition is called polyspermy. 2.       Polygynae - During oogen

Embryology This is the study of growth, fertilization, division or differential of the zygote into embryo of early development of living beings before the attainment of structure

Why do scientists make biological collections? What are the scientific reasons for doing a collection? How is a collection done?

What is an argument that shows that the emergence of photosynthetic beings was crucial for life to reach the marine surface and later the dry land? The Ultraviolet radiation fr

What are fossil fuels? Fossil fuels, like oil, gas and coal, form when organic material is preserved from the complete action of decomposers, generally buried deep and under pr

Define Key Concepts and Facts of Polysaccharides? 1. All polysaccharides contain several monosaccharide units. 2. All monosaccharide units are joined to each other by glycosidi

Explain the Sticky Films - Food Microbiology? Sticky films or tape are pressed against the surface to be assessed. Exposed film/tape is then pressed on the agar plate and analy

Contemporary Interests in Nutritional Biochemistry As  newer techniques in biochemistry have emerged from time to time, these were of immense help  in  the  understanding of ut