Biodegradation of Xenobiotic Compounds involve the degradation of xenobiotic compounds by microorganisms. These compounds may be biodegradable , nonbiodegradable or highly recalcitrant. On the other hand biogenic compounds are naturally occurring so these can be easily a d almost completely biodegraded.
Mechanisms developed by microorganisms for biodegradation:
Following mechanisms are developed by microorganisms for the biodegradation of xenobiotic compounds.
- Gratuitous metabolism,
- Mixed microbial populations,
- Natural recombination,
- Genetic engineering,
- Natural mutation.
Co metabolism is simultaneous degradation of two compounds in which the degradation of second compound depends upon the presence of the first compound.
For example; mycobacterium vaccae oxidises ethane or propane, as a result the enzyme propane oxygenase is produced, which in turn degrades cyclohexane. In co-metabolism, the xenobiotic compounds are not used as energy source. In this case energy is obtained from the propane or ethane.
- Gratuitous metabolism:
In gratuitous metabolism, xenobiotic compounds are degraded by microorganisms using their existing pathways and these xenobiotic compounds are used as a source of energy. The xenobiotic compounds may be completely or partially degraded, whatever is the degradation but the product will be less toxic.
- Mixed microbial population:
The phenomena of use of mixed microbial cultures having different degrading probabilities is called bioaugmentation.
There are two reasons why bioaugmentation is preferred; first, if two different microorganisms are present, they have synergistic effect to degrade xenobiotic compounds completely. If acting alone, they will be incapable of degrading. Second, mixed microbial cultures provide nutrients requirement to each other.
- Natural recombination:
This is a phenomenon where plasmids with novel characteristics are transferred from one organism to another. Plasmid transfer can enhance xenobiotic degradation capabilities of microorganisms. Also, novel microorganisms can be produced by this method.
- Genetic engineering:
Genetic engineering of microorganisms involves producing genetically engineered microorganisms which initially could not degrade xenobiotic compounds but now can. Here, either new set of genes coding different enzymes are produced or regulatory element is modified to enhance enzyme synthesis. Both of these can be used to enhance the biodegradation property of microorganisms.
- Natural mutation:
Gene mutation occurs spontaneously in these microorganisms because they have very short generation time and very large population. So mutation becomes very potent source of variation. Mutation modify the active site of enzyme, so that it has increased activity for xenobiotic compounds
Mutation can eliminate the regulatory control for enzyme synthesis. It enhance degradation of xenobiotic compounds but new enzyme is not synthesized. 1/1000 cells are mutants, if capacity to degrade increases, then this cell is desired mutant.
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