Training Manual Application of Genetics and Biotechnology in ...

greatly improves water quality and reduces the pollution level of wastewater before
its release into the environment.
Bioremediation techniques were first pioneered by the petroleum industry (Soli
and Bens, 1972) and have become a popular alternative to chemical or physical
remediation because of their relatively 'low cost and minimal impact on the
environment. The interactions between bacteria and pollutant occur through complex
biochemical and chemical reactions. During the process, micro-organisms, usually
bacteria, feed on the contaminants and they provide enzymes to enhance
mineralization of organic matter and to convert toxic complex molecules into water
and carbon dioxide or other harmless smaller molecules. Bioremediation has many
other advantages such as improving immunity of cultured animals to pathogenic
micro-organisms. In addition, beneficial bacteria competitively exclude pathogenic
bacteria or produce substances that inhibit the growth of the pathogenic bacteria and
prevent the level of infection and frequent outbreaks of diseases. They provide
essential nutrients to enhance the nutrition of the cultured animals and also digestive
enzymes to enhance the digestion of the cultured animals. Hence, bioremediation is a
constructive approach for decontamination of various toxicants and this can provide a
low cost alternative to other remediation techniques. Moreover, it is becoming
evident that indigenous microbial populations rather than introduced populations may
be ecologically superior for use in natural systems. In situations where indigenous
degraders cannot rapidly degrade recalcitrant chemicals, bioaugmentation may be the
only means of successful bioremediation.
Several mechanisms which would account for the acclimatization of
microbial communities in polluted environments have been proposed: a) Induction of
specific enzymes not present in populations before exposure to the toxicant. b)
Genetic selection for new metabolic abilities c) Increase in the number of microbes
that are able to transform. the toxicant to a less toxic form d) Chemical structure of
the pollutant. The adaption of microbial communities to pollutants results in the
enhancement of biodegradation and the development of resistance to these noxious
substances (Barkay and Pritchard, 1988).