Bioaugmentation in Wastewater Treatment Plants for Degradation of Xenobiotics

In biotechnology and pharmacology, mutants of bacteria or fungi or genetically engineered organisms are widely used in the production of citric acid, gluconic acid, as-corbate, and pharmaceuticals such as penicillin, insulin, and blood coagulation factors. Bacteria and fungi have also been adapted or genetically transformed for soil remediation (Atlas, 1981; Margesin and Schinner, 1997, Korda et al., 1997; Megharai et al., 1997). For wastewater and sludge stabilization however, successful use of genetically modified bacteria or of bacteria that can serve as donors for plasmids encoding degradative enzymes has been rather rare (van Limbergen et al., 1998). Usually, natural selection of the most suitable microorganisms from a complex flora, simply by adapting process parameters, is used. The limited reports on successful bioengineering for wastewater treatment may result from any of several factors: • The plasmids were unstable or the genes are not expressed in the new environ-

• Inoculated strains did not survive or, if they survived, metabolic activity was too low for successful competition with autochthonous strains.

• Inoculated strains, serving as a gene source, survived, but other strains were not competent for gene transfer.

• Wastewaters normally contain a complex spectrum of carbon sources that are better than xenobiotics, and so organisms do not express genes for degrading xenobiotics.

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