MICROBIAL-METABOLISM OF XENOBIOTICS - FUNDAMENTAL AND APPLIED-RESEARCH

The ability of microorganisms to metabolise xenobiotic compounds has r eceived much attention due to the environmental persistence and toxici ty of these chemicals. The microbial degradation of xenobiotics is see n as a cost effective method of removing these pollutants from the env ironment by a process now known as bioremediation. Microbial treatment of industrial effluents is also possible. Fundamental work has reveal ed that a wide variety of microorganisms are capable of degrading an e qually wide range of organic pollutants. Pure and mixed cultures of mi croorganisms have been studied and degradation is observed under both aerobic and anaerobic conditions. Breakdown products have been found d uring work on the degradative pathways involved and toxicological asse ssments using bacteria and higher organisms (fish, plants) have been u sed to determine the toxicity of these intermediates. Many of the degr adative genes responsible for xenobiotic metabolism are present on pla smids, transposons or are grouped in clusters on chromosomes. This pro vides clues to the evolution of degradative pathways and makes the tas k of genetic manipulation easier such that new microbial strains capab le of efficiently degrading pollutants can be developed. Several enzym es involved in xenobiotic metabolism have been isolated and factors af fecting their activity investigated. Genetically manipulated strains o r naturally isolated organisms may be used in the treatment of industr ial wastes or as inocula to enhance degradation in the environment. En vironmental factors, including pH, temperature, bioavailability, nutri ent supply and oxygen availability have been shown to affect xenobioti c biodegradation. These factors must be optimised to obtain a satisfac tory microbial treatment process. Using information gained from fundam ental research, bioremediation technology has been used to detoxify di fferent contaminated environments and the results of field studies are very encouraging.