Bacteria and the Biodegradation of Chemicals Achieved Naturally, by Combination, or by Construction

The natural potential of bacteria for the biological degradation of synthetic compounds is greater than is commonly supposed and extends to many heteroarenes and even some chloroarenes. An increase in the number of substituents on the aromatic ring or a certain substitution pattern is what confers xenobiotic character to a compound. In addition, when enzymes with low substrate specificity encounter foreign compounds with random variations, products with very strong xenobiotic character often result. In this case, changing the conditions or introducing a cooperation between several different types of bacteria can be used to degrade these compounds. Finally, mineralization, the complete breakdown of organic substances into carbon dioxide and inorganic salts, of xenobiotics previously regarded as persistent can be achieved by taking advantage of natural or induced gene transfer to construct hybrid degradative pathways. After an introduction to the world of bacteria and their place in Nature, we will describe their natural potential for biodegradation with reference to aliphatic and aromatic hydrocarbons. The discussion will then turn to the types of the substituents that confer xenobiotic properties to compounds and how these compounds are degraded despite their xenobiotic character.