ABSTRACT
An attempt is made to describe the various pathways used by microorganisms to degrade or transform a wide range of xenobiotics. Attention has been directed to the various pathways that may be used by different organisms for the degradation of a given xenobiotic. Quite extensive investigations have been directed to the biodegradation of heterocyclic aromatic compounds, since a number of these are constituents of crude oil and creosote. Some examples are given of a few biotransformation reactions that may be relevant to biotechnology and of the environmental significance of the biotransformations of xenobiotics which result in metabolites more toxic than their precursors. Fungal metabolism of polycyclic aromatic hydrocarbons has been studied particularly extensively with Cuninghamella elegans. The metabolism of 1,3,5-triazine herbicides containing chlorine substituents also involves hydrolytic displacement of chloride. In contrast to the situation with fungi, bacteria may grow at the sole expense of polycyclic aromatic hydrocarbons; ring cleavage takes place after dioxygenation and dehydrogenation.
