MICROBIAL-METABOLISM OF PYRIDINE, QUINOLINE, ACRIDINE, AND THEIR DERIVATIVES UNDER AEROBIC AND ANAEROBIC CONDITIONS

Our review of the metabolic pathways of pyridines and aza-arenes showe d that biodegradation of heterocyclic aromatic compounds occurs under both aerobic and anaerobic conditions. Depending upon the environmenta l conditions, different types of bacteria, fungi, and enzymes are invo lved in the degradation process of these compounds. Our review indicat ed that different organisms are using different pathways to biotransfo rm a substrate. Our review also showed that the transformation rate of the pyridine derivatives is dependent on the substituents. For exampl e, pyridine carboxylic acids have the highest transformation rate foll owed by monohydroxypyridines, methylypridines, aminopyridines, and hal ogenated pyridines. Through the isolation of metabolites, it was possi ble to demonstrate the mineralization pathway of various heterocyclic aromatic compounds. By using C-14-labeled substrates, it was possible to show that ring fission of a specific heterocyclic compound occurs a t a specific position of the ring. Furthermore, many researchers have been able to isolate and characterize the microorganisms or even the e nzymes involved in the transformation of these compounds or their deri vatives. In studies involving O-18 labeling as well as the use of cofa ctors and coenzymes, it was possible to prove that specific enzymes (e .g., mono- or dioxygenases) are involved in a particular degradation s tep. By using (H2O)-O-18, it could be shown that in certain transforma tion reactions, the oxygen was derived from water and that therefore t hese reactions might also occur under anaerobic conditions.