EN
Polycyclic aromatic hydrocarbons (PAHs) are the compounds whose presence in contaminated soils and sediments poses a significant risk to the environment, they show also cytotoxic, mutagenic, and in some cases carcinogenic effects on human tissue. A wide range of different microorganisms in the soils are able to metabolize, cometabolize and utilize the PAHs as a sole source of carbon and energy. The aerobic catabolism of monocyclic and two-, threecyclic aromatic hydrocarbons by bacteria has been extensively studied. Naphthalene was of ten selected as a model compound for the study of PAH degradation because of its high aqueous solubility and the easy isolation of microbes capable of its degradation. Since the first report of a biochemical pathway for naphthalene oxidation by Pseudomonas species in 1964 by Davis and Evans, extensive studies have rigorously defined the metabolic pathway genes, and enzymes involved. In last decade a number of bacteria that metabolise larger PAHs molecules have been isolated. These include Azoarcus evansii, various Mycobacterium species and several Pseudomonas species. A number of different metabolic pathways have been established for the bacterial degradation of PAHs. The genes coding for the enzymes involved in the degradation of alkanes (alk), naphthalene (nah), benzoate via ortho clavage of catechol (in bacteria) or prothocatechuate (in fungi) by the ß-ketoadipate pathway have been extensively characterized. The various microorganisms species mineralizing four-ring PAHs including phenanthrene, pyrene and chrysene have been also isolated.