Obayori, OS; Ilori, MO; Amund, OO
Pyrene is a peri-condensed four-ring polycyclic aromatic hydrocarbon (PAH). It is highly recalcitrant and a model compound for the study of degradative pathways of other PAHs such as benzo(a)pyrene. Mycobacterium species and some other actinomycetes were the first pyrene metabolizing bacteria to be described starting from 1988. Today, pyrene is known to be metabolized by a broad range of bacteria including Gram-negatives such as Pseudomonas, Sphingomonas, Stenotromorpha, Alcaligenes, Achromobacter, Leclercia, Cycloclasticus and Burkholderia among others. The main pathway of pyrene metabolism is via dioxygenation at the 4,5-position followed by ortho cleavage to produce 4,5-dihydroxy-4,5-dihydro phenanthrene and subsequent sequential cleavage leading to the tricarboxylic acid (TCA) cycle via O-phthalate. Another pathway, less common, proceeds through the cleavage of the two central rings at the 4, 5-and 9, 10-positions to produce a unique metabolite 6,6'-dihydroxy-2,2'-biphenyl dicarboxylic acid which also proceeds through O-phthalate but in fewer steps. Dioxygenation at the 1,2 position often leads to methylated dead-end products or detoxification. There are also reports of cometabolism of pyrene in the presence of co-substrates such as phenanthrene and fluoranthene. Bacterial metabolism of pyrene is modulated by factors such as pH, temperature, salinity, biosurfactants and humic acids amongst others. Products of incomplete metabolism of pyrene have been shown to inhibit degradation of other PAHs in the environment. In Mycobacterium species, especially, genes for pyrene metabolism are localized both on chromosomes and on plasmids. However, not much is known yet about the metabolism and genomics of Gram-negative pyrene degraders. Therefore, efforts are expected to be directed in this direction in the near future. © 2013 by Nova Science Publishers, Inc. All rights reserved.