Recent Advances in the Biodegradation of Polycyclic Aromatic Hydrocarbons by Mycobacterium Species

Abstract

Polycyclic aromatic hydrocarbons (PAHs) constitute a class of organic compounds containing two or more fused benzene rings in linear, angular, and cluster arrangements. The environmental fate of these ubiquitous contaminants is of concern because of the mutagenicity, ecotoxicity, and carcinogenic potential of high-molar-mass PAHs. A variety of bacterial species have been isolated that have the ability to degrade PAHs with two rings (naphthalene) and three rings (anthracene and phenanthrene). Most of the research on the degradative biochemical pathways, the genes involved in PAH metabolism, and genetic regulation has been on Pseudomonas, Sphingomonas, Burkholderia, and Comamonas strains. Recent reports have shown that various Mycobacterium, Nocardia, and Rhodococcus species have the ability to degrade PAHs containing more than three rings (such as pyrene, fluoranthene, and benzo[a]pyrene). Mycobacterium sp. PYR-1 (reclassified as Mycobacterium vanbaalenii strain PYR-1), which was originally isolated from oil-contaminated estuarine and marine sediments, is capable of mineralizing PAHs, such as naphthalene, pyrene, fluoranthene, phenanthrene, anthracene and benzo[a]pyrene. Biodegradation pathways have been elucidated which suggest that Mycobacterium sp. PYR-1 metabolizes PAHs through similar and unique catabolic pathways compared to that reported for Gram-negative bacteria. Mycobacterium sp. PYR-1 enhanced the degradation of four different aromatic ring classes of PAHs when inoculated into microcosms containing sediment and water from estuarine and freshwater environments. Molecular techniques to detect the Mycobacterium indicated that it survived and performed well in mixed-sediment microbial populations. Analysis of protein expression in Mycobacterium sp. PYR-1 using 2-dimensional Polyacrylamide gel electrophoresis enabled detection of several major proteins whose activity was increased after induction by PAHs. The cloning and sequence analysis of some of the genes encoding PAH degradation have been conducted. These studies demonstrate the bioremediation potential of Mycobacterium species to degrade PAHs in aquatic and terrestrial environments.