Microbial metabolism of polycyclic aromatic hydrocarbons: isolation and characterization of a pyrene-degrading bacterium

Abstract

Microbiological analyses of sediments located near a point source for petrogenic chemicals resulted in the isolation of a pyrene-mineralizing bacterium. This isolate was identified as a Mycobacterium sp. on the basis of its cellular and colony morphology, gram-positive and strong acid-fast reactions, diagnostic biochemical tests, 66.6% G+C content of the DNA, and high-molecular-weight mycolic acids (C58 to C64). The mycobacterium mineralized pyrene when grown in a mineral salts medium supplemented with nutrients but was unable to utilize pyrene as a sole source of carbon and energy. The mycobacterium grew well at 24 and 30°C and minimally at 35°C. No growth was observed at 5 or 42°C. The mycobacterium grew well at salt concentrations up to 4%. Pyrene-induced Mycobacterium cultures mineralized 5% of the pyrene after 6 h and reached a maximum of 48% mineralization within 72 h. Treatment of induced and noninduced cultures with chloramphenicol showed that pyrene-degrading enzymes were inducible in this Mycobacterium sp. This bacterium could also mineralize other polycyclic aromatic hydrocarbons and alkyl-and nitro-substituted polycyclic aromatic hydrocarbons including naphthalene, phenanthrene, fluoranthene, 3-methylcholanthrene, 1-nitropyrene, and 6-nitrochrysene. This is the first report of a bacterium able to extensively mineralize pyrene and other polycyclic aromatic hydrocarbons containing four aromatic rings.

THE EFFECT OF POLYCYCLIC AROMATIC HYDROCARBONS ON THE DEGRADATION OF BENZO[a]PYRENE BY MYCOBACTERIUM SP. STRAIN RJGII-135

“…Pyrene has also been shown to induce PAH degradation in Mycobacterium sp. strain PYR-1 [7]. In addition, cross induction of phenanthrene and pyrene degradation by each respective substrate has been reported for a Mycobacterium sp.…”

“…However, mineralization may be underestimated because of the position of the radiolabel [9-14 C]-anthracene. Preferential utilization of pyrene and phenanthrene over PAHs that are cometabolized is a common finding in PAH-degrading mycobacteria [4,7,9,11,12,19]. Given the growing number of unique mycobacteria stains found to have pyrene-and phenanthrenedegradative activity, it is possible that metabolism of these compounds is an inherent property for at least some members of this genera.…”

“…The 7,8-BaP dihydrodiol metabolite did not accumulate over a 72-h time course, possibly reflecting that the initial metabolic conversion of BaP is the rate-limiting step. Initial oxidation of PAH compounds has been hypothesized to be a rate-limiting step and may be a target for enhancement of bioremediation to remove recalcitrant PAHs [7,31].…”

“…Although numerous microorganisms have been isolated that degrade PAHs that contain three aromatic rings or less, only a few have been found that can break down structures with four or more rings [3][4][5][6]. Isolation of these organisms through enrichment isolation methods for four-and five-ring degrading bacteria has often resulted in isolation of mycobacteria [4,[7][8][9][10][11][12]. Sequence analysis of the 16S ribosomal DNA indicates that each isolate is a distinct species of Mycobacterium [10][11][12][13][14].…”

“…Evidence exists that Mycobacterium spp. can act on more than one compound, and in some cases a single isolate can degrade both low-and high-molecular-weight compounds [4,7,9,11]. It is poorly understood how enzymatic activity against high-molecular-weight PAHs is maintained in the presence of other PAHs, particularly in organisms that can degrade a wide range of substrates.…”