Effects of Polycyclic Aromatic Hydrocarbon Mixtures on Degradation, Gene Expression, and Metabolite Production in Four Mycobacterium Species

Abstract

Polycyclic aromatic hydrocarbons (PAHs) are widespread environmental contaminants that are hazardous to human health. It has been demonstrated that members of the Mycobacterium genus are among the most effective degraders of PAHs, but few studies have focused on the degradation of PAH mixtures. In this study, single and mixed PAH metabolism was investigated in four phylogenetically distinct Mycobacterium species with respect to (i) parent compound degradation, (ii) bacterial growth, (iii) catabolic gene expression, and (iv) metabolite production. Synergistic and antagonistic effects on four model PAH compounds (benzo[a]pyrene, pyrene, fluoranthene, and phenanthrene) characterized degradation of mixtures in a strain-and mixture-dependent manner. The mixture of pyrene and phenanthrene, in particular, resulted in antagonized degradation by three out of four bacterial species, and further studies were narrowed to investigate the degradation of this mixture. Antagonistic effects persisted over time and were correlated with reduced bacterial growth. Antagonized degradation of PAH was not caused by preferential degradation of secondary PAHs, nor were mixture compounds or concentrations toxic to cells growing on sugars. Reverse transcription-PCR (RT-PCR) studies of the characterized catabolic pathway of phenanthrene showed that in one organism, antagonism of mixture degradation was associated with downregulated gene expression. Metabolite profiling revealed that antagonism in mixture degradation was associated with the shunting of substrate through alternative pathways not used during the degradation of single PAHs. The results of this study demonstrate metabolic differences between single and mixed PAH degradation with consequences for risk assessment and bioremediation of PAH-contaminated sites. IMPORTANCEMycobacterium species are promising organisms for environmental bioremediation because of their ubiquitous presence in soils and their ability to catabolize aromatic compounds. PAHs can be degraded effectively as single compounds, but mixed substrates often are subject to degradative inhibition, which may explain the persistence of these pollutants in soils. Single and mixed PAH degradation by diverse Mycobacterium species was compared, with associated bacterial growth, gene expression, and metabolite production. The results demonstrate that antagonism characterized degradation in a strain-and mixture-dependent manner. One strain that was versatile in its pathway use of single chemicals also efficiently degraded the mixture, whereas antagonism in other the strains was associated with altered metabolic profiles, indicating unusual pathway use. The impacts of this work on risk assessment and bioremediation modeling studies indicate the need to account for mixture-generated intermediates and to recognize mixture degradation as a property distinct from that of PAH substrate range. P olycyclic aromatic hydrocarbons (PAHs) are a class of chemical pollutants that are widespread and persistent in the environment (1-3...

Phenanthrene contamination and ploidy level influence the rhizosphere microbiome of Spartina

“…Interestingly, Cycloclasticus spp. were often reported as one of the predominant PAH degraders in seawater (37, 38), whereas Mycobacterium are typical soil PAH degraders (39) and Massilia were found to degrade PAHs in soils or associated to roots (40, 41). This diversity of putative PAH degraders associated with the rhizosphere of Spartina is probably linked to the nature of its habitat, at the interface of terrestrial, plant and maritime ecosystems.…”

Formation of Developmentally Toxic Phenanthrene Metabolite Mixtures by Mycobacterium sp. ELW1

“…strain 6PY1, M. vanbaalenii strain PYR-1, and Sphingomonas sp. strain A4, 55–58 cis -9,10-OHPHE by M. aromativorans JS19b1, 57–60 and cis -1,2-dihydroxy-1,2-dihydrophenanthrene ( cis -1,2-OHPHE) by M. aromativorans JS19b1, 57,59 have been measured in other studies. Kim et al also measured additional OHPHE metabolites including 2-and 3-OHPHE, 9,10-OHPHE, and one additional phenanthrenediol.…”

“…strains, including and PYRGCK, JS19b1, czh-3, and czh-117 (−0.0020 to −0.019 µmol hr −1 ) and A1-PYR (−0.019 µmol hr −1 ). 60,62 …”

NarL, a Novel Repressor for CYP108j1 Expression during PAHs Degradation in Rhodococcus sp. P14

“…These PAHs can bioaccumulate through food chains, which poses a potential hazard to human health [4][5][6][7]. Bioremediation is considered a useful and available cleanup strategy and much scientific work has focused on analysis of the bacterial catabolism of PAHs [8][9][10]. In the last few decades, research on microbial degradation of PAHs has advanced significantly and a number of PAH-degrading isolates have been reported [1,[11][12][13], with some of the isolates belonging to the Rhodococcus genus.…”