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#hydrocarbon degradation

2 public questions tagged with this topic.

Bioremediation

White rot fungi degrade hydrocarbons using:

White rot fungi including Phanerochaete chrysosporium, Trametes versicolor and Pleurotus ostreatus possess unique extracellular oxidative lignin-degrading machinery evolved to depolymerize wood lignin polymer composed of phenylpropanoid units linked via ether and carbon-carbon bonds, which serendipitously attacks structurally similar persistent organic pollutants including benzo[a]pyrene, polychlorinated biphenyls, dioxins and pentachlorophenol. Key enzymes secreted under nutrient nitrogen limitation triggering secondary metabolism are lignin peroxidase LiP isoenzymes oxidizing veratryl alcohol to radical cation with redox potential 1.4 volts capable of abstracting electrons from non-phenolic aromatics, manganese peroxidase MnP oxidizing Mn2+ to Mn3+ chelated by oxalate that diffuses as small reactive oxidizer attacking phenolic structures, and versatile peroxidase VP combining both activities plus laccase using oxygen and mediator ABTS. Generation of highly reactive free radicals leads to non-specific, non-stereoselective oxidative cleavage of C-C and C-O bonds producing quinones that undergo subsequent ring opening. Reactions require hydrogen peroxide continuously supplied by glyoxal oxidase and aryl alcohol oxidase. Because oxidation is extracellular and radical-mediated rather than requiring substrate uptake, white rot fungi degrade high molecular weight PAHs unavailable to bacterial intracellular dioxygenases, explaining superiority for complex hydrocarbon mixtures.

Ref: Pointing White rot fungi role in bioremediation Applied Microbiology Biotechnology 2001; Wesenberg et al. lignin peroxidase mechanism; PubMed PAH fungal.

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Bioremediation

Which microorganism is known to degrade aromatic hydrocarbons?

Pseudomonas putida strains such as KT2440 certified HV1 safety, mt-2 and F1 embody archetypal aerobic degraders of monoaromatic and polycyclic aromatic hydrocarbons due to extraordinary metabolic versatility conferred by large genome 6.2 megabases encoding more than 80 oxygenases and multiple catabolic plasmids including TOL plasmid pWW0 carrying upper pathway xylCMABN converting toluene and xylene to benzoate via xylene monooxygenase multicomponent system and meta-cleavage lower pathway xylXYZLTEGFJKIH, and NAH7 plasmid encoding naphthalene dioxygenase nahAc. Enzymatic repertoire includes toluene dioxygenase todC1C2BA introducing dioxygen to form cis-dihydrodiols, catechol 2,3-dioxygenase xylE catalyzing extradiol ring fission producing yellow 2-hydroxymuconic semialdehyde, and central tricarboxylic acid cycle integration. Chemotaxis genes che regulate flagellar movement toward aromatic gradients increasing bioavailability. Strain thrives in contaminated soils at densities 10^6 per gram, grows on benzene, toluene, ethylbenzene and xylene as sole carbon sources with generation time 2 to 3 hours. Unlike Escherichia coli lacking oxygenase repertoire, Lactobacillus focusing on sugar fermentation, Streptococcus pathogenic without catabolic plasmids, P. putida evolved in polluted niches possessing regulatory networks XylR and TodST responding to aromatic inducers, enabling rapid mineralization to CO2 with high specific affinity.

Ref: Timmis Pseudomonas putida review Nature Reviews Microbiology 2002; EPA aromatic degraders guide; PubMed KT2440 genome PMID 12055322.

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