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The thermodynamic landscape of methanogenic PAH degradation.

Dolfing J, Xu A, Gray ND, Larter SR, Head IM - Microb Biotechnol (2009)

Bottom Line: Depending on the in situ conditions the energetically most favourable pathway for the PAH-degrading organisms is oxidation to H(2)/CO(2) or conversion into acetate.These are not necessarily the pathways that prevail in the environment.This may be because the kinetic theory of optimal length of metabolic pathways suggests that PAH degraders may have evolved towards incomplete oxidation to acetate plus H(2) as the optimal pathway.

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Affiliation: School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. Jan.Dolfing@ncl.ac.uk

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Hydrogen and acetate as thermodynamic constraints on methanogenic phenanthrene degradation. The windows of opportunity for the various pathways are indicated in grey. (i) complete oxidation of PAHs to H2 and CO2, linked to methanogenesis from CO2 reduction; (ii) oxidation of PAHs to acetate and H2, linked to acetoclastic methanogenesis and CO2 reduction; (iia) oxidation of PAHs to acetate and H2, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction; (iii) oxidation of PAHs to acetate alone, linked to acetoclastic methanogenesis; (iiia) oxidation of PAHs to acetate alone, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction. For a definition of the domains I to VI see Fig. 3.
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f4: Hydrogen and acetate as thermodynamic constraints on methanogenic phenanthrene degradation. The windows of opportunity for the various pathways are indicated in grey. (i) complete oxidation of PAHs to H2 and CO2, linked to methanogenesis from CO2 reduction; (ii) oxidation of PAHs to acetate and H2, linked to acetoclastic methanogenesis and CO2 reduction; (iia) oxidation of PAHs to acetate and H2, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction; (iii) oxidation of PAHs to acetate alone, linked to acetoclastic methanogenesis; (iiia) oxidation of PAHs to acetate alone, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction. For a definition of the domains I to VI see Fig. 3.

Mentions: The windows of opportunity with respect to acetate and H2 have been summarized for the range of processes that are presumably involved in methanogenic PAH degradation (Figs 3–5). Figure 3 elaborates the case for methanogenic naphthalene degradation. This analysis allows identification of clear zones where different methanogenic phenanthrene degradation pathways can occur. For example, the window of opportunity linking conversion of naphthalene to acetate with acetoclastic methanogenesis (domain I to IV and VI in Fig. 3) is much larger than the equivalent window for linking incomplete oxidation of naphthalene to both acetoclastic methanogenesis and methanogenic CO2 reduction (domain II, III and IV and VI in Fig. 3), or complete oxidation of naphthalene linked to methanogenic CO2 reduction (domain II, IV and V in Fig. 3). This is summarized in Fig. 4. A comparison of Fig. 3 and Fig. 5 shows that this observation holds for all five PAHs evaluated here.


The thermodynamic landscape of methanogenic PAH degradation.

Dolfing J, Xu A, Gray ND, Larter SR, Head IM - Microb Biotechnol (2009)

Hydrogen and acetate as thermodynamic constraints on methanogenic phenanthrene degradation. The windows of opportunity for the various pathways are indicated in grey. (i) complete oxidation of PAHs to H2 and CO2, linked to methanogenesis from CO2 reduction; (ii) oxidation of PAHs to acetate and H2, linked to acetoclastic methanogenesis and CO2 reduction; (iia) oxidation of PAHs to acetate and H2, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction; (iii) oxidation of PAHs to acetate alone, linked to acetoclastic methanogenesis; (iiia) oxidation of PAHs to acetate alone, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction. For a definition of the domains I to VI see Fig. 3.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC3815364&req=5

f4: Hydrogen and acetate as thermodynamic constraints on methanogenic phenanthrene degradation. The windows of opportunity for the various pathways are indicated in grey. (i) complete oxidation of PAHs to H2 and CO2, linked to methanogenesis from CO2 reduction; (ii) oxidation of PAHs to acetate and H2, linked to acetoclastic methanogenesis and CO2 reduction; (iia) oxidation of PAHs to acetate and H2, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction; (iii) oxidation of PAHs to acetate alone, linked to acetoclastic methanogenesis; (iiia) oxidation of PAHs to acetate alone, linked to syntrophic acetate oxidation and methanogenesis from CO2 reduction. For a definition of the domains I to VI see Fig. 3.
Mentions: The windows of opportunity with respect to acetate and H2 have been summarized for the range of processes that are presumably involved in methanogenic PAH degradation (Figs 3–5). Figure 3 elaborates the case for methanogenic naphthalene degradation. This analysis allows identification of clear zones where different methanogenic phenanthrene degradation pathways can occur. For example, the window of opportunity linking conversion of naphthalene to acetate with acetoclastic methanogenesis (domain I to IV and VI in Fig. 3) is much larger than the equivalent window for linking incomplete oxidation of naphthalene to both acetoclastic methanogenesis and methanogenic CO2 reduction (domain II, III and IV and VI in Fig. 3), or complete oxidation of naphthalene linked to methanogenic CO2 reduction (domain II, IV and V in Fig. 3). This is summarized in Fig. 4. A comparison of Fig. 3 and Fig. 5 shows that this observation holds for all five PAHs evaluated here.

Bottom Line: Depending on the in situ conditions the energetically most favourable pathway for the PAH-degrading organisms is oxidation to H(2)/CO(2) or conversion into acetate.These are not necessarily the pathways that prevail in the environment.This may be because the kinetic theory of optimal length of metabolic pathways suggests that PAH degraders may have evolved towards incomplete oxidation to acetate plus H(2) as the optimal pathway.

View Article: PubMed Central - PubMed

Affiliation: School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. Jan.Dolfing@ncl.ac.uk

Show MeSH
Related in: MedlinePlus