The thermodynamic landscape of methanogenic PAH degradation.
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.
Affiliation: School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. Jan.Dolfing@ncl.ac.ukShow MeSH
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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.
Affiliation: School of Civil Engineering and Geosciences, Newcastle University, Newcastle upon Tyne, NE1 7RU, UK. Jan.Dolfing@ncl.ac.uk