Anaerobic Degradation of Phthalate Isomers by Methanogenic Consortia

Abstract

Three methanogenic enrichment cultures, grown onortho-phthalate, iso-phthalate, or terephthalate were obtained from digested sewage sludge or methanogenic granular sludge. Cultures grown on one of the phthalate isomers were not capable of degrading the other phthalate isomers. All three cultures had the ability to degrade benzoate. Maximum specific growth rates (μS max) and biomass yields (YXtot S) of the mixed cultures were determined by using both the phthalate isomers and benzoate as substrates. Comparable values for these parameters were found for all three cultures. Values for μS max and YXtot S were higher for growth on benzoate compared to the phthalate isomers. Based on measured and estimated values for the microbial yield of the methanogens in the mixed culture, specific yields for the phthalate and benzoate fermenting organisms were calculated. A kinetic model, involving three microbial species, was developed to predict intermediate acetate and hydrogen accumulation and the final production of methane. Values for the ratio of the concentrations of methanogenic organisms, versus the phthalate isomer and benzoate fermenting organisms, and apparent half-saturation constants (KS) for the methanogens were calculated. By using this combination of measured and estimated parameter values, a reasonable description of intermediate accumulation and methane formation was obtained, with the initial concentration of phthalate fermenting organisms being the only variable. The energetic efficiency for growth of the fermenting organisms on the phthalate isomers was calculated to be significantly smaller than for growth on benzoate.

Enzymes involved in the anaerobic degradation of ortho‐phthalate by the nitrate‐reducing bacterium Azoarcus sp. strain PA01

“…Aftring et al, showed that phthalate isomers can be degraded under anoxic conditions (Aftring et al, 1981). Although less understood than aerobic phthalate degradation, anaerobic degradation of phthalate isomers and phthalate esters was reported for numerous pure and mixed cultures under nitrate-or sulfate-reducing or methanogenic conditions (Battersby and Wilson, 1989;Kleerebezem et al, 1999;Qiu et al, 2006;Cheung et al, 2007;Liang et al, 2008), but no decisive studies on the degradation pathways have been published so far.…”

Energetics of product formation during anaerobic degradation of phthalate isomers and benzoate

“…Medium, substrate and BES were added to the bottles from concentrated stock solutions. The composition of the medium has been described elsewhere [19]. Either the phthalate isomer or a mixture of the phthalate isomer and benzoate was used as substrate at concentrations between 2 and 5 mM.…”

“…Three enrichment cultures were used with the ability to degrade either phthalate, isophthalate or terephthalate. The cultures were obtained from digested sewage sludge or granular sludge and were enriched on one of the three phthalate isomers as described previously [19]. The phthalate isomer-grown cultures had the ability to degrade benzoate without a lag phase, at rates comparable to the phthalate isomers' degradation rates.…”

“…Considering, however, that anaerobic fermentations have been observed at Gibbs free energy changes much closer to 0 kJ mol 31 , it may be suggested that electron transport across the cytoplasmic membrane and ATP formation should be variable, implying that any exergonic reaction may sustain growth [18]. In previous studies we described the kinetics and related speci¢c characteristics of three methanogenic enrichment cultures grown on phthalate, isophthalate and terephthalate [19,20]. It was postulated in these papers that the phthalate isomers are fermented to a mixture of acetate and hydrogen with benzoate (or benzoyl-CoA) as the central intermediate, analogous to the denitrifying organism Pseudomonas K136 [21,22].…”

Co‐occurrence network analysis reveals thermodynamics‐driven microbial interactions in methanogenic bioreactors

“…Given that one ton of PTA production incurs 2.5-10 m 3 of wastewater that is subsequently treated before discharge into receiving water bodies, PTA production generates approximately 120-478 × 10 6 m 3 year −1 of wastewater (Kleerebezem et al, 2005;Razo-Flores et al, 2006). This wastewater contains varying concentrations of aromatic compounds (Roffia et al, 1984;Kleerebezem et al, 1999;Razo-Flores et al, 2006;Tomás et al, 2013); thus, necessitating effective treatment. Anaerobic biological processes treating PTA process wastewater (Guyot et al, 1990;Macarie, 2000;Stergar et al, 2003;Van Lier et al, 2008;Kim et al, 2012;Narihiro et al, 2015a) promote a microbial reaction where syntrophic substrate-oxidizing bacteria (syntrophs) forge a mutually supportive partnership with methanogenic archaea (methanogens) to accomplish oxidation of aromatic compounds (Qiu et al, 2006;McInerney et al, 2007;Qiu et al, 2008;Schink and Stams, 2013;Nobu et al, 2014;Aida et al, 2015;Nobu et al, 2015a, b).…”