Multiple syntrophic interactions in a terephthalate-degrading methanogenic consortium

Abstract

Terephthalate (TA) is one of the top 50 chemicals produced worldwide. Its production results in a TA-containing wastewater that is treated by anaerobic processes through a poorly understood methanogenic syntrophy. Using metagenomics, we characterized the methanogenic consortium inside a hyper-mesophilic (that is, between mesophilic and thermophilic), TA-degrading bioreactor. We identified genes belonging to dominant Pelotomaculum species presumably involved in TA degradation through decarboxylation, dearomatization, and modified b-oxidation to H 2 /CO 2 and acetate. These intermediates are converted to CH 4 /CO 2 by three novel hyper-mesophilic methanogens. Additional secondary syntrophic interactions were predicted in Thermotogae, Syntrophus and candidate phyla OP5 and WWE1 populations. The OP5 encodes genes capable of anaerobic autotrophic butyrate production and Thermotogae, Syntrophus and WWE1 have the genetic potential to oxidize butyrate to CO 2 /H 2 and acetate. These observations suggest that the TA-degrading consortium consists of additional syntrophic interactions beyond the standard H 2 -producing syntroph-methanogen partnership that may serve to improve community stability. The ISME Journal (2011) 5, 122-130; doi:10.1038/ismej.2010; published online 5 August 2010Subject Category: integrated genomics and post-genomics approaches in microbial ecology Keywords: metagenomics; methanogenesis; syntroph; microbial diversity; carbon cycling Introduction Terephthalate (TA) is used as the raw material for the manufacture of numerous plastic products (for example, polyethylene TA bottles and textile fibers). During its production, TA-containing wastewater is discharged in large volumes (as high as 300 million m 3 per year) and high concentration (up to 20 kg COD (chemical oxygen demand) m À3 ) (Razo-Flores et al., 2006). This wastewater is generally treated by anaerobic biological processes under mesophilic conditions (B35 1C). However, anaerobic processes operated at hyper-mesophilic (46-50 1C) and thermophilic (B55 1C) temperatures may be preferable because of the ability to achieve higher loading rate (van Lier et al., 1997;Chen et al., 2004), which reduces the reactor volume. Moreover, TA wastewater is usually generated at 54-60 1C, and does not require additional energy input for maintaining reactor temperature (Chen et al., 2004). The microbial biomass usually occurs in the form of granules or biofilms attaching on the surface of porous media. Under such environments, TA degradation has been hypothesized (Kleerebezem et al., 1999) to be based on a syntrophic microbial relationship whereby fermentative H 2 -producing bacteria (syntrophs) convert TA through benzoate to acetate and H 2 /CO 2 , and acetoclastic and hydrogenotrophic methanogens further convert the intermediates to methane by physically positioning themselves close to the syntrophs to overcome the www.nature.com/ismej thermodynamic barrier (Stams, 1994;Conrad, 1999;Dolfing, 2001).In practice, the complexities of TA-degrading communities are not...

Microbial dark matter ecogenomics reveals complex synergistic networks in a methanogenic bioreactor

“…Our recent metagenomic and proteomic studies proposed that Pelotomaculum may produce acetate, H 2 and butyrate as by-products and that uncultivated taxa (Caldiserica and 'Ca. Cloacimonetes', formerly OP5 and WWE1) may further metabolize H 2 and butyrate (Lykidis et al, 2011;Wu et al, 2013). This provided evidence that non-methanogen community members may serve as syntrophic partners (secondary degraders) to metabolize TA degradation by-products alongside aceticlastic and hydrogenotrophic methanogens.…”

“…The 1.2-l hybrid reactor was packed with tubular ceramic carrier (Siporax, sera GmbH, Immenhausen, Germany) and fed TA as the sole energy source (3.6 g l À 1 TA per day) in an anaerobic mineral culture medium (Chen et al, 2004;Lykidis et al, 2011). For single-cell collection, biofilms were separated from the carrier, dispersed through sonication and sorted through flow cytometry.…”

“…Syntrophs specifically form obligate mutualistic interactions with methanogens to metabolize organic compounds whose degradation otherwise rapidly becomes thermodynamically unfavorable (DG40) as by-products accumulate (Schink, 1997;Schink and Stams, 2006). Despite such low-energy conditions, engineered and natural methanogenic environments harbor a wide diversity of uncharacterized microorganisms from known phyla and candidate phyla without cultivated representatives (microbial dark matter; Rinke et al, 2013; also see Juottonen et al, 2005;Nemergut et al, 2008;Griebler and Lueders, 2009;Riviere et al, 2009;Glockner et al, 2010;Kong et al, 2010;Kim et al, 2011;Lykidis et al, 2011;Nelson et al, 2011;Rinke et al, 2013). Their presence indicates many undiscovered microbial niches and interactions.…”

“…An excellent example of a methanogenic community rich in uncultivated taxa is a hypermesophilic bioreactor (46-50 1C) treating terephthalate (TA), a major waste product of plastic manufacturing (Lykidis et al, 2011). Pelotomaculum and Syntrophorhabdus are known to syntrophically metabolize TA (Wu et al, 2001;Qiu et al, 2004Qiu et al, , 2006Qiu et al, , 2008.…”

Comparative analysis of metagenomes from three methanogenic hydrocarbon-degrading enrichment cultures with 41 environmental samples

“…Methanogenic biodegradation of hydrocarbons is important in many environments such as contaminated groundwater, sediments and organic chemical waste disposal sites that are devoid of electron acceptors such as oxygen, nitrate, iron(III) and sulfate (Chang et al, 2005, Essaid et al, 2011Lykidis et al, 2011). Methanogenic hydrocarbon biodegradation is also an important biogeochemical process in subsurface fossil energy reservoirs that, over geological time, has contributed to the formation of natural gas deposits and/or the conversion of light oil to heavy oil (Jones et al, 2008).…”