Microbial community structure in a thermophilic anaerobic hybrid reactor degrading terephthalate

Abstract

A thermophilic terephthalate-degrading methanogenic consortium was successfully enriched for 272 days in an anaerobic hybrid reactor, and the microbial structure was characterized using terminal RFLPs, clone libraries and fluorescence in-situ hybridization with rRNA-targeted oligonucleotide probes. All the results suggested that Methanothrix thermophila-related methanogens, Desulfotomaculum-related bacterial populations in the Gram-positive low-G+C group, and OP5-related populations were the key members responsible for terephthalate degradation under thermophilic methanogenic conditions except during periods when the reactor experienced heat shock and pump failure. These perturbations caused a significant shift in bacterial population structure in sludge samples taken from the sludge bed but not from the surface of the packing materials. After system recovery, many other bacterial populations emerged, which belonged mainly to the Gram-positive low-G+C group and Cytophaga-Flexibacter-Bacteroides, as well as b-Proteobacteria, Planctomycetes and Nitrospira. These newly emerged populations were probably also capable of degrading terephthalate in the hybrid system, but were out-competed by those bacterial populations before perturbations.

Multiple syntrophic interactions in a terephthalate-degrading methanogenic consortium

“…Using the 16S rRNA gene and McrA gene as biomarkers, temperature-dependent variations were also observed with acetoclastic methanogen populations found in the order Methanosarcinales (Supplementary Figure 4). The hydrogenotrophic methanogens identified here are closely related to methanogens found in mesophilic and thermophilic TA-degrading reactors (Wu et al, 2001;Chen et al, 2004), and together with Methanolinea tarda NOBI-1 recently isolated from anaerobic digestion processes (Imachi et al, 2008), form a novel cluster separate from other known hydrogenotrophic methanogens. The comparison of McrA genes further suggests that the methanogens found in the new cluster are likely different from M. tarda NOBI-1 (Supplementary Figure 4B). )…”

“…Several studies have investigated the microbial populations present in methanogenic TA degradation, often using laboratory-scale reactors operated at various temperatures (Kleerebezem et al, 1999;Wu et al, 2001;Chen et al, 2004). Using ribosomal RNA (rRNA)-based molecular methods, these studies have found that TA-degrading consortia in bioreactors are dominated by two to three bacterial populations and two types of methanogens (Wu et al, 2001;Chen et al, 2004).…”

“…This reactor was constructed with an upper section filled with ring-shape porous filters to support the growth of microbial biofilms, and a lower section for the development of anaerobic granular sludge ( Figure 1a). This reactor is unusual and novel, in that it was the first methanogenic reactor operated in the hyper-mesophilic temperature zone (46-50 1C), whereas previously published studies of TA-degrading communities were at mesophilic (B35 1C) or thermophilic (B55 1C) temperatures (Kleerebezem et al, 1999;Wu et al, 2001;Chen et al, 2004). After achieving a good TA removal efficiency (Figure 1b), sludge samples were taken from the surface of the filter media at days 221, 280, 346 and 430.…”

“…If the syntrophic interaction is disturbed and the treatment rendered ineffective, the resulting high-concentration effluent must be treated with a more energy-intensive down-stream aerobic biological process. These factors can significantly increase the operational cost of the process and limit its application on a wider scale.Several studies have investigated the microbial populations present in methanogenic TA degradation, often using laboratory-scale reactors operated at various temperatures (Kleerebezem et al, 1999;Wu et al, 2001;Chen et al, 2004). Using ribosomal RNA (rRNA)-based molecular methods, these studies have found that TA-degrading consortia in bioreactors are dominated by two to three bacterial populations and two types of methanogens (Wu et al, 2001;Chen et al, 2004).…”

“…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.…”