c Degradation of terephthalate (TA) through microbial syntrophy under moderately thermophilic (46 to 50°C) methanogenic conditions was characterized by using a metagenomic approach (A. Lykidis et al., ISME J. 5:122-130, 2011). To further study the activities of key microorganisms responsible for the TA degradation, community analysis and shotgun proteomics were used. The results of hierarchical oligonucleotide primer extension analysis of PCR-amplified 16S rRNA genes indicated that Pelotomaculum, Methanosaeta, and Methanolinea were predominant in the TA-degrading biofilms. Metaproteomic analysis identified a total of 482 proteins and revealed a distinctive distribution pattern of microbial functions expressed in situ. The results confirmed that TA was degraded by Pelotomaculum spp. via the proposed decarboxylation and benzoyl-coenzyme A-dependent pathway. The intermediate by-products, including acetate, H 2 /CO 2 , and butyrate, were produced to support the growth of methanogens, as well as other microbial populations that could further degrade butyrate. Proteins related to energy production and conservation, and signal transduction mechanisms (that is, chemotaxis, PAS/GGDEF regulators, and stress proteins) were highly expressed, and these mechanisms were important for growth in energy-limited syntrophic ecosystems.T erephthalate (TA) is produced in large quantities in plastic, textile, and petroleum-related industries, and wastewater generated by the TA manufacturing process is often treated with anaerobic methanogenic processes (1). In these processes, TA is converted to CH 4 and CO 2 through the microbial syntrophy established among the enriched microbial populations. It is hypothesized that the hydrogen-producing syntrophic bacteria degrade TA to acetate and H 2 /CO 2 , which are immediately used by the methanogenic archaea adjacent to final gaseous products (2, 3). To validate the syntrophic interaction, a full-cycle 16S rRNA approach was used to successfully identify the identities of the syntrophic bacteria and methanogenic archaea inside the granules and biofilms of different laboratory-scale TA-degrading methanogenic reactors (3, 4). A recent study further used a metagenomic approach to reveal the diversity and physiological traits of the syntrophs and methanogens involved in the TA degradation under moderately thermophilic conditions (46 to 50°C) (5). All of these studies have provided strong evidence to elucidate the degradation of TA based on the microbial populations and the metabolic pathways involved.Furthermore, to directly observe the global expression of microbial functions within the TA-degrading consortium, community-level proteomics can be used (6). To do so, total proteins recovered from an environmental sample are first separated and enzymatically fragmented. The resulting peptide mixture is analyzed using advanced liquid chromatography-mass spectrometry (LC-MS) technology, and information related to the key proteins is identified using in silico analysis of the protein sequence database. ...