RN carried out some of the taxonomic analyses. DE performed the FAME analysis. EK constructed the phylogenetic trees and helped in the final version of the manuscript. AS, LSvanO and JDvanE designed the sampling strategy, collaborated in the data analyses and revised the manuscript. All authors read and approved the final LDC000067 order manuscript.”
“Background As the sole producers of biogenic methane, methanogenic Archaea (methanoarchaea) are a unique and poorly

understood group of microorganisms. Methanoarchaea represent some of the most oxygen sensitive organisms identified to date [1], yet many methanogens can withstand oxygen exposure and resume growth once anaerobic conditions have been restored [2–4]. Thus, methanogens must have effective mechanisms for sensing and responding to redox changes in their local environment. Many methanogenic genomes encode homologues of proteins like superoxide dismutase, alkylhydroperoxide reductase, superoxide reducatase, and rubrerythrins that are known to combat oxidative stress

in anaerobes [5–7]. Thus, methanogens potentially have several mechanisms for mitigating the damage caused by temporary oxidative stress. A better understanding of the oxidative stress response in methanogens is important for understanding their contributions to the CBL0137 cell line planetary Cilengitide in vivo ecosystem. At least one methanogenic protein, F420H2 oxidase, has been shown to reduce O2 to H2O [8]. In Methanothermobacter thermautotrophicus, F420H2 oxidase is the product of fpaA (MTH1350) whose promoter, P fpaA , is regulated by the methanogen-specific V4R domain regulator (MsvR). M. thermautotrophicus MsvR (MthMsvR) and its homologues are unique to a subset of methanogens, including the Methanomicrobiales and Methanosarcinales[9]. Besides controlling expression of fpaA, MthMsvR has also been shown to regulate its own expression at the

transcriptional level in vitro. In its reduced state, MthMsvR represses transcription of fpaA and msvR by abrogating the Mannose-binding protein-associated serine protease binding of general transcription factors at the promoter, P fpaA or P msvR , respectively [9]. Except for the use of a bacterial-like regulator, the basal transcriptional machinery of methanogens and all Archaea resembles that of eukaryotes. The multi-subunit RNA polymerase (RNAP) in Archaea resembles the eukaryotic RNAP II complex and is recruited to the promoter by homologues of the eukaryotic TATA binding protein (TBP) and TFIIB (TFB in Archaea). Archaeal transcription regulators can possess either activator or repressor functions and a few rare examples possess both functions [10]. The only clearly defined activation mechanism to date involves recruitment of TBP to the promoter [11], while archaeal repressors bound near the promoter have been shown to repress transcription in several ways, including abrogation of TBP/TFB or RNA polymerase binding to the promoter [10].