Three fosmid clones harboring bathyarchaeotal genomic fragments were screened from the South China Sea sediments (05 cm depth) (Lietal.2012). Our results provide an overview of the archaeal population, The Subgroups-1, -6 and -15 genomes also encoded the methyl glyoxylate pathway, which is typically activated when slow-growing cells are exposed to an increased supply of sugar phosphates (Weber, Kayser and Rinas 2005). Bathyarchaeotal subgroups analyzed here acquired an almost complete EmbdenMeyerhof Parnas glycolysis pathway. Later on, members of Bathyarchaeota were also found to be abundant in deep marine subsurface sediments (Reedetal.2002; Inagakietal.2003), suggesting that this group of archaea is not restricted to terrestrial environments, and the name has been changed to MCG archaea (Inagakietal.2003). Methanogenic archaea in peatlands WebHost. For instance, a study into the stratification of the archaeal community from a shallow sediment in the Pearl River Estuary defined bathyarchaeotal subgroups from MCG-A to -F (Jiangetal.2011), including the NT-A3 group, which is predominantly isolated from the hydrate stability zone in the deep subsurface hydrate-bearing marine sediment core in the Nankai Trough (Reedetal.2002); meanwhile, an investigation of archaeal composition in ca 200 m deep sub-seafloor sediment cores at the offshore Peru Margin ODP sites 1228 and 1229 listed Bathyarchaeota subgroups PM-1 to -8 (Websteretal.2006). Logares R, Brate J, Bertilsson S et al. Bathyarchaeia occurrence in rich methane sediments Furthermore, the phylogeny of concatenated alignments constituting 12 ribosomal proteins obtained from currently available bathyarchaeotal genomes (from GenBank, 29 November 2017 updated) was also reconstructed, which showed a similar topology to those of 16S rRNA genes with a few exceptions in Subgroup-17 (Fig. Acetyl-CoA might be involved in acetate generation in a fermentative pathway; however, genomic evidence suggests that Subgroup-1 cells might rely on both fermentative and respiratory metabolism (a simple respiratory metabolism based on a membrane-bound hydrogenase). All sequences were clustered at 90% identity using Usearch v10.0.240 (https://www.drive5.com/usearch/), then the 16S rRNA gene sequences from available bathyarchaeotal genomes in public database, the anchor sequences from Kuboetal. Similar community structures across different bathyarchaeotal subgroups were revealed using the two primer pairs; however, both pairs performed poorly with respect to indicating the prevalence of Subgroup-15 in cDNA libraries from freshwater sediments (Filloletal.2015). The members of Bathyarchaeota were positively and strongly correlated especially with the acetoclastic Methanosaeta; however, the second most abundant archaeal group, MG-I (subordinate to Thaumarchaeota) is negatively correlated with other groups, probably indicating segregation corresponding to two distinct lifestyles in this case (Liuetal.2014). It has been suggested that Bathyarchaeota is one of the cosmopolitan groups frequently detected in the freshwater and marine sediments (68% of all sediments analyzed), accounting for a large proportion of the sediment microbial communities (average 36 22%) (Filloletal.2016). Bathyarchaeota was the most abundant archaeal phylum in most samples, accounting for 13.8164.14% of archaeal sequences (Fig. Although the Pta-Ack pathway has been previously identified in the methanogenic genus Methanosarcina, it was shown that the encoding pta-ack gene pair might be derived from a horizontal transfer of genes of bacterial origin (Fournier and Gogarten 2008). The emergence of freshwater-adapted lineages, including freshwater-indicative Subgroups-5, -7, -9 and -11, occurred after the first salinefreshwater transition event (Filloletal.2016). Archaea They also acquired some subunits of coenzyme F420 hydrogenase; this enzyme generates reduced ferredoxin, with hydrogen as the electron donor, as an alternative to MvhADG in many Methanomicrobiales (Thaueretal.2008; Lazaretal.2016; Sousaetal.2016). The phylogenetic affiliation of sequences found in peat suggest that members of the thus-far-uncultivated group Candidatus Bathyarchaeota (representing a fourth phylum) may be involved in methane cycling, either anaerobic oxidation of methane and/or methanogenesis, as at least a few organisms within this group contain the essential Second, determining whether the methane cycling capacity is confined to certain subgroups or whether numerous subgroups or lineages are capable of methane cycling, and if so, the nature of their shared evolutionary or genomic characteristics, is of utmost importance. However, according to the genomic information on most archaeal acetogens and bathyarchaeotal genomic bins obtained by Lazaretal. Diverse Bathyarchaeotal Lineages Dominate Archaeal Hlne A, Mylne H, Christine D et al. The in silico tests revealed that primers MCG528, MCG493, MCG528 and MCG732 cover 87, 79, 44 and 27% of sequences of Subgroups-1 to -12 on average, respectively. Furthermore, genes encoding ATP sulfurylase, for the reduction of sulfate to adenosine 5-phosphosulfate, and adenylyl-sulfate reductase, for the reduction of adenosine 5-phosphosulfate to sulfite, were identified in a metagenomic assembly of Bathyarchaeota TCS49 genome from the Thuwal cold seep brine pool of the Red Sea; this suggests that specific bathyarchaeotal members might harbor a dissimilatory sulfate reduction pathway, indicating the existence of additional potential metabolic capacities of Bathyarchaeota (Zhangetal.2016). These archaeal groups are the phylogenetically closest ones to the protoeukaryote that served as the mitochondrion-acquiring host; this gave rise to a hydrogen hypothesis that explains their hydrogen-dependent metabolism to address the mitochondrion acquisition and subsequent endosymbiont processes. It has been proposed that the deduced last common ancestor was most likely a saline-adapted organism, and the evolutionary progression occurred most likely in the saline-to-freshwater direction, with few environmental transitional events. The major bathyarchaeotal community comprises Subgroups-1, -8, -12 and -15, and is relatively stable during the hypoxic/oxic change, thus being independent of the sedimentary chemistry change, such as manganese and iron redox cycling during different seasons (Devereuxetal.2015). Moreover, the carbonyl branch of the WoodLjungdahl pathway might reduce CO2 into acetyl-CoA. Uncultured archaea in deep marine subsurface sediments: have we caught them all? 2). The members of the Bathyarchaeota are the most abundant archaeal components of the transitional zone between the freshwater and saltwater benthic sediments along the Pearl River, with a central position within the co-occurrence network among other lineages (Liuetal.2014). Furthermore, evidence of fatty acid and aromatic compound utilization by Bathyarchaeota has been presented (Mengetal.2014; Evansetal.2015; Heetal.2016); these transformations would be supported by the beta-oxidation pathway and a potential anaerobic aromatic compound degradation pathway. WebArchaea are tiny, simple organisms. Furthermore, a principal coordinate analysis also clearly separates the bathyarchaeotal community into freshwater and saline sediment groups. Furthermore, genomic features of Subgroup-8 resolved from the metagenome of lignin-added enrichments evidence the putative lignin and aromatics degrading genes, thus it is hypothesized that Subgroup-8 catalyzes methoxy-groups of lignin, and combines the resulting methyl-group with CO2 to acetyl-coenzyme A (CoA) through the WoodLjungdahl pathway for either biosynthesis or acetogenesis in downstream pathways (Yuetal.2018). Oxford University Press is a department of the University of Oxford. The capability to utilize a wide variety of substrates might comprise an effective strategy for competing with substrate specialists for energy sources in various environments (Lietal.2015), such as detrital protein-rich deep seafloor sediments and estuarine sediments containing various carbohydrates. Eight subgroups were delineated based on the freshwater/saline segregation, as suggested by the significant IndVal values (P < 0.01) pointing to freshwater/marine sediment distribution. It is well known that isoprenoid glycerol dialkyl glycerol tetraether lipids are specifically synthesized by archaea. Tree building intermediate files are publicly available (https://github.com/ChaoLab/Bathy16Stree). The central product, acetyl-CoA, would either (i) be involved in substrate-level phosphorylation to generate acetate and ATP, catalyzed by an ADP-forming acetyl-CoA synthase as in other peptide-degrading archaea; (ii) be metabolized to generate acetate through the Pta-Ack pathway, similarly to bona fide bacterial homoacetogens; or (iii) be utilized for biosynthesis, e.g. Community, Distribution, and Ecological Roles WebInteresting Archaebacteria Facts: Archaebacteria are believed to have emerged approximately 3.5 billion years ago. Within Bathyarchaeota, the sequences were classified into six subclades according to . The three methods described above may be used for the quantification of bathyarchaeotal abundance based on DNA and RNA targets. 3B). Subgroup-5 is divided into Subgroups-5a and -5b, each with intragroup similarity >90% according to a maximum-likelihood estimation. The picked genomes are of high completeness (>70%) and good quality (excluding genomes with numerous long breaking parts with N). In summary, there are a total of 25 subgroups of Bathyarchaeota based on all available 16S rRNA gene sequences at this moment, and the former names for each subgroup are also labeled in the tree (Fig. Consequently, CO2 appears to be the only electron acceptor mediating AOM, like in a reverse acetoclastic methanogenesis (Hallametal.2004; Wangetal.2014). facts about bathyarchaeota Diverse Bathyarchaeotal Lineages Dominate Archaeal Bathyarchaeota, a recently proposed archaeal phylum, is globally distributed and highly abundant in anoxic sediments. No methane metabolism genes were recovered from bathyarchaeotal genomic bins or any contigs from the WOR estuarine sediments, in contrast to an earlier study (Evansetal.2015). These indicative subgroups are the dominant ones in the environment, as evaluated by relatively abundant fraction of Bathyarchaeota in corresponding archaeal communities (on average 44% among all studies). The distinct bathyarchaeotal subgroups diverged to adapt to marine and freshwater environments. These results have not only demonstrated multiple and important ecological functions of this archaeal phylum, but also paved the way for a detailed understanding of the evolution and metabolism of archaea as such. Regarding the functional properties, metabolic pathway analysis revealed that BA1 is a peptide and glucose fermenter, while BA2 is a fatty-acid oxidizer (Evansetal.2015). The Archaebacteria kingdom is divided into three Future efforts should be encouraged to address the fundamental issues of the diversity and distribution patterns of Bathyarchaeota, and their vital roles in global carbon cycling. Hallam SJ, Putnam N, Preston CM et al. In a recent study, Bathyarchaeota and ANME were shown to predominate on the flange of a hydrothermal chimney wall in the Soria Moria Vent field, where the local energy condition favors anaerobic methane oxidizers (Dahleetal.2015). Recently, two bathyarchaeotal genome bins (BA1 and BA2) were recovered from the formation waters of coal-bed methane wells within the Surat Basin (Evansetal.2015). (2016) reconstructed six nearly complete bathyarchaeotal genomes (Subgroups-13, -15, -16, -18 and -19) from the Guaymas Basin subsurface sediment. All assigned subgroups have minimum intra-group >90%, and are clustered into one clade with previously reported anchor sequences (Kuboetal.2012). Bathyarchaeota occupied about 60% of the total archaea in the Jiulong River, China (Li et al. 3C). Bathyarchaeota was the dominant archaeal taxon in the sediment samples from 3400 to 02 (40.67%) and CJ-00a (34.17%), which have the shallowest water Callac N, Rommevaux-Jestin C, Rouxel O et al. OTUs classified within Bathyarchaeota and Chloroflexi (Dehalococcoidia) showed positive correlation with methane concentrations, sediment depth and oxidation-reduction potential. According to the meta-analysis of archaeal sequences available in the ARB SILVA database (Kuboetal.2012), Bathyarchaeota was further recognized as a group of global generalists dwelling in various environments, including marine sediments, hydrothermal vents, tidal flat and estuary sediments, hypersaline sediments, terrestrial subsurface, biomats, limnic water and sediments, underground aquifers, hot springs, soils, municipal wastewaters, animal digestive tract, etc. Since these two genomic bins represent only a small fraction of all bathyarchaeotal lineages, and no evidence of methanogenic machinery is apparent in the recent parallel genomic binning data, the ability to metabolize methane might not be shared by all subgroup lineages (Lloydetal.2013; Mengetal.2014; Heetal.2016; Lazaretal.2016). Genomic characterization and metabolic potentials of Bathyarchaeota. The Miscellaneous Crenarchaeotal Group (MCG) archaea were firstly detected from a hot spring (Barnsetal.1996) and later proposed with a name in a study surveying 16S rRNA gene sequences from marine subsurface sediments (Inagakietal.2003). Details of markers refer to Supplementary Table S1 available online. Based on the genomic evidence, the authors concluded that some lineages of Bathyarchaeota are similar to bona fide bacterial homoacetogens, with pathways for acetogenesis and fermentative utilization of a variety of organic substrates (Heetal.2016). Peptidases targeting d-amino acids, which are highly enriched in the peptidoglycan of bacterial cell walls, are encoded as well, indicating that Bathyarchaeota may have acquired the capacity to degrade recalcitrant components of bacterial cell walls, i.e. In addition, some regions of the bathyarchaeotal genome might have been acquired from bacteria because of the aberrant tetranucleotide frequency in the genomic fragments of Bathyarchaeota and bacterial phylogenetic origins of these genomic fragments (Lietal.2012). Genomic expansion of archaeal lineages resolved from deep Here we provide several lines of converging evidence suggesting the bathyarchaeotal group Bathy-8 is able to grow with lignin as an energy source and The active microbial community in four SMTZ layers of the ODP Leg 201 subsurface sediment cores off Peru was dominated by MBG-B and Bathyarchaeota (Biddleetal.2006). Four genomes (Subgroups-1, -6, -7 and -15) were recovered from the sediment metagenome. Recently, Subgroup-15 was widely detected in both freshwater and marine benthic sediments; its persistent distribution along the sediment depth profile, with higher abundance within active archaeal communities, provides additional hints linking its members physiological traits to habitat preferences (Liuetal.2014). Phylogenetic tree of bathyarchaeotal 16S rRNA genes. Considering the relative abundance of lineages in the separated leaves, Bathyarchaeota accounted for the greatest proportion of lineage variance in the freshwater and saline environments. Members of the Bathyarchaeota, formerly known as the Miscellaneous Crenarchaeota Group (MCG), are widely distributed in various environments such as freshwater lake, marine, and estuarine sediments [ 18, 19, 20, 21 ]. Kallmeyer J, Pockalny R, Adhikari RR et al. No bathyarchaeotal species have as yet been successfully cultured in pure cultures, despite their widespread distribution in the marine, terrestrial and limnic environments (Kuboetal.2012), which hampers their direct physiological characterization. The clear growth stimulus and lignin-related 13C-bicarbonate incorporation into lipids strongly suggests that Bathyarchaeota (Subgroup-8) may be able to use the second-most abundant biopolymer lignin on Earth (Yuetal.2018). bathys, meaning deep as it locates deep branching with Thaumarchaeota and Aigarchaeaota, and frequently detected in the deep subsurface sediments; N.L. Lineage (full): cellular organisms; Archaea; TACK group. Kellermann MY, Wegener G, Elvert M et al. However, in a study investigating the archaeal lipidome in the White Oak River estuary, the presence of the recently discovered butanetriol dibiphytanyl glycerol tetraethers correlated well with bathyarchaeotal abundance along the sediment depth (Meadoretal.2015). Several sets of PCR primers and probes have been developed to detect and quantify Bathyarchaeota in natural community (Table 1). Furthermore, one new subgroup (Subgroup-23) was proposed in this study (Fig. (2016), it appears that these microbes rely on the acetyl-CoA synthetase (Acd) to generate acetate (Heetal.2016). Bathyarchaeota are believed to have roles in the carbon cycle in marine systems. To cover all bathyarchaeotal subgroups that are characterized by high intragroup diversity while retaining bathyarchaeotal sequence specificity is necessary but challenging. the census of energy availability for redox reactions, is used, to some extent, to constrain and predict the distribution of functional groups of chemotrophic microorganisms (Amendetal.2011; LaRowe and Amend 2014). A pair of primers (Bathy-442F/Bathy-644R) was recently designed to target Subgroups-15 and -17; the in silico primer testing indicates that Bathy-442F can also adequately cover Subgroups-2, -4, -9 and -14, with Bathy-644R covering nearly all subgroups, except for Subgroups-6 and -11 (Yuetal.2017). Introduction. Barns SM, Delwiche CF, Palmer JD et al. 3). The Distribution of Bathyarchaeota in Surface Sediments With respect to its function, the protein might be responsible for photosynthesis in archaea; this suggests that photosynthesis may have evolved before the divergence of the bacteria and archaea domains (Mengetal.2009; Lietal.2012). Td stands for dissociation temperature for RNA slot-bolt. Following the four treatments, the viable bathyarchaeotal communities mainly comprised Subgroups-4 and -8, thus indicating that these two subgroups could tolerate the initial aerobic conditions (Gagenetal.2013). This approach revealed that the separation of subgroups according to saline and anoxic levels could explain 13% of the phylogenetic lineage variance. Furthermore, the lack of genes for ATPases and membrane-bound electron transport enzymes in the two genomic bins (BA1 and BA2) and the presence of the ion pumping, energy-converting hydrogenase complex (only in BA1), which might allow solute transportation independently of energy-generation mechanisms, suggest that the soluble substrate transportation is solely responsible for energy conservation (Evansetal.2015). Bathyarchaeota was initially proposed to form a distinct cluster closely related to Aigarchaeota and hyperthermophilic Crenarchaeota; because of their terrestrial origin (Barnsetal.1996) (such as freshwater lakes and hot springs), the name Terrestrial MCG was temporarily proposed (Takaietal.2001). Further membrane lipid characterization of enriched or pure bathyarchaeotal cultures will help to validate this discovery. On the other hand, the subgroups MCG-18 and MCG-19 were also named in Fillol et al.s research (Filloletal.2016). Furthermore, both FISH labeling and intact polar lipid quantification suggest the presence of highly abundant and active bathyarchaeotal cells in the Peru offshore subsurface sediments collected during the Ocean Drilling Program Leg 201 (Biddleetal.2006; Lippetal.2008). Stahl DA, Flesher B, Mansfield HR et al. The discovery of BchG of archaeal origin in the genomic content of Bathyarchaeota also suggests that an archaeon-based photosynthetic pathway might exist in nature, and that photosynthesis might have evolved before the divergence of bacteria and archaea (Mengetal.2009). Other archaeal groups are also commonly detected in estuaries worldwide. Peat MCG group was represented with one sequence at 90% cutoff level (Xiangetal.2017). Summary. adj. Phylogenetic analysis of the Pta and Ack coding sequences in He et al.s study revealed that these genes form a monophyletic clade and are different from all other know sequences, indicating that they evolved independently of the currently known bacterial counterparts (Heetal.2016). Subgroups were assigned from the corresponding 16S rRNA gene phylogenic tree (Fig. Archaebacteria Facts - Softschools.com pl. On the other hand, the proportion of bathyarchaeotal sequence in the total archaeal community sequence increases with depth, and they may favor anoxic benthic sediments with iron-reducing conditions. The analysis of the stable isotopic-probed microcosms from Cheesequake salt marsh sediment revealed that all Crenarchaeota groups, which still include Bathyarchaeota and Thaumarchaeota (formerly Crenarchaeota MG 1.a) and other Crenarchaeota groups, are heterotrophic and do not incorporate 13C-bicarbonate (Seyler, McGuinness and Kerkhof 2014). However, Lokiarchaeota and most members of the Bathyarchaeota phylum lack the essential methane metabolizing elements, such as CoB or CoM synthase and methyl-CoM reductase, etc., though they use H4MPT as the C1-carrier, which is common in methanogens. This study is also a contribution to the Deep Carbon Observatory. Single amplified genomes (SAGs) of a Subgroup-15 bathyarchaeotal member from the Aarhus Bay sediments harbor genes for predicted extracellular protein degrading enzymes, such as clostripain (Lloydetal.2013). Archaea Definition & Meaning - Merriam-Webster This will have a profound impact not only on deciphering the metabolic properties of Bathyarchaeota, by using butanetriol dibiphytanyl glycerol tetraethers as biomarkers to trace carbon acquisition by isotopic labeling, but also by representing their pivotal contribution, associated with their global abundance, to biogeochemical carbon cycling on a large ecological scale. Here we reported the abundance of Bathyarchaeota members across different ecosystems and their correlation with environmental factors by constructing 16S The knowledge of their physiological and genomic properties, as well as their adaptive strategies in various eco-niches, is nonetheless still rudimentary. Laso-Prez R, Wegener G, Knittel K et al. In this process, methane is not assimilated by Bathyarchaeota but serves as an energy source. The use of MCG242dF resulted in an adequate coverage of almost all subgroups with 0/1 nucleotide mismatches, except for Subgroups-10 and -17, which showed low coverage efficiency with no nucleotide mismatches. Obtaining direct physiological evidence for the generation or oxidization of methane by Bathyarchaeota in the future is also important. Phylogenetic analyses of 16S rRNA gene sequences were inferred by Maximum Likelihood implemented in RAxML 8.0 on the CIPRES Science Gateway using the GTR+GAMMA model and RAxML halted bootstrapping automatically (Miller, Pfeiffer and Schwartz 2010; Stamatakis 2014). Bathyarchaeota, formerly known as the Miscellaneous Crenarchaeotal Group, is a phylum of global generalists that are widespread in anoxic sediments, which host relatively high abundance archaeal communities. After incubation with 13C-acetate, the archaeal population within a sulfate reduction zone, detected on the basis of 13C-DNA, was almost entirely dominated by Bathyarchaeota (65% by Subgroup-8 and 30% by Subgroup-15) (Websteretal.2010). Bathyarchaeota possesss a bona fide homoacetogenesis pathway of archaeal phylogenetic origin, as confirmed by functional studies, indicating a distinct evolutionary pathway of acetogenesis in archaea, different from horizontal transfer from bacteria (Heetal.2016). their relatively high abundance in the global marine subsurface ecosystem (Kuboetal.2012; Lloydetal.2013), they are also metabolically active in the subsurface sediments across geological time scales. with 12C-acetate added); this indicated that the acetate might participate in microbial biosynthesis rather than being used for energy production (Naetal.2015). The production of a putative 4-carboxymuconolactone decarboxylase was evident when the mangrove sediments were supplemented with protocatechuate, further suggesting the capacity of certain bathyarchaeotal members to degrade aromatic compounds (Mengetal.2014). Taxonomic classification revealed that between 0.1 and 2% of all classified sequences were assigned to Bathyarchaeota. More importantly, the first-ever bacteriochlorophyll a synthase (BchG) of archaeal origin was identified in the archaeal portion of the genomic fragment, and its function confirmed by producing BchG in a heterologous expression system (Mengetal.2009). Materials and methods 2.1. Furthermore, analysis of clone libraries retrieved after 13C-DNA amplification combined with matched terminal fragment length polymorphism peaks suggested that the heterotrophic bathyarchaeotal community possibly comprised Subgroups-6 and -8 (Seyler, McGuinness and Kerkhof 2014). Background Bathyarchaeota, a newly proposed archaeal phylum, is considered as an important driver of the global carbon cycle. Bathyarchaeota: globally distributed metabolic The deduced last common ancestor of Bathyarchaeota might be a saline-adapted organism, which evolved from saline to freshwater habitats during the diversification process, with the occurrence of few environmental transitional events. In some flange subsamples, Bathyarchaeota were even more dominant than ANME; however, compared with the well-studied metabolism of ANME, the exact function of Bathyarchaeota in that ecological setting remains unknown. Because of the high diversity of Bathyarchaeota and various independent analyses of samples from diverse environments, the nomenclature for this archaeal group in previous reports was very complex. In experiments towards cultivating Bathyarchaeota from the White Oak River estuary sediments, the abundance of Bathyarchaeota in control groups (basal medium) and in experimental groups containing various substrate additives and submitted to various culture processing steps were compared (Gagenetal.2013). Institute for Advanced Study, Shenzhen University, Shenzhen 518060, People's Republic of China, Laboratory of Environmental Microbiology and Toxicology, School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong SAR, People's Republic of China. Co-occurrence networks in the archaeal clone libraries indicated the role of Bathyarchaeota as keystone species, and suggested their function in maintaining the stability and adaptability of the archaeal community (Xiangetal.2017). Open reading frames encoded by the three fosmid clones comprised genes related to lipid biosynthesis, energy metabolism and resistance to oxidants. Fillol M, Snchez-Melsi A, Gich F et al. Gene arrangement in these two fosmid clones, together with the previously recovered bathyarchaeotal fosmid sequences, confirmed low collinearity with other known archaeal genomes. the potential AOM metabolism of Bathyarchaeota in the flange of the hydrothermal vent would be consistent with the aforementioned genomic inferences (Evansetal.2015). The diversity of bathyarchaeotal community turns out to be similar in the four cultivation treatments (basal medium, addition of an amino acid mix, H2-CO2 headspace and initial aerobic treatment). Newberry CJ, Webster G, Cragg BA et al. 3) (Lloydetal.2013; Evansetal.2015; Lazaretal.2015; Heetal.2016; Lazaretal.2016; Lever 2016). In one study, small amounts of stable isotope-labeled substrates, including glucose, acetate and CO2, were introduced multiple times into slurries from different biogeochemical depths of tidal sediments from the Severn estuary (UK) to better reflect the in situ environmental conditions (Websteretal.2010). The groups of B24 and B25 (Heetal.2016) were added into the tree representing Subgroups-21 and -22, respectively. Ta stands for qPCR annealing temperature, Ta,e stands for annealing and extension temperature of two-step qPCR. Recently, two more bathyarchaeotal fosmid clones were screened from estuarine mangrove sediments (Mengetal.2014). (2012) demonstrated that the developed primers and probes result in poor coverage of Subgroups-13 to -17. Furthermore, the MCR complexes found in the BA1 and BA2 genomes are phylogenetically divergent from traditional MCR and they coevolved as a whole functional unit, indicating that methane metabolism began to evolve before the divergence of the Bathyarchaeota and Euryarchaeota common ancestors (Evansetal.2015).
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