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). facts about bathyarchaeota The Distribution of Bathyarchaeota in Surface Sediments Based on the lineage distribution pattern analysis of the archaeal community of seven major eco-niches, it is also evident that the different evolutionary lineages are habitat-specific, and salinity rather than temperature is the primary driving force of the variation of global archaea distribution, with a similar pattern also evident for the global bacterial distribution (Lozupone and Knight 2007; Auguet, Barberan and Casamayor 2010). 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). 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. Heetal. To compare the coverage and specificity of analysis using the qPCR primer pairs MCG242dF/MCG678R and MCG528F/MCG732R for freshwater and marine sediment samples, amplicons obtained with these two primer pairs were analyzed and community structures compared (Filloletal.2015). During the enriching process with lignin addition, the Subgroup-8 abundance climbed over 10 times compared with the initial stage and became the most dominant archaeal species. Fillol M, Auguet J-C, Casamayor EO et al. 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). Considering that the marine subseafloor environment is one of the largest reservoirs of the prokaryotic biomass on Earth, with an estimated microbial abundance of 2.9 1029 cells and harboring ca 9.131.5% of all prokaryotes on Earth (Kallmeyeretal.2012), the predominance and activity of Bathyarchaeota in the marine subsurface sediments indicates that these microbes might play a crucial role in global biogeochemical nutrient cycling. 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. [43] (Figure 4). 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. 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). (Fig. Capella-Gutirrez S, Silla-Martnez JM, Gabaldn T. Coolen MJL, Cypionka H, Sass AM et al. 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). The indicator subgroups in saline and freshwater sediments were depicted accordingly. Furthermore, another study demonstrated that the archaeal communities of the sulfatemethane transition zone at diffusion-controlled sediments of Aarhus Bay (Denmark) contain considerable amounts of Bathyarchaeota; the overall archaeal community structure did not change greatly during the experimentits diversity was lower after 6 months of incubation under heterotrophic conditions, with periodic modest sulfate and acetate additions (Websteretal.2011). WebInteresting Archaebacteria Facts: Archaebacteria are believed to have emerged approximately 3.5 billion years ago. The inset table shows the distribution of subgroups in major environmental categories. 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). 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 (ii) Similar 13C signatures of the archaeal biomass and total organic carbon suggest that the organic matter assimilation contributes to the bulk of the archaeal biomass; the relatively small 13C signature of the archaeal biomass in comparison with the dissolved inorganic carbon suggests that only a small amount of archaeal biomass is derived from autotrophic CO2 fixation (Biddleetal.2006). The energy landscape of a local environment, i.e. A segregated distribution of bathyarchaeotal subgroups was also observed in the water column and sediments in freshwater karstic lakes (Filloletal.2015). BA1 (Subgroup-3) genome contains many genes of the reductive acetyl-CoA (WoodLjungdahl) pathway and key genes of the methane metabolism pathway. The emergence of freshwater-adapted lineages, including freshwater-indicative Subgroups-5, -7, -9 and -11, occurred after the first salinefreshwater transition event (Filloletal.2016). Similarly, rRNA slot blot hybridization indicates the existence of functionally active Bathyarchaeota not only in the surface and subsurface sediments from the Nyegga site 272-02, Cascadia Margin, Gulf of Mexico, Hydrate Ridge ODP site 1245 and Janssand (North Sea), but also in the oxic mats in the Arabian Gulf and subsurface White Oak River sediments (Kuboetal.2012). The syntrophic relationship between Bathyarchaeota and SRB would be similar to the anaerobic methane-oxidizing archaea (ANME)/SRB consortium, and acetate would be maintained at a low level as a transient intermediate (Boetiusetal.2000; Hinrichs and Boetius 2002). In the case of Subgroup-15, which branched away from other groups, MCG242dF would be associated with a relatively low coverage efficiency in the absence of nucleotide mismatches, but high (above 80%) coverage efficiency with 1 or 2 nucleotide mismatches; similarly, MCG678R would be associated with a limited coverage efficiency in the absence of nucleotide mismatches, but the coverage efficiency increases considerably with 1 or 2 nucleotide mismatches. The metabolic properties are also considerably diverse based on genomic analysis (Fig. It was proposed that reduced ferredoxin generated by peptide and/or glucose might be used for the reduction of methyl groups on methylated compounds to subsequently generate methane (Evansetal.2015). n. Bathyarchaeota Gender: neuter Low collinear regions were found between bathyarchaeotal and reported archaeal genomic fragments, suggesting that the gene arrangement of Bathyarchaeota is distinct from that of sequenced archaea. 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 This is the first ever genomic evidence for homoacetogenesis, the ability to solely utilize CO2 and H2 to generate acetate, in an archaeal genome and of distinct archaeal phylogenetic origin other than that of Bacteria (Heetal.2016). The branching order of Subgroups-13 to -17 was unstable when analyzed by different tree-construction methods, and they were presented as multifurcated branches. lipid and amino acid synthesis (Fig. The Archaebacteria kingdom is divided into three 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). S. butanivorans protein extracts; they are probably responsible for the initial step of butane activation to generate butyl-CoM. They include Euryarchaeota, and members of the DPANN and Asgard archaea. Fryetal. Furthermore, in contrast to the consistent vertical distribution of all archaeal lineages in freshwater sediments with almost no abundance changes, the total abundance of all Bathyarchaeota and the fraction of Subgroup-15 increase along with the depths of sediments, with significantly high abundance within the archaeal community (Liuetal.2014). In the White Oak River estuary, the abundance of Bathyarchaeota decreases with decreasing reductive redox conditions of the sediment (Lazaretal.2015). The group was termed miscellaneous because of its occurrence in diverse habitats; it is not only abundant in marine sediments but is also widely distributed in terrestrial, freshwater, hot spring, hydrothermal, etc., environments (Kuboetal.2012). Subsequent heterologous expression of bathyarchaeotal Ack revealed that the enzyme can catalyze the biochemical reaction in the direction from acetyl phosphate to acetate, with a higher affinity for the substrates than the products (Heetal.2016). Bathyarchaeota was the most dominant archaeal taxa with 108 nodes and 501 edges in the network. 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. A model based on the thermodynamic considerations of chemicals and temperatures may be used to offer a framework linking the distribution of microbial groups and energy landscapes (Amendetal.2011; LaRowe and Amend 2014; Dahleetal.2015). Bathyarchaeota, a recently proposed archaeal phylum, is globally distributed and highly abundant in anoxic sediments. Td stands for dissociation temperature for RNA slot-bolt. More recently, Heetal. This could be explained by the versatile pathways of organic matter assimilation present in the majority of Bathyarchaeota, reflected by inferences from genomic data. In a recent global evaluation of the archaeal clone libraries from various terrestrial environmental settings, permutational analysis that tested the relationship between Bathyarchaeota and environmental factors suggested that salinity, total organic carbon and temperature are the most influential factors impacting community distribution across different terrestrial habitats (Xiangetal.2017). The phylum Bathyarchaeota, which has high species and functional diversity, is abundant and widespread in marine sediments. Inagaki F, Nunoura T, Nakagawa S et al. Liu et al. This suggests that methane metabolism might have evolved before the divergence of the ancient archaeal lineages of Bathyarchaeota and Euryarchaeota, in agreement with the assumption that methanogenesis might represent one of the earliest metabolic transformations (Battistuzzi, Feijao and Hedges 2004; Ferry and House 2006; Evansetal.2015; Lloyd 2015). However, the ecological knowledge of Bathyarchaeota is limited in peatland ecosystems. This method has been used to target the bathyarchaeotal 16S rRNA gene with specific probes, providing information on the active bathyarchaeotal community without culturing (Table 1). A successful enrichment, with nearly pure biomass of certain subgroups of Bathyarchaeota, would enable a more efficient investigation of their metabolic capacities using stable isotope-labeled substrates, and establishing a direct link between the genotype and phenotype. Based on the ancestral analysis, the phylum Bathyarchaeota is suggested to have a hot origin. Taken together, these findings are further steps toward the elucidation of the origin, evolution, and roles of Bathyarchaeota, a globally important archaeal phylum. Recent genomic evidence suggests that Bathyarchaeota might potentially be involved in methane metabolism, a property that had only been confirmed to date in the Euryarchaeota domain (Evansetal.2015; Lloyd 2015). Genomic fragments of the fosmid clone 75G8 harbor a putative methyl-accepting chemotaxis protein- and 4-carboxymuconolactone decarboxylase-encoding genes, suggesting that this bathyarchaeotal member (Subgroup-8) is able to utilize aromatic compounds. The phylogenetic species variability index, which reflects the phylogenetic relatedness of sequences originating from specific environments, suggests a non-random distribution of Bathyarchaeota assemblages in natural environments (Filloletal.2016). 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. (Kuboetal.2012), and the outgroup sequences of Crenarchaeota, YNPFFA group and Korarchaeota were added. Vertical Distribution of Bathyarchaeotal Communities in Subgroup-5b was further split into 5b and 5bb, as additional sequences were added. The gene for cytoplasmic flavin adenine dinucleotide-containing dehydrogenase (glcD) co-located with hdrD, indicating that BA1 uses lactate to reduce heterodisulfide in methanogenesis. Taxonomic classification revealed that between 0.1 and 2% of all classified sequences were assigned to Bathyarchaeota. The evidence for the presence of respiratory metabolism in other bathyarchaeotal subgroups is ambiguous although it cannot be excluded (Lazaretal.2016). (i) The 13C signature of the archaeal biomass suggests that only a small fraction of local archaea in SMTZ utilize methane, which might be explained by the contribution of Bathyarchaeota in the biomass; until now, only one line of evidence points to the acquisition of methane metabolism by Bathyarchaeota (Lloydetal.2013; Evansetal.2015; Lazaretal.2015; Heetal.2016). BA1 also lacks other genes for energy-conserving complexes, including F420H2 dehydrogenase, energy-converting hydrogenases A and B, Rhodobacter nitrogen fixation complex and V/A-type ATP synthase. 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). WebArchaea are tiny, simple organisms. 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). Devereux R, Mosher JJ, Vishnivetskaya TA et al. RNA slot blot hybridization can also be used for the quantification of functionally active bathyarchaeotal 16S rRNA. 1) (Heetal.2016; Lazaretal.2016). 2). However, because of the high intragroup diversity and potential heterogeneous metabolic properties and adaptive strategies within the bathyarchaeotal subgroups, investigation into the subgroup distribution patterns at a fine-sorted phylotype level was recommended. This approach revealed that the separation of subgroups according to saline and anoxic levels could explain 13% of the phylogenetic lineage variance. Genomic expansion of archaeal lineages resolved from deep 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). Surprisingly, these genes fall closely to the Bathyarchaeota mcr genes. CARD-FISH can be utilized for the detection, identification and enumeration of microorganisms in various environments, independently of culturing (Kubota 2013). However, according to the genomic information on most archaeal acetogens and bathyarchaeotal genomic bins obtained by Lazaretal. Diversity, metabolism and cultivation of archaea As suggested by the classification of uncultured archaea based on nearly full-length 16S rRNA gene sequences, the bathyarchaeotal sequence boundary falls into the minimum sequence identity range of phylum level (74.9579.9%), and each subgroup generally falls into the median sequence identity range of family and order levels (91.6592.9% and 88.2590.1%, respectively) (Yarzaetal.2014). The 13C-depleted nature of butanetriol dibiphytanyl glycerol tetraethers found in the study implied that members of Bathyarchaeota might be autotrophs or fueled by 13C-depleted organic substrates (Meadoretal.2015). In addition to the global distribution, expanding prokaryotic community investigations of deep ocean drilling sediments revealed that members of Bathyarchaeota occupy considerable fractions of the archaeal communities (Teske 2006). The metagenomic binning of WOR estuarine sediment DNA led to the reconstruction of draft genomes of four widespread Bathyarchaeota, with the genome completeness in the range of 4898% (Lazaretal.2016). bathyarchaeota Thaumarchaeota MG-I was present in the 12C-DNA library in the corresponding zone but was not detected in the 13C-DNA library, suggesting that these microbes are not able to use 13C-acetate (Websteretal.2010). Markers for individual pathway/function were scanned against genomes using the HMM and KEGG databases (Anantharamanetal.2016; Kanehisa, Sato and Morishima 2016; Spang, Caceres and Ettema 2017). 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). The assignment of bathyarchaeotal subgroups was made based on either having been formerly defined or being monophyletic, using both distance and maximum-likelihood estimations (Kuboetal.2012). (A) Phylogenetic tree of ribosomal proteins obtained from currently available bathyarchaeotal genomes (from GenBank, 29 November 2017 updated). On the other hand, the subgroups MCG-18 and MCG-19 were also named in Fillol et al.s research (Filloletal.2016). A recent study found that the refractory aromatic polymer lignin stimulated the growth of Bathyarchaeota (Subgroup-8) and they incorporated CO2 as a carbon source autotrophically and utilized lignin as an energy source (Yuetal.2018). Together with evidence of few phylogenetic changes throughout the incubation, it was suggested that the microbial community detected by stable isotopic probing could serve well in reflecting the metabolically active components. Obtaining direct physiological evidence for the generation or oxidization of methane by Bathyarchaeota in the future is also important. Recently, another meta-analysis using newly acquired global sediment bathyarchaeotal sequences resulted in the addition of two more subgroups, Subgroups-18 and -19, with high bootstrap supporting values (96% and 86%, respectively) (Filloletal.2016). The reconstructed bathyarchaeotal genomes (except for Subgroup-15) also encode proteins with the ability to import extracellular carbohydrates. This primer pair shows good specificity toward Bathyarchaeota; it allowed amplification of 10100 times more bathyarchaeotal 16S rRNA gene sequences from the sediment samples from the South China Sea, and the Atlantic and Antarctic Oceans than the MCG242dF/MCG678R primers (Yuetal.2017). Bathyarchaeota 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). 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. Beyond methane Bathyarchaeota: New Deep-Sea Methane-Consuming 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. Genomic inferences from SAGs and genome-resolved metagenomic bins provide further genomic support for the heterotrophic lifestyle of Bathyarchaeota, rendering them capable of adapting to various environments and becoming one of the most successful lineages globally (Fig.