These physiological, ecological and evolutionary features place Bathyarchaeota in the spotlight of current microbial ecology studies, encouraging further explorations of their impact on global and local biogeochemical carbon cycling. 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). The IndVal species with statistical support in terrestrial environments indicated by this study were pMCG and Subgroup-5b in peat; Subgroup-5a in hot springs; Subgroup-6 in the soil; Subgroups-3, -4, -13 and -16 in estuaries; and Subgroup-15 in mangroves. Abstract. Subgroup-6 persists in such suboxic, sulfide-depleted shallow sediment layers, while Subgroups-1, -5 and -8 preferentially occur in deeper, more reducing subsurface layers (Lazaretal.2015). They include Euryarchaeota, and members of the DPANN and Asgard archaea. Genes responsible for the dissimilatory nitrite reduction to ammonium (nirB and nrfD) were identified in Subgroups-1, -17 (formally Subgroup-7/17), -6 and -15, respectively, suggesting the potential existence of a respiratory pathway involving nitrite reduction (Lazaretal.2016). (2008) further summarized 47 clone libraries of 16S rRNA genes from the marine subsurface, with Bathyarchaeota accounting for 33% of all archaea. 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. 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). Their results agree well and reflect the relatively higher bathyarchaeotal fraction in marine sediments with sulfate penetration (>0.15 m below seafloor) (Kuboetal.2012). Barns SM, Delwiche CF, Palmer JD et al. Archaea Definition & Meaning - Merriam-Webster To alleviate the nomenclature confusion, we constructed an updated RAxML tree (Fig. 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. Further, based on genomic inferences, Evansetal. The metabolic properties are also considerably diverse based on genomic analysis (Fig. 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). Four major heterotrophic pathways centralized on the acetyl-CoA generation are summarized below, reflecting the core metabolism of fermentation and acetogenesis (Fig. Given the diverse and complex phylogeny of the Bathyarchaeota (Kuboetal.2012; Filloletal.2016), the occurrence of commonly shared physiological and metabolic properties in different lineages seems unlikely, with the evolutionary diversification of bathyarchaeotal lineages largely driven by the adaptation to various environmental conditions and available carbon and energy sources, etc. Fosmid clone 37F10 containing a genome fragment originating from a bathyarchaeotal member was isolated from a metagenomic library constructed from Pearl River sediment samples (Mengetal.2009); its G + C content indicated that this genomic fragment had two portions: an archaeon-like portion (42.2%) and a bacterium-like portion (60.1%) (Mengetal.2009; Lietal.2012). The concatenated ribosomal protein (RP) alignment contained 12 RPs, and those genomes with <25% RPs were excluded from tree construction. 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). 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. Kallmeyer J, Pockalny R, Adhikari RR et al. It harbors methyl-coenzyme M reductase (MCR)-encoding genes, and many identified and unidentified methyltransferase-encoding genes for the utilization of various methylated compounds, but lacks most of the genes encoding the subunits of Na+-translocating methyl-H4MPT:coenzyme M methyltransferase, suggesting that the organism does not engage in hydrogenotrophic methanogenesis. Webarchaea: [plural noun] microorganisms of a domain (Archaea) including especially methane-producing forms, some red halophilic forms, and others of harsh hot acidic environments 2). Stahl DA, Flesher B, Mansfield HR et al. Within Bathyarchaeota, the sequences were classified into six subclades according to . 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). Collectively, these findings indicate a hybrid of archaeal and bacterial features for acetogenesis of Bathyarchaeota. Interestingly, one of the highly abundant McrA subunits of Ca. Consequently, CO2 appears to be the only electron acceptor mediating AOM, like in a reverse acetoclastic methanogenesis (Hallametal.2004; Wangetal.2014). Methane would be oxidized in a stepwise manner to methyl-tetrahydromethanopterin (CH3-H4MPT); the methyl group of CH3-H4MPT and CO2 would then be subjected to a CO dehydrogenase/acetyl-CoA synthase (CODH/ACS complex); CO2 would be fixed by a reverse CO dehydrogenation to CO, and then coupled with a methyl group and CoA to generate acetyl-CoA; ATP would be generated in the course of substrate-level phosphorylation from ADP, with one acetate molecule simultaneously generated by a reverse ADP-forming acetyl-CoA synthase. Metabolic potential of Bathyarchaeota and their interactive relationships with other microorganisms. Yuetal. (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 presence and relative abundance of bathyarchaeotal rRNA can then be estimated based on the hybridization intensity (Stahletal.1988; Kuboetal.2012). Beyond methane Bathyarchaeota are believed to have roles in the carbon cycle in marine systems. In addition, the catalyzed reporter deposition-fluorescent in situ hybridization (CARD-FISH) studies for the detection and quantification of bathyarchaeotal cells suggest that they are abundant in the center and marine invertebrate-inhabited layers in the Haakon Mosby Mud Volcano, and in the marine subsurface sediments in the Equatorial ODP site 1125 and Peru Basin ODP site 1231 (Kuboetal.2012). 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. 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. Materials and methods 2.1. Kellermann MY, Wegener G, Elvert M et al. They were originally discovered in extreme environments ( extremophiles ), but are now thought to be common to more average 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). The novel Bathyarchaeota lineage possesses an incomplete methanogenesis pathway lacking the methyl co-enzyme M reductase complex and encodes a non-canonical acetogenic pathway potentially coupling methylotrophy to acetogenesis via the methyl branch of Wood-Ljundahl pathway. Subgroup-5 thrives in the euxinic bottom water layer, characterized as anoxic and sulfide-rich, with accumulated inorganic and organic reduced compounds; Subgroup-6 is a group of generalists that are adapted to both planktonic and sediment habitats with a wide range of sulfidic conditions. The distinct bathyarchaeotal subgroups diverged to adapt to marine and freshwater environments. 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). 3). Because of the universal distribution and predominance of Bathyarchaeota, not only in the marine sediments but also in terrestrial sediments and various other eco-niches, and because of their versatile metabolism (including acetogenesis, methane metabolism, and dissimilatory nitrate and sulfate reduction) and potential interactions with ANME archaea, acetoclastic methanogens and heterotrophic bacteria, the ecological importance of this group of generalists has entered the limelight and needs further exploration. The results also revealed that some operational taxonomic units affiliated with Subgroups-2 and -15 are dominant in all surface and bottom sediment layers in these two cores, suggesting that these operational taxonomic units might be adaptive to redox changes (Yuetal.2017). High-throughput sequencing of the archaeal communities and the analysis of the relationship between the distribution pattern of bathyarchaeotal subgroups and the physicochemical parameters of study sites revealed that sediment depth and sulfate concentration were important environmental factors that shape the distribution of bathyarchaeotal subgroups; Subgroup-8 was shown to be predominantly distributed in the reducing and deeper sediment layers, while Subgroup-10 was preferentially distributed in the relatively more oxidizing and shallow sediment layers (Yuetal.2017). bathys, meaning deep as it locates deep branching with Thaumarchaeota and Aigarchaeaota, and frequently detected in the deep subsurface sediments; N.L. 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). 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). Bathyarchaeota A new phylum name for this group was proposed, i.e. Heetal. 2017KZDXM071), and the Science and Technology Innovation Committee of Shenzhen (Grant No. Taxonomic classification revealed that between 0.1 and 2% of all classified sequences were assigned to Bathyarchaeota. (2017) investigated the bathyarchaeotal community in two sediment cores from the South China Sea; the authors revealed a direct strong positive correlation between bathyarchaeotal 16S rRNA gene abundance and total organic carbon content along the core depth, suggesting an overall heterotrophic lifestyle of Bathyarchaeota in the South China Sea. 4) (Evansetal.2015; Heetal.2016; Lazaretal.2016). Introduction. Liu et al. Lineage (full): cellular organisms; Archaea; TACK group. Diverse Bathyarchaeotal Lineages Dominate Archaeal A detailed knowledge of the phylogenetic structure of the Bathyarchaeota phylum is crucial for the understanding of their ecological significance in global sedimentary processes. 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). 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). Methanogenesis and acetogenesis are considered to be the two most fundamental and ancient microbial biochemical energy conservation processes, and they both employ the WoodLjungdahl pathway for CO2 reduction and ATP generation (Weissetal.2016). On the other hand, the subgroups MCG-18 and MCG-19 were also named in Fillol et al.s research (Filloletal.2016). Zhichao Zhou, Jie Pan, Fengping Wang, Ji-Dong Gu, Meng Li, Bathyarchaeota: globally distributed metabolic generalists in anoxic environments, FEMS Microbiology Reviews, Volume 42, Issue 5, September 2018, Pages 639655, https://doi.org/10.1093/femsre/fuy023. Considering the bathyarchaeotal community structure, depth is the first variable responsible for the high degree of absolute subgroup separation, followed by sulfide concentration (reflecting the redox conditions), which is responsible for a low degree of subgroup separation (Lazaretal.2015). 2). More recently, the proposed genus Candidatus Syntrophoarchaeum was shown to be able to anaerobically oxidize butane in a manner similar to ANME oxidation of methane, by reverse methanogenesis, a process that is initially mediated by MCR (Laso-Prezetal.2016). Vertical Distribution of Bathyarchaeotal Communities in The emergence of freshwater-adapted lineages, including freshwater-indicative Subgroups-5, -7, -9 and -11, occurred after the first salinefreshwater transition event (Filloletal.2016). Newberry CJ, Webster G, Cragg BA et al. Based on the phylogenetic analysis of concatenated rRNA, ribosome proteins and topomerase IB protein-encoding genes, MCG is phylogenetically distinct from the closely related Aigarchaeota and Thaumarchaeota, and comprises a parallel lineage that has perhaps evolved from a common ancestor (Mengetal.2014). pl. Kubo et al. Y He, et al., Genomic and enzymatic evidence for acetogenesis among multiple lineages of the archaeal phylum Bathyarchaeota widespread in marine sediments. Nat Microbiol 1, 16035 (2016). L Jiang, Y Zheng, J Chen, X Xiao, F Wang, Stratification of achaeal communities in shallow sediments of the Pearl River Estuary, Southern China. The uptake and breakdown of polymeric hydrocarbons is facilitated by extracellular hydrolases; Bathyarchaeota also acquired the EmbdenMeyerhof Parnas/EntnerDoudoroff glycolysis and gluconeogenesis pathway for the core hydrocarbon utilization metabolism. 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). (2015) presumed the syntrophy between Bathyarchaeota and sulfate-reducing bacteria (SRB) toward anaerobic oxidation of methane (AOM) (Evansetal.2015). 3) (Lloydetal.2013; Evansetal.2015; Lazaretal.2015; Heetal.2016; Lazaretal.2016; Lever 2016). 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. adj. S. butanivorans protein extracts; they are probably responsible for the initial step of butane activation to generate butyl-CoM. Both Bathyarchaeota and the recently identified more basally branched Lokiarchaeota acquired the H4MPT-dependent WoodLjungdahl pathway and the hydrogen-dependent electron bifurcating system MvhADG-HdrABC, viewed as typical for the anaerobic and hydrogen-dependent archaeal lifestyle (Lazaretal.2016; Sousaetal.2016). WebGiven the wide environmental and phylogenetic diversity of Bathyarchaeota, additional genomes are required to understand the metabolic capabilities of this understudied Subgroup-5 is divided into Subgroups-5a and -5b, each with intragroup similarity >90% according to a maximum-likelihood estimation. Sequences longer than 940 bp were first used to construct the backbone of the tree, and additional sequences were then added without altering the general tree topology. Viral Host. Bathyarchaeota Occurrence in Shallow Marine Methane 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). Moreover, the carbonyl branch of the WoodLjungdahl pathway might reduce CO2 into acetyl-CoA. 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. Based on the physiological and genomic evidence, acetyl-coenzyme A-centralized heterotrophic pathways of energy conservation have been proposed to function in Bathyarchaeota; these microbes are able to anaerobically utilize (i) detrital proteins, (ii) polymeric carbohydrates, (iii) fatty acids/aromatic compounds, (iv) methane (or short chain alkane) and methylated compounds, and/or (v) potentially other organic matter. Diverse Bathyarchaeotal Lineages Dominate Archaeal 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). 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. In contrast, Subgroup-15 (Crenarchaeota group C3) organisms dominate cDNA libraries from all sediment layers, albeit with minor contribution to the corresponding DNA libraries; this indicates that this group is metabolically active in the benthic euxinic, organic-rich sediments of karstic lakes (Filloletal.2015). Diverse Bathyarchaeotal Lineages Dominate Archaeal A phylogenetic tree based on the sequences of UbiA prenyltransferase superfamily proteins, including ChlG/BchG and additional five subfamilies of this superfamily, revealed that this unique BchG of archaeal origin groups within the ChlG/BchG family; however, it diverged earlier than the bacterial BchG proteins. This could be explained by the versatile pathways of organic matter assimilation present in the majority of Bathyarchaeota, reflected by inferences from genomic data. It was proposed that the high diversity of Bathyarchaeota implies a high metabolic diversity among its subgroups (Kuboetal.2012). 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).
