The Thaumarchaeota: an emerging view of their phylogeny and ecophysiology

Prokaryotic community assembly patterns and nitrogen metabolic potential in oxygen minimum zone of Yangtze Estuary water column

It is predicted that oxygen minimum zones (OMZs) in the ocean will expand as a consequence of global warming and environmental pollution. This will affect the overall microbial ecology and microbial nitrogen cycle. As one of the world's largest alluvial estuaries, the Yangtze Estuary has exhibited a seasonal OMZ since the 1980s. In this study, we have uncovered the microbial composition, the patterns of community assembly and the potential for microbial nitrogen cycling within the water column of the Yangtze Estuary, with a particular focus on OMZ. Based on the 16 S rRNA gene sequencing, a specific spatial variation in the composition of prokaryotic communities was observed for each water layer, with the Proteobacteria (46.1%), Bacteroidetes (20.3%), and Cyanobacteria (10.3%) dominant. Stochastic and deterministic processes together shaped the community assembly in the water column. Further, pH was the most important environmental factor influencing prokaryotic composition in the surface water, followed by silicate, PO43-, and distance offshore (p < 0.05). Water depth, NH4+, and PO43- were the main factors in the bottom water (p < 0.05). At last, species analysis and marker gene annotation revealed candidate nitrogen cycling performers, and a rich array of nitrogen cycling potential in the bottom water of the Yangtze Estuary. The determined physiochemical parameters and potential for nitrogen respiration suggested that organic nitrogen and NO3- (or NO2-) are the preferred nitrogen sources for microorganisms in the Yangtze Estuary OMZ. These findings are expected to advance research on the ecological responses of estuarine oxygen minimum zones (OMZs) to future global climate perturbations.

Mineralogical and microbial characterization of alkali hot spring microbial mats and deposits in Pong Dueat Pa Pae hot spring, Northern Thailand

Hot spring environments encompass broad physicochemical ranges, in which temperature and pH account for crucial factors shaping hot spring microbial community and diversity. However, the presence of photosynthetic microbial mats adjacent to boiling hot spring vents, where fluid temperatures extend beyond photosynthetic capability, questions the microbial profiles and the actual temperatures of such adjacent mats. Therefore, this study aims to characterize thermophilic microbial communities at Pong Dueat Pa Pae hot spring using next-generation sequencing, including investigating hot spring mineralogy. Results suggest that Pong Dueat Pa Pae hot spring precipitates comprise mainly silica which also acts as the main preservative medium for microbial permineralization. Molecular results revealed the presence of cyanobacterial and Chloroflexi species in the thick, orange and green subaerial mats surrounding the vents, suggesting the mats would be at least 30 °C cooler than source vents despite constantly receiving geyser splashes. Bacterial abundance was considerably higher than archaeal (97.9% versus 2.1%). Cyanobacterial (mainly Synechococcus and Leptolygbya) and Chloroflexi species (mainly Roseiflexus) accounted for almost half (40.04%) of the bacterial community, while DHVEG-6 and Thaumarchaeota comprised dominant members (> 90%) of the archaeal fraction. This study updates and provides insights into thermophilic microbial community composition and mineralogy of hot springs in Thailand.

Ammonia-oxidizing archaea adapted better to the dark, alkaline oligotrophic karst cave than their bacterial counterparts

Subsurface karst caves provide unique opportunities to study the deep biosphere, shedding light on microbial contribution to elemental cycling. Although ammonia oxidation driven by both ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) is well explored in soil and marine environments, our understanding in the subsurface biosphere still remained limited to date. To address this gap, weathered rock and sediment samples were collected from the Xincuntun Cave in Guilin City, an alkaline karst cave, and subjected to high-throughput sequencing and quantification of bacterial and archaeal amoA, along with determination of the potential nitrification rates (PNR). Results revealed that AOA dominated in ammonia oxidation, contributing 48-100% to the PNR, and AOA amoA gene copies outnumbered AOB by 2 to 6 orders. Nitrososphaera dominated in AOA communities, while Nitrosopira dominated AOB communities. AOA demonstrated significantly larger niche breadth than AOB. The development of AOA communities was influenced by deterministic processes (50.71%), while AOB communities were predominantly influenced by stochastic processes. TOC, NH4+, and Cl- played crucial roles in shaping the compositions of ammonia oxidizers at the OTU level. Cross-domain co-occurrence networks highlighted the dominance of AOA nodes in the networks and positive associations between AOA and AOB, especially in the inner zone, suggesting collaborative effort to thrive in extreme environments. Their high gene copies, dominance in the interaction with ammonia oxidizing bacteria, expansive niche breadth and substantial contribution to PNR collectively confirmed that AOA better adapted to alkaline, oligotrophic karst caves environments, and thus play a fundamental role in nitrogen cycling in subsurface biosphere.

Metagenomic characterization of a novel non-ammonia-oxidizing Thaumarchaeota from hadal sediment

BACKGROUND

The hadal sediment, found at an ocean depth of more than 6000 m, is geographically isolated and under extremely high hydrostatic pressure, resulting in a unique ecosystem. Thaumarchaeota are ubiquitous marine microorganisms predominantly present in hadal environments. While there have been several studies on Thaumarchaeota there, most of them have primarily focused on ammonia-oxidizing archaea (AOA). However, systematic metagenomic research specifically targeting heterotrophic non-AOA Thaumarchaeota is lacking.

RESULTS

In this study, we explored the metagenomes of Challenger Deep hadal sediment, focusing on the Thaumarchaeota. Functional analysis of sequence reads revealed the potential contribution of Thaumarchaeota to recalcitrant dissolved organic matter degradation. Metagenome assembly binned one new group of hadal sediment-specific and ubiquitously distributed non-AOA Thaumarchaeota, named Group-3.unk. Pathway reconstruction of this new type of Thaumarchaeota also supports heterotrophic characteristics of Group-3.unk, along with ABC transporters for the uptake of amino acids and carbohydrates and catabolic utilization of these substrates. This new clade of Thaumarchaeota also contains aerobic oxidation of carbon monoxide-related genes. Complete glyoxylate cycle is a distinctive feature of this clade in supplying intermediates of anabolic pathways. The pan-genomic and metabolic analyses of metagenome-assembled genomes belonging to Group-3.unk Thaumarchaeota have highlighted distinctions, including the dihydroxy phthalate decarboxylase gene associated with the degradation of aromatic compounds and the absence of genes related to the synthesis of some types of vitamins compared to AOA. Notably, Group-3.unk shares a common feature with deep ocean AOA, characterized by their high hydrostatic pressure resistance, potentially associated with the presence of V-type ATP and di-myo-inositol phosphate syntheses-related genes. The enrichment of organic matter in hadal sediments might be attributed to the high recruitment of sequence reads of the Group-3.unk clade of heterotrophic Thaumarchaeota in the trench sediment. Evolutionary and genetic dynamic analyses suggest that Group-3 non-AOA consists of mesophilic Thaumarchaeota organisms. These results indicate a potential role in the transition from non-AOA to AOA Thaumarchaeota and from thermophilic to mesophilic Thaumarchaeota, shedding light on recent evolutionary pathways.

CONCLUSIONS

One novel clade of heterotrophic non-AOA Thaumarchaeota was identified through metagenome analysis of sediments from Challenger Deep. Our study provides insight into the ecology and genomic characteristics of the new sub-group of heterotrophic non-AOA Thaumarchaeota, thereby extending the knowledge of the evolution of Thaumarchaeota. Video Abstract.

Functional prediction of proteins from the human gut archaeome

The human gastrointestinal tract contains diverse microbial communities, including archaea. Among them, Methanobrevibacter smithii represents a highly active and clinically relevant methanogenic archaeon, being involved in gastrointestinal disorders, such as inflammatory bowel disease and obesity. Herein, we present an integrated approach using sequence and structure information to improve the annotation of M. smithii proteins using advanced protein structure prediction and annotation tools, such as AlphaFold2, trRosetta, ProFunc, and DeepFri. Of an initial set of 873 481 archaeal proteins, we found 707 754 proteins exclusively present in the human gut. Having analysed archaeal proteins together with 87 282 994 bacterial proteins, we identified unique archaeal proteins and archaeal-bacterial homologs. We then predicted and characterized functional domains and structures of 73 unique and homologous archaeal protein clusters linked the human gut and M. smithii. We refined annotations based on the predicted structures, extending existing sequence similarity-based annotations. We identified gut-specific archaeal proteins that may be involved in defense mechanisms, virulence, adhesion, and the degradation of toxic substances. Interestingly, we identified potential glycosyltransferases that could be associated with N-linked and O-glycosylation. Additionally, we found preliminary evidence for interdomain horizontal gene transfer between Clostridia species and M. smithii, which includes sporulation Stage V proteins AE and AD. Our study broadens the understanding of archaeal biology, particularly M. smithii, and highlights the importance of considering both sequence and structure for the prediction of protein function.

Scaling of Protein Function across the Tree of Life

Scaling laws are a powerful way to compare genomes because they put all organisms onto a single curve and reveal nontrivial generalities as genomes change in size. The abundance of functional categories across genomes has previously been found to show power law scaling with respect to the total number of functional categories, suggesting that universal constraints shape genomic category abundance. Here, we look across the tree of life to understand how genome evolution may be related to functional scaling. We revisit previous observations of functional genome scaling with an expanded taxonomy by analyzing 3,726 bacterial, 220 archaeal, and 79 unicellular eukaryotic genomes. We find that for some functional classes, scaling is best described by multiple exponents, revealing previously unobserved shifts in scaling as genome-encoded protein annotations increase or decrease. Furthermore, we find that scaling varies between phyletic groups at both the domain and phyla levels and is less universal than previously thought. This variability in functional scaling is not related to taxonomic phylogeny resolved at the phyla level, suggesting that differences in cell plan or physiology outweigh broad patterns of taxonomic evolution. Since genomes are maintained and replicated by the functional proteins encoded by them, these results point to functional degeneracy between taxonomic groups and unique evolutionary trajectories toward these. We also find that individual phyla frequently span scaling exponents of functional classes, revealing that individual clades can move across scaling exponents. Together, our results reveal unique shifts in functions across the tree of life and highlight that as genomes grow or shrink, proteins of various functions may be added or lost.

Microbial tapestry of the Shulgan-Tash cave (Southern Ural, Russia): influences of environmental factors on the taxonomic composition of the cave biofilms

BACKGROUND

Cave biotopes are characterized by stable low temperatures, high humidity, and scarcity of organic substrates. Despite the harsh oligotrophic conditions, they are often inhabited by rich microbial communities. Abundant fouling with a wide range of morphology and coloration of colonies covers the walls of the Shulgan-Tash cave in the Southern Urals. This cave is also famous for the unique Paleolithic painting discovered in the middle of the last century. We aimed to investigate the diversity, distribution, and potential impact of these biofilms on the cave's Paleolithic paintings, while exploring how environmental factors influence the microbial communities within the cave.

RESULTS

The cave's biofilm morphotypes were categorized into three types based on the ultrastructural similarities. Molecular taxonomic analysis identified two main clusters of microbial communities, with Actinobacteria dominating in most of them and a unique "CaveCurd" community with Gammaproteobacteria prevalent in the deepest cave sections. The species composition of these biofilms reflects changes in environmental conditions, such as substrate composition, temperature, humidity, ventilation, and CO2 content. Additionally, it was observed that cave biofilms contribute to biocorrosion on cave wall surfaces.

CONCLUSIONS

The Shulgan-Tash cave presents an intriguing example of a stable extreme ecosystem with diverse microbiota. However, the intense dissolution and deposition of carbonates caused by Actinobacteria pose a potential threat to the preservation of the cave's ancient rock paintings.

Diversity and taxonomic revision of methanogens and other archaea in the intestinal tract of terrestrial arthropods

Methane emission by terrestrial invertebrates is restricted to millipedes, termites, cockroaches, and scarab beetles. The arthropod-associated archaea known to date belong to the orders Methanobacteriales, Methanomassiliicoccales, Methanomicrobiales, and Methanosarcinales, and in a few cases also to non-methanogenic Nitrososphaerales and Bathyarchaeales. However, all major host groups are severely undersampled, and the taxonomy of existing lineages is not well developed. Full-length 16S rRNA gene sequences and genomes of arthropod-associated archaea are scarce, reference databases lack resolution, and the names of many taxa are either not validly published or under-classified and require revision. Here, we investigated the diversity of archaea in a wide range of methane-emitting arthropods, combining phylogenomic analysis of isolates and metagenome-assembled genomes (MAGs) with amplicon sequencing of full-length 16S rRNA genes. Our results allowed us to describe numerous new species in hitherto undescribed taxa among the orders Methanobacteriales (Methanacia, Methanarmilla, Methanobaculum, Methanobinarius, Methanocatella, Methanoflexus, Methanorudis, and Methanovirga, all gen. nova), Methanomicrobiales (Methanofilum and Methanorbis, both gen. nova), Methanosarcinales (Methanofrustulum and Methanolapillus, both gen. nova), Methanomassiliicoccales (Methanomethylophilaceae fam. nov., Methanarcanum, Methanogranum, Methanomethylophilus, Methanomicula, Methanoplasma, Methanoprimaticola, all gen. nova), and the new family Bathycorpusculaceae (Bathycorpusculum gen. nov.). Reclassification of amplicon libraries from this and previous studies using this new taxonomic framework revealed that arthropods harbor only CO2 and methyl-reducing hydrogenotrophic methanogens. Numerous genus-level lineages appear to be present exclusively in arthropods, suggesting long evolutionary trajectories with their termite, cockroach, and millipede hosts, and a radiation into various microhabitats and ecological niches provided by their digestive tracts (e.g., hindgut compartments, gut wall, or anaerobic protists). The distribution patterns among the different host groups are often complex, indicating a mixed mode of transmission and a parallel evolution of invertebrate and vertebrate-associated lineages.

Diversity and salinity adaptations of ammonia oxidizing archaea in three estuaries of China

Ammonia-oxidizing archaea (AOA) are ubiquitously found in diverse habitats and play pivotal roles in the nitrogen and carbon cycle, especially in estuarine and coastal environments. Despite the fact that the diversity and distribution of AOA are thought to be tightly linked to habitats, little is known about the relationship that underpins their genomic traits, adaptive potentials, and ecological niches. Here, we have characterized and compared the AOA community in three estuaries of China using metagenomics. AOA were the dominant ammonia oxidizers in the three estuaries. Through phylogenetic analyses, five major AOA groups were identified, including the Nitrosomarinus-like, Nitrosopumilus-like, Aestuariumsis-like, Nitrosarchaeum-like, and Nitrosopelagicus-like groups. Statistical analyses showed that the aquatic and sedimentary AOA communities were mainly influenced by spatial factors (latitude and water depth) and environmental factors (salinity, pH, and dissolved oxygen) in estuaries, respectively. Compared to AOA dwelling in terrestrial and marine habitats, estuarine AOA encoded more genes involved in glucose and amino acid metabolism, transport systems, osmotic control, and cell motility. The low proteome isoelectric points (pI), high content of acidic amino acids, and the presence of potassium ion and mechanosensitive channels suggest a "salt-in" strategy for estuarine AOA to counteract high osmolarity in their surroundings. Our findings have indicated potential adaptation strategies and highlighted their importance in the estuarine nitrogen and carbon cycles. KEY POINTS: • Spatial and environmental factors influence water and sediment AOA respectively. • Estuarine AOA share low proteome isoelectric value and high acid amino acids content. • AOA adaptation to estuaries is likely resulted from their unique genomic features.

Changing microbiome community structure and functional potential during permafrost thawing on the Tibetan Plateau

Large amounts of carbon sequestered in permafrost on the Tibetan Plateau (TP) are becoming vulnerable to microbial decomposition in a warming world. However, knowledge about how the responsible microbial community responds to warming-induced permafrost thaw on the TP is still limited. This study aimed to conduct a comprehensive comparison of the microbial communities and their functional potential in the active layer of thawing permafrost on the TP. We found that the microbial communities were diverse and varied across soil profiles. The microbial diversity declined and the relative abundance of Chloroflexi, Bacteroidetes, Euryarchaeota, and Bathyarchaeota significantly increased with permafrost thawing. Moreover, warming reduced the similarity and stability of active layer microbial communities. The high-throughput qPCR results showed that the abundance of functional genes involved in liable carbon degradation and methanogenesis increased with permafrost thawing. Notably, the significantly increased mcrA gene abundance and the higher methanogens to methanotrophs ratio implied enhanced methanogenic activities during permafrost thawing. Overall, the composition and functional potentials of the active layer microbial community in the Tibetan permafrost region are susceptible to warming. These changes in the responsible microbial community may accelerate carbon degradation, particularly in the methane releases from alpine permafrost ecosystems on the TP.

Extreme summers impact cropland and grassland soil microbiomes

The increasing frequency of extreme weather events highlights the need to understand how soil microbiomes respond to such disturbances. Here, metagenomics was used to investigate the effects of future climate scenarios (+0.6 °C warming and altered precipitation) on soil microbiomes during the summers of 2014-2019. Unexpectedly, Central Europe experienced extreme heatwaves and droughts during 2018-2019, causing significant impacts on the structure, assembly, and function of soil microbiomes. Specifically, the relative abundance of Actinobacteria (bacteria), Eurotiales (fungi), and Vilmaviridae (viruses) was significantly increased in both cropland and grassland. The contribution of homogeneous selection to bacterial community assembly increased significantly from 40.0% in normal summers to 51.9% in extreme summers. Moreover, genes associated with microbial antioxidant (Ni-SOD), cell wall biosynthesis (glmSMU, murABCDEF), heat shock proteins (GroES/GroEL, Hsp40), and sporulation (spoIID, spoVK) were identified as potential contributors to drought-enriched taxa, and their expressions were confirmed by metatranscriptomics in 2022. The impact of extreme summers was further evident in the taxonomic profiles of 721 recovered metagenome-assembled genomes (MAGs). Annotation of contigs and MAGs suggested that Actinobacteria may have a competitive advantage in extreme summers due to the biosynthesis of geosmin and 2-methylisoborneol. Future climate scenarios caused a similar pattern of changes in microbial communities as extreme summers, but to a much lesser extent. Soil microbiomes in grassland showed greater resilience to climate change than those in cropland. Overall, this study provides a comprehensive framework for understanding the response of soil microbiomes to extreme summers.

A glimpse of the paleome in endolithic microbial communities

BACKGROUND

The terrestrial subsurface is home to a significant proportion of the Earth's microbial biomass. Our understanding about terrestrial subsurface microbiomes is almost exclusively derived from groundwater and porous sediments mainly by using 16S rRNA gene surveys. To obtain more insights about biomass of consolidated rocks and the metabolic status of endolithic microbiomes, we investigated interbedded limestone and mudstone from the vadose zone, fractured aquifers, and deep aquitards.

RESULTS

By adapting methods from microbial archaeology and paleogenomics, we could recover sufficient DNA for downstream metagenomic analysis from seven rock specimens independent of porosity, lithology, and depth. Based on the extracted DNA, we estimated between 2.81 and 4.25 × 105 cells × g-1 rock. Analyzing DNA damage patterns revealed paleome signatures (genetic records of past microbial communities) for three rock specimens, all obtained from the vadose zone. DNA obtained from deep aquitards isolated from surface input was not affected by DNA decay indicating that water saturation and not flow is controlling subsurface microbial survival. Decoding the taxonomy and functional potential of paleome communities revealed increased abundances for sequences affiliated with chemolithoautotrophs and taxa such as Cand. Rokubacteria. We also found a broader metabolic potential in terms of aromatic hydrocarbon breakdown, suggesting a preferred utilization of sedimentary organic matter in the past.

CONCLUSIONS

Our study suggests that limestones function as archives for genetic records of past microbial communities including those sensitive to environmental stress at modern times, due to their specific conditions facilitating long-term DNA preservation. Video Abstract.

Nitrification and beyond: metabolic versatility of ammonia oxidising archaea

Ammonia oxidising archaea are among the most abundant living organisms on Earth and key microbial players in the global nitrogen cycle. They carry out oxidation of ammonia to nitrite, and their activity is relevant for both food security and climate change. Since their discovery nearly 20 years ago, major insights have been gained into their nitrogen and carbon metabolism, growth preferences and their mechanisms of adaptation to the environment, as well as their diversity, abundance and activity in the environment. Despite significant strides forward through the cultivation of novel organisms and omics-based approaches, there are still many knowledge gaps on their metabolism and the mechanisms which enable them to adapt to the environment. Ammonia oxidising microorganisms are typically considered metabolically streamlined and highly specialised. Here we review the physiology of ammonia oxidising archaea, with focus on aspects of metabolic versatility and regulation, and discuss these traits in the context of nitrifier ecology.

Short- and long-term effects of continuous compost amendment on soil microbiome community

Organic amendment, and especially the use of composts, is a well-accepted sustainable agricultural practice. Compost increases soil carbon and microbial biomass, changes enzymatic activity, and enriches soil carbon and nitrogen stocks. However, relatively little is known about the immediate and long-term temporal dynamics of agricultural soil microbial communities following repeated compost applications. Our study was conducted at two field sites: Newe Ya'ar (NY, Mediterranean climate) and Gilat (G, semi-arid climate), both managed organically over 4 years under either conventional fertilization (0, zero compost) or three levels of compost amendment (20, 40 and 60 m3/ha or 2, 4, 6 L/m2). Microbial community dynamics in the soils was examined by high- and low-time-resolution analyses. Annual community composition in compost-amended soils was significantly affected by compost amendment levels in G (first, second and third years) and in NY (third year). Repeated sampling at high resolution (9-10 times over 1 year) showed that at both sites, compost application initially induced a strong shift in microbial communities, lasting for up to 1 month, followed by a milder response. Compost application significantly elevated alpha diversity at both sites, but differed in the compost-dose correlation effect. We demonstrate higher abundance of taxa putatively involved in organic decomposition and characterized compost-related indicator taxa and a compost-derived core microbiome at both sites. Overall, this study describes temporal changes in the ecology of soil microbiomes in response to compost vs. conventional fertilization.

Detrimental effects of Cd and temperature on rice and functions of microbial community in paddy soils

Heavy metal (HM) contamination and high environmental temperature (HT) are caused by anthropogenic activities that negatively impact soil microbial communities and agricultural productivity. Although HM contaminations have deleterious effects on microbes and plants; there are hardly any reports on the combined effects of HM and HT. Here, we reported that HT coupled with cadmium (Cd) accumulation in soil and irrigated water could seriously affect crop growth and productivity, alternatively influencing the microbial community and nutrient cycles of paddy soils in rice fields. We analyzed different mechanisms of plants and microflora in the rhizospheric region, such as plant rhizospheric nitrification, endophytes colonization, nutrient uptake, and physiology of temperature-sensitive (IR64) and temperature-resistant Huanghuazhan (HZ) rice cultivars against different Cd levels (2, 5 and 10 mg kg^-1) with rice plants grown under 25 °C and 40 °C temperatures. Consequently, an increment in Cd accumulation was observed with rising temperature leading to enhanced expression of OsNTRs. In contrast, a greater decline in the microbial community was detected in IR64 cultivar than HZ. Similarly, ammonium oxidation, root-IAA, shoot-ABA production, and 16S rRNA gene abundance in the rhizosphere and endosphere were significantly influenced by HT and Cd levels, resulting in a significant decrease in the colonization of endophytes and the surface area of roots, leading to a decreased N uptake from the soil. Overall, the outcomes of this study unveiled the novel effects of Cd, temperature, and their combined effect on rice growth and functions of the microbial community. These results provide effective strategies to overcome Cd-phytotoxicity on the health of endophytes and rhizospheric bacteria in Cd-contaminated soil by using temperature-tolerant rice cultivars.

Sensitive or tolerant functional microorganisms under cadmium stress: suggesting potential specific interaction network characteristics in the rhizosphere system of karst potato

The heavy metal cadmium (Cd) pollution in Chinese karst soils threatens food security, and microorganisms play an important role in regulating the migration and transformation of Cd in the soil-plant system. Nevertheless, the interaction characteristics between key microbial communities and environmental factors in response to Cd stress in specific crop environmental systems need to be explored. In this study, the soil (ferralsols)-microbe-crop (potato) system was taken as the object to explore the potato rhizosphere microbiome, using toxicology and molecular biology approaches, to explore the potato rhizosphere soil properties, microbial stress characteristics, and important microbial taxa under Cd stress. We hypothesized that different members of fungal and bacterial microbiome would regulate the resilience of potato rhizosphere and plants to Cd stress in the soil environment. Meanwhile, individual taxa will have different roles in the contaminated rhizosphere ecosystem. We found that soil pH was the main environmental factor affecting fungal community structure; urea-decomposing and nitrate-reducing functional bacteria as well as endosymbiotic and saprophytic functional fungi gradually decreased. In particular, Basidiomycota may play a key role in preventing the migration of Cd from the soil to plants (potato). These findings provide important candidates for screening the cascade of Cd inhibition (detoxification/regulation) from soil to microorganisms to plants. Our work provides an important foundation and research insights for the application of microbial remediation technology in the karst cadmium-contaminated farmland.

Ether lipids from archaeas in nano-drug delivery and vaccination

Archaea are microorganisms more closely related to eukaryotes than bacteria. Almost 50 years after being defined as a new domain of life on earth, new species continue to be discovered and their phylogeny organized. The study of the relationship between their genetics and metabolism and some of their extreme habitats has even positioned them as a model of extraterrestrial life forms. Archaea, however, are deeply connected to the life of our planet: they can be found in arid, acidic, warm areas; on most of the earth's surface, which is cold (below 5 °C), playing a prominent role in the cycles of organic materials on a global scale and they are even part of our microbiota. The constituent materials of these microorganisms differ radically from those produced by eukaryotes and bacteria, and the nanoparticles that can be manufactured using their ether lipids as building blocks exhibit unique properties that are of interest in nanomedicine. Here, we present for the first time a complete overview of the pre-clinical applications of nanomedicines based on ether archaea lipids, focused on drug delivery and adjuvancy over the last 25 years, along with a discussion on their pros, cons and their future industrial implementation.

Adaptive genetic traits in pelagic freshwater microbes

Pelagic microbes have adopted distinct strategies to inhabit the pelagial of lakes and oceans and can be broadly categorized in two groups: free-living, specialized oligotrophs and patch-associated generalists or copiotrophs. In this review, we aim to identify genomic traits that enable pelagic freshwater microbes to thrive in their habitat. To do so, we discuss the main genetic differences of pelagic marine and freshwater microbes that are both dominated by specialized oligotrophs and the difference to freshwater sediment microbes, where copiotrophs are more prevalent. We phylogenomically analysed a collection of >7700 metagenome-assembled genomes, classified habitat preferences on different taxonomic levels, and compared the metabolic traits of pelagic freshwater, marine, and freshwater sediment microbes. Metabolic differences are mainly associated with transport functions, environmental information processing, components of the electron transport chain, osmoregulation and the isoelectric point of proteins. Several lineages with known habitat transitions (Nitrososphaeria, SAR11, Methylophilaceae, Synechococcales, Flavobacteriaceae, Planctomycetota) and the underlying mechanisms in this process are discussed in this review. Additionally, the distribution, ecology and genomic make-up of the most abundant freshwater prokaryotes are described in details in separate chapters for Actinobacteriota, Bacteroidota, Burkholderiales, Verrucomicrobiota, Chloroflexota, and 'Ca. Patescibacteria'.

Using thermodynamics to obtain geochemical information from genomes

Thermodynamic characterization of the relative stabilities of chemical compounds is a pillar of conceptual models in various fields of geosciences. Analogous models applied to genomes can yield new information about the relationship between genomes and their geochemical environments. In this perspective article, we present a chemical and thermodynamic analysis of prokaryotic lineages that have been the target of previous phylogenomic studies of evolutionary adaptation to varying redox conditions. The thermodynamic model development begins by quantifying the effects of hydrogen activity (aH₂ ) and temperature on the relative stabilities of organic compounds with different carbon oxidation state. When applied to proteins instead of metabolites, the same techniques can be used to identify combinations of aH₂ and temperature at which reference proteomes for Class I or Class II methanogens are relatively stable. The calculated aH₂ values are compatible with reported measurements for habitats of methanogens ranging from highly reducing submarine hydrothermal systems to less reducing environments including methanogenic sediments. In contrast to the transition between the two classes of methanogenic archaea, that between basal and terrestrial groups of Thaumarchaeota (denoting the origin of ammonia-oxidizing archaea) occurs at a less-reducing redox boundary. These examples reveal the consequences of energy minimization driving evolution and show how geochemical calculations involving biomolecules can be used to quantify and better understand the coevolution of the geosphere and biosphere.

The Predominance of Ammonia-Oxidizing Archaea in an Oceanic Microbial Community Amended with Cyanobacterial Lysate

When the oligotrophic microbial community was amended with Synechococcus-derived dissolved organic matter (SDOM) and incubated under the dark condition, archaea relative abundance was initially very low but made up more than 60% of the prokaryotic community on day 60, and remained dominant for at least 9 months. The archaeal sequences were dominated by Candidatus Nitrosopumilus, the Group I.1a Thaumarchaeota. The increase of Thaumarchaeota in the dark incubation corresponded to the period of delayed ammonium oxidation upon an initially steady increase in ammonia, supporting the remarkable competency of Thaumarchaeota in energy utilization and fixation of inorganic carbon in the ocean. IMPORTANCE Thaumarchaeota, which are ammonia-oxidizing archaea (AOA), are mainly chemolithoautotrophs that can fix inorganic carbon to produce organic matter in the dark. Their distinctive physiological traits and high abundance in the water column indicate the significant ecological roles they play in the open ocean. In our study, we found predominant Thaumarchaeota in the microbial community amended with cyanobacteria-derived lysate under the dark condition. Furthermore, Thaumarchaeota remained dominant in the microbial community even after 1 year of incubation. Through the ammonification process, dissolved organic matter (DOM) from cyanobacterial lysate was converted to ammonium which was used as an energy source for Thaumarchaeota to fix inorganic carbon into biomass. Our study further advocates the important roles of Thaumarchaeota in the ocean's biogeochemical cycle.

Uncovering the Microbial Diversity of Two Exotic Calcareous Sponges

Sponges-associated microorganisms play important roles in their health and ecology; consequently, they may be crucial in the successful adaptation of exotic species to novel environments. However, few studies have focused on the microbial diversity of exotic sponges, especially those with calcium carbonate spicules (class Calcarea). Therefore, this is the first in situ characterization of the microbiota of the exotic calcareous sponges Sycettusa hastifera and Paraleucilla magna. Our results suggest that S. hastifera has a more stable microbiota than P. magna, as there were no differences in its beta diversity among sampling sites. Conversely, P. magna showed significant differences in its microbial communities, perhaps related to its adhesion to artificial substrate and/or shellfish mariculture activities. Each sponge species presented a single dominant proteobacterial OTU potentially active in the nitrogen cycle, which could help sponge detoxification, especially in polluted areas where exotic species usually establish. Our results show the importance of assessing the microbial diversity to unveil host-microorganism relationships and suggest that these associated nitrogen-cycling microorganisms could favor the success of exotic sponges in new environments.

Diverse Bathyarchaeotal Lineages Dominate Archaeal Communities in the Acidic Dajiuhu Peatland, Central China

Bathyarchaeota are believed to have roles in the carbon cycle in marine systems. However, the ecological knowledge of Bathyarchaeota is limited in peatland ecosystems. Here, we investigated the vertical distribution of Bathyarchaeota community structure using quantitative PCR and high-throughput sequencing technology of ribosomal 16S rRNA gene integrated with detailed chemical profiling in the Dajiuhu Peatland, central China. Eight archaeal phyla were observed in peat samples, which mainly composed of Bathyarchaeota with a mean relative abundance about 88%, followed by Thaumarchaeota (9%). Bathyarchaeota were further split into 17 subgroups, and some subgroups showed habitat specificity to peat horizons with distinct lithological and physicochemical properties, for example, Bathy-6 and Bathy-15 had preference for the acrotelm, Bathy-5b, Bathy-16, and Bathy-19 were enriched in the catotelm, Bathy-5a, Bathy-8, and Bathy-11 were specific for the clay horizon. This spatial distribution pattern of archaeal communities along peat profile was mainly influenced by water content as indicated by RDA ordination and permutational MANOVA, whereas organic matter content exclusively affected Bathyarchaeota distribution along the peat profile significantly. The abundance of archaeal 16S rRNA genes ranged from 10⁵ to 10⁷ copies per gram dry sediment, and the highest archaeal biomass was observed in the periodically oxic mesotelm horizon with more dynamic archaeal interaction relationship as indicated by the network analysis. Bathyarchaeota dominated the archaeal interaction network with 82% nodes, 96% edges, and 71% keystone species. Our results provide an overview of the archaeal population, community structure, and relationship with environmental factors that affect the vertical distribution of archaeal communities and emphasize the ecology of bathyarchaeotal lineages in terrestrial peatland ecosystems.

Microbial diversity across compartments in an aquaponic system and its connection to the nitrogen cycle

Aquaponics combines hydroponic crop production with recirculating aquaculture. These systems comprise various compartments (fish tank, biofilter, sump, hydroponic table, radial flow settler and anaerobic digester), each with their own specific environmental pressures, which trigger the formation of unique microbial communities. Triplicated aquaponic systems were used to investigate the microbial community composition during three lettuce growing cycles. The sampling of individual compartments allowed community patterns to be generated using amplicon sequencing of bacterial and archaeal 16S rRNA genes. Nitrifying bacteria were identified in the hydroponic compartments, indicating that these compartments may play a larger role than previously thought in the system's nitrogen cycle. In addition to the observed temporal changes in community compositions within the anaerobic compartment, more archaeal reads were obtained from sludge samples than from the aerobic part of the system. Lower bacterial diversity was observed in fresh fish feces, where a highly discrete gut flora composition was seen. Finally, the most pronounced differences in microbial community compositions were observed between the aerobic and anaerobic loops of the system, with unique bacterial compositions in each individual compartment.

Elevational changes in the bacterial community composition and potential functions in a Tibetan grassland

In the Tibetan grasslands, the distribution patterns of the microbial community structure and function along elevation gradients have attracted considerable attention due to the wide distribution of mountain slopes, but the controlling factors of these patterns are still unclear. Here we investigated the taxonomy and potential functions of soil bacteria along an elevation gradient in a Tibetan mountainous grassland in 2 years, aiming to explore the elevation patterns of the bacterial structure and function and the underlying drivers. High-throughput sequencing and environment attribute measurements were conducted to survey the bacterial and environment characters. Furthermore, PICRUSt2 for prediction of bacterial functions, iCAMP for unraveling the drivers controlling community assembly, and HMSC for variance partitioning of bacterial community composition were used. Elevation did not significantly affect the bacterial diversity but changed their composition, driven by both deterministic and stochastic processes. In addition, elevation did not significantly affect the relative importance of deterministic and stochastic processes. Soil carbon, nitrogen, and temperature were important deterministic factors in driving bacterial community structure. The genus Solirubrobacter in Actinobacteriota was identified as most elevation discriminatory. Based on these observations, the bacterial community in the Tibetan mountainous grasslands was more controlled by edaphic factors than temperature, indicating their relative stability under climate change scenarios.

Conserved and lineage-specific hypothetical proteins may have played a central role in the rise and diversification of major archaeal groups

BACKGROUND

Archaea play fundamental roles in the environment, for example by methane production and consumption, ammonia oxidation, protein degradation, carbon compound turnover, and sulfur compound transformations. Recent genomic analyses have profoundly reshaped our understanding of the distribution and functionalities of Archaea and their roles in eukaryotic evolution.

RESULTS

Here, 1179 representative genomes were selected from 3197 archaeal genomes. The representative genomes clustered based on the content of 10,866 newly defined archaeal protein families (that will serve as a community resource) recapitulates archaeal phylogeny. We identified the co-occurring proteins that distinguish the major lineages. Those with metabolic roles were consistent with experimental data. However, two families specific to Asgard were determined to be new eukaryotic signature proteins. Overall, the blocks of lineage-specific families are dominated by proteins that lack functional predictions.

CONCLUSIONS

Given that these hypothetical proteins are near ubiquitous within major archaeal groups, we propose that they were important in the origin of most of the major archaeal lineages. Interestingly, although there were clearly phylum-specific co-occurring proteins, no such blocks of protein families were shared across superphyla, suggesting a burst-like origin of new lineages early in archaeal evolution.

Candidatus Nitrosopolaris, a genus of putative ammonia-oxidizing archaea with a polar/alpine distribution

Ammonia-oxidizing archaea (AOA) are key players in the nitrogen cycle of polar soils. Here, we analyzed metagenomic data from tundra soils in Rásttigáisá, Norway, and recovered four metagenome-assembled genomes (MAGs) assigned to the genus 'UBA10452', an uncultured lineage of putative AOA in the order Nitrososphaerales ('terrestrial group I.1b'), phylum Thaumarchaeota. Analysis of other eight previously reported MAGs and publicly available amplicon sequencing data revealed that the UBA10452 lineage is predominantly found in acidic polar and alpine soils. In particular, UBA10452 MAGs were more abundant in highly oligotrophic environments such as mineral permafrost than in more nutrient-rich, vegetated tundra soils. UBA10452 MAGs harbour multiple copies of genes related to cold tolerance, particularly genes involved in DNA replication and repair. Based on the phylogenetic, biogeographic, and ecological characteristics of 12 UBA10452 MAGs, which include a high-quality MAG (90.8% complete, 3.9% redundant) with a nearly complete 16S rRNA gene, we propose a novel Candidatus genus, Ca. Nitrosopolaris, with four species representing clear biogeographic/habitat clusters.

Distribution of ammonia oxidizers and their role in N2 O emissions in the reservoir riparian zone

As a transitional boundary between terrestrial and aquatic ecosystems, the riparian zone is considered a hotspot for N₂ O production because of the active nitrogen processes. Ammoxidation is an important microbial pathway for N₂ O production, but the distribution of ammonia oxidizers under different land-use types in the reservoir riparian zone and what role they played in N₂ O emissions are still not clear. We investigated spatiotemporal distributions of ammonia-oxidizing archaea (AOA) and bacteria (AOB) and their role in N₂ O emissions in different land-use types along the riparian zone of Miyun Reservoir: grassland, sparse woods, and woodland. We found significant differences in both AOA abundance and AOB diversity indices among land-use types. AOA and AOB communities were significantly separated by different land-use types. The main drivers to determine the distribution of ammonia-oxidizing microbial community were soil water content, NH₄ ⁺ , NO₃ ^- , and total organic carbon (TOC). In situ N₂ O flux was highest in woodland with a mean value of 12.28 μg/m² ·h, and it was substantially decreased by 121% and 123% in sparse woods and grassland. TOC content was decreased by 20% and 40% in sparse woods and grassland compared with woodland, and it was significantly positively correlated with in situ N₂ O flux. Meanwhile, AOB diversity indices were significantly correlated with in situ N₂ O flux. These results showed that the heterogeneity of physicochemical properties among different land-use types affected the community of AOA and AOB in riparian zones. AOB not AOA, and community diversity rather than abundance, played a role in N₂ O emissions.

All Set before Flowering: A 16S Gene Amplicon-Based Analysis of the Root Microbiome Recruited by Common Bean (Phaseolus vulgaris) in Its Centre of Domestication

Plant roots recruit most prokaryotic members of their root microbiota from the locally available inoculum, but knowledge on the contribution of native microorganisms to the root microbiota of crops in native versus non-native areas remains scarce. We grew common bean (Phaseolus vulgaris) at a field site in its centre of domestication to characterise rhizosphere and endosphere bacterial communities at the vegetative, flowering, and pod filling stage. 16S r RNA gene amplicon sequencing of ten samples yielded 9,401,757 reads, of which 8,344,070 were assigned to 17,352 operational taxonomic units (OTUs). Rhizosphere communities were four times more diverse than in the endosphere and dominated by Actinobacteria, Bacteroidetes, Crenarchaeota, and Proteobacteria (endosphere: 99% Proteobacteria). We also detected high abundances of Gemmatimonadetes (6%), Chloroflexi (4%), and the archaeal phylum Thaumarchaeota (Candidatus Nitrososphaera: 11.5%): taxa less frequently reported from common bean rhizosphere. Among 154 OTUs with different abundances between vegetative and flowering stage, we detected increased read numbers of Chryseobacterium in the endosphere and a 40-fold increase in the abundances of OTUs classified as Rhizobium and Aeromonas (equivalent to 1.5% and over 6% of all reads in the rhizosphere). Our results indicate that bean recruits specific taxa into its microbiome when growing 'at home'.

Continental-scale niche differentiation of dominant topsoil archaea in drylands

Archaea represent a diverse group of microorganisms often associated with extreme environments. However, an integrated understanding of biogeographical patterns of the specialist Haloarchaea and the potential generalist ammonia-oxidizing archaea (AOA) across large-scale environmental gradients remains limited. We hypothesize that niche differentiation determines their distinct distributions along environmental gradients. To test the hypothesis, we use a continental-scale research network including 173 dryland sites across northern China. Our results demonstrate that Haloarchaea and AOA dominate topsoil archaeal communities. As hypothesized, Haloarchaea and AOA show strong niche differentiation associated with two ecosystem types mainly found in China's drylands (i.e., deserts vs. grasslands), and they differ in the degree of habitat specialization. The relative abundance and richness of Haloarchaea are higher in deserts due to specialization to relatively high soil salinity and extreme climates, while those of AOA are greater in grassland soils. Our results further indicate a divergence in ecological processes underlying the segregated distributions of Haloarchaea and AOA. Haloarchaea are governed primarily by environmental-based processes while the more generalist AOA are assembled mostly via spatial-based processes. Our findings add to existing knowledge of large-scale biogeography of topsoil archaea, advancing our predictive understanding on changes in topsoil archaeal communities in a drier world. This article is protected by copyright. All rights reserved.

Factors shaping the abundance and diversity of the gut archaeome across the animal kingdom

Archaea are common constituents of the gut microbiome of humans, ruminants, and termites but little is known about their diversity and abundance in other animals. Here, we analyse sequencing and quantification data of archaeal and bacterial 16S rRNA genes from 250 species of animals covering a large taxonomic spectrum. We detect the presence of archaea in 175 animal species belonging to invertebrates, fish, amphibians, birds, reptiles and mammals. We identify five dominant gut lineages, corresponding to Methanobrevibacter, Methanosphaera, Methanocorpusculum, Methanimicrococcus and "Ca. Methanomethylophilaceae". Some archaeal clades, notably within Methanobrevibacter, are associated to certain hosts, suggesting specific adaptations. The non-methanogenic lineage Nitrososphaeraceae (Thaumarchaeota) is frequently present in animal samples, although at low abundance, but may have also adapted to the gut environment. Host phylogeny, diet type, fibre content, and intestinal tract physiology are major drivers of the diversity and abundance of the archaeome in mammals. The overall abundance of archaea is more influenced by these factors than that of bacteria. Methanogens reducing methyl-compounds with H₂ can represent an important fraction of the overall methanogens in many animals. Together with CO₂-reducing methanogens, they are influenced by diet and composition of gut bacteria. Our results provide key elements toward our understanding of the ecology of archaea in the gut, an emerging and important field of investigation.

Phylogenomic Analysis of Metagenome-Assembled Genomes Deciphered Novel Acetogenic Nitrogen-Fixing Bathyarchaeota from Hot Spring Sediments

This study describes the phylogenomic analysis and metabolic insights of metagenome-assembled genomes (MAGs) retrieved from hot spring sediment samples. The metagenome-assembled sequences recovered three near-complete genomes belonging to the archaeal phylum. Analysis of genome-wide core genes and 16S rRNA-based phylogeny placed the ILS200 and ILS300 genomes within the uncultivated and largely understudied bathyarchaeal phylum, whereas ILS100 represented the phylum Thaumarchaeota. The average nucleotide identity (ANI) of the bin ILS100 was 76% with Nitrososphaeria_archaeon_isolate_SpSt-1069. However, the bins ILS200 and ILS300 showed ANI values of 75% and 70% with Candidatus_Bathyarchaeota_archaeon_isolate_DRTY-6_2_bin_115 and Candidatus_Bathyarchaeota_archaeon_BA1_ba1_01, respectively. The genomic potential of Bathyarchaeota bins ILS200 and ILS300 showed genes necessary for the Wood-Ljungdahl pathway, and the gene encoding the methyl coenzyme M reductase (mcr) complex essential for methanogenesis was absent. The metabolic potential of the assembled genomes included genes involved in nitrogen assimilation, including nitrogenase and the genes necessary for the urea cycle. The presence of these genes suggested the metabolic potential of Bathyarchaeota to fix nitrogen under extreme environments. In addition, the ILS200 and ILS300 genomes carried genes involved in the tricarboxylic acid (TCA) cycle, glycolysis, and degradation of organic carbons. Finally, we conclude that the reconstructed Bathyarchaeota bins are autotrophic acetogens and organo-heterotrophs.

IMPORTANCE We describe the Bathyarchaeota bins that are likely to be acetogens with a wide range of metabolic potential. These bins did not exhibit methanogenic machinery, suggesting methane production may not occur by all subgroup lineages of Bathyarchaeota. Phylogenetic analysis support that both ILS200 and ILS300 belonged to the Bathyarchaeota. The discovery of new bathyarchaeotal MAGs provides additional knowledge for understanding global carbon and nitrogen metabolism under extreme conditions.

Microbial diversity and community structure in deep-sea sediments of South Indian Ocean

Microbial communities composed of bacteria, archaea and fungi play a pivotal role in driving the biogeochemical cycles in the marine ecosystem. Despite the vastness of the South Indian Ocean, only a few studies reported the simultaneous analysis of bacterial, archaeal and fungal diversity therein, particularly archaeal and fungal communities in deep-sea environments received less attention previously. In this study, microbial diversity, community composition and dynamics in microbial community structure in eight deep-sea sediment samples collected from different sites at varying depths of the South Indian Ocean were explored using Next-Generation Sequencing. In total, 21 bacterial phyla representing 541 OTUs were identified from the eight samples, where phylum Proteobacteria was found as the most abundant bacterial phylum in five out of eight samples. Firmicutes and Chloroflexi were the dominant phyla in the rest of the three samples. In the case of archaea, uncultured species belonging to the phyla Thaumarchaeota and Euryarchaeota were the abundant taxa in all the samples. Similarly, Ascomycota and Basidiomycota were the most abundant fungal phyla present therein. In all the eight samples studied here, about 10-58% and 19-26% OTUs in archaeal and fungal communities were mapped to unclassified taxa respectively, suggesting the lack of representation in databases. Co-occurrence network analysis further revealed that bacterial communities tend to be more dynamic than archaeal and fungal communities. This study provides interesting insights into the microbial diversity, community composition and dynamics in microbial community structure in the deep-sea sediments of the South Indian Ocean.

Unique Geothermal Chemistry Shapes Microbial Communities on Mt. Erebus, Antarctica

Mt. Erebus, Antarctica, is the world's southernmost active volcano and is unique in its isolation from other major active volcanic systems and its distinctive geothermal systems. Using 16S rRNA gene amplicon sequencing and physicochemical analyses, we compared samples collected at two contrasting high-temperature (50°C-65°C) sites on Mt. Erebus: Tramway Ridge, a weather-protected high biomass site, and Western Crater, an extremely exposed low biomass site. Samples were collected along three thermal gradients, one from Western Crater and two within Tramway Ridge, which allowed an examination of the heterogeneity present at Tramway Ridge. We found distinct soil compositions between the two sites, and to a lesser extent within Tramway Ridge, correlated with disparate microbial communities. Notably, pH, not temperature, showed the strongest correlation with these differences. The abundance profiles of several microbial groups were different between the two sites; class Nitrososphaeria amplicon sequence variants (ASVs) dominated the community profiles at Tramway Ridge, whereas Acidobacteriotal ASVs were only found at Western Crater. A co-occurrence network, paired with physicochemical analyses, allowed for finer scale analysis of parameters correlated with differential abundance profiles, with various parameters (total carbon, total nitrogen, soil moisture, soil conductivity, sulfur, phosphorous, and iron) showing significant correlations. ASVs assigned to Chloroflexi classes Ktedonobacteria and Chloroflexia were detected at both sites. Based on the known metabolic capabilities of previously studied members of these groups, we predict that chemolithotrophy is a common strategy in this system. These analyses highlight the importance of conducting broader-scale metagenomics and cultivation efforts at Mt. Erebus to better understand this unique environment.

Microbial community structure and metabolic potential in the coastal sediments around the Yellow River Estuary

The Yellow River Estuary and Laizhou Bay are located on the northern Shandong Peninsula in the Bohai Sea in China and have been polluted by intensive anthropogenic activity. However, few studies have focused on the effect of these activities on the microbial communities and their ecological functions in this area. In this study, the combination of 16S rDNA gene sequencing and GeoChip technology was used to analyzed the microbial community component and their functional genes. Thaumarchaeot and Bacteroidetes are the most abundant phyla. The results of correlation analysis and redundancy analysis (RDA) showed water depth (r² = 0.76, P = 0.005), total Na content (r² = 0.63, P = 0.021) and total Ca content (r² = 0.53, P = 0.05) in the sediments were the most significant environmental factors affecting the microbial community. The diversity of the microbial community and signal intensity of functional genes at nearshore sites (N sites) were higher than that at the offshore sites (O sites), but the component of microbial community and functional genes was similar in general. Functional genes for C, N, P and S cycle were detected at both nearshore and offshore sites, which illustrated that microbial communities were active in nutrient cycle. Proteobacteria contributes significantly to material cycle in microbial community. In addition, functional genes related to organic remediation and metal detoxification are also abundant. It indicated that the environmental pollution caused by anthropogenic activities has greatly affected the microbial community components and their biochemical functions in the Yellow River Estuary and surrounding areas. This study reveals the effect of anthropogenic activities on microbial communities and provides the basis for environmental management.

From Rags to Enriched: Metagenomic Insights into Ammonia-oxidizing Archaea Following Ammonia Enrichment of a Denuded Oligotrophic Soil Ecosystem

Stored topsoil acts as a microbial inoculant for ecological restoration of land after disturbance, but the altered circumstances frequently create unfavorable conditions for microbial survival. Nitrogen cycling is a critical indicator for ecological success and this study aimed to investigate the cornerstone taxa driving the process. Previous in-silico studies investigating stored topsoil discovered persistent archaeal taxa with the potential for re-establishing ecological activity. Ammonia oxidization is the limiting step in nitrification and as such, ammonia oxidizing archaea (AOA) can be considered as the one of the gatekeepers for the re-establishment of the nitrogen cycle in disturbed soils. Semi-arid soil samples were enriched with ammonium sulfate to promote the selective enrichment of ammonia oxidizers for targeted genomic recovery, and to investigate the microbial response of the microcosm to nitrogen input. Ammonia addition produced an increase in AOA population, particularly within the genus Candidatus Nitrosotalea, from which metagenome-assembled genomes (MAGs) were successfully recovered. The Ca. Nitrosotalea archaeon candidates' ability to survive in extreme conditions and rapidly respond to ammonia input makes it a potential bioprospecting target for application in ecological restoration of semi-arid soils and the recovered MAGs provide a metabolic blueprint for developing potential strategies towards isolation of these acclimated candidates. This article is protected by copyright. All rights reserved.

Biodiversity and Biogeography of Abundant and Rare Microbial Assemblages in the Western Subtropical Pacific Ocean

The levels of chlorophyll a and nutrient concentrations in the surface waters of the western subtropical Pacific Ocean are among the lowest globally. In addition, our knowledge of basin-scale diversity and biogeography of microbial communities in this vast extremely oligotrophic environment is still rather limited. Here, high-throughput sequencing was used to examine the biodiversity and biogeography of abundant and rare microbial assemblages throughout the water column from the surface to a depth of 3,000 m across a horizontal distance of 1,100 km in the western Pacific Ocean. Microbial alpha diversity in the 200-m layer was higher than at other depths, with Gammaproteobacteria, Alphaproteobacteria, and Clostridia as the dominant classes in all samples. Distinctly vertical distributions within the microbial communities were revealed, with no difference horizontally. Some microbes exhibited depth stratification. For example, the relative abundances of Cyanobacteria and Alphaproteobacteria decreased with depth, while Nitrososphaeria, Actinobacteria, and Gammaproteobacteria increased with depth in the aphotic layers. Furthermore, we found that environmental (selective process) and spatial (neutral process) factors had different effects on abundant and rare taxa. Geographical distance showed little effect on the dispersal of all and abundant taxa, while statistically significant distance-decay relationships were observed among the rare taxa. Temperature and chlorophyll a were strongly associated with all, abundant, and rare taxa in the photic layers, while total inorganic nitrogen was recognized as the crucial factor in the aphotic layers. Variance partitioning analysis indicated that environmental selection played a relatively important role in shaping all and abundant taxa, while the variation in rare taxa explained by environmental and spatial processes was relatively low, as more than 70% of the variation remained unexplained. This study provides novel knowledge related to microbial community diversity in the western subtropical Pacific Ocean, and the analyzes biogeographical patterns among abundant and rare taxa.

Metagenomics: A New Direction in Ecology

Abstract

The prospects for application of metagenomic technologies in environmental studies are discussed. The advantages in investigating the taxonomic composition of aquatic and terrestrial ecosystems, as well as examples of trophic and phoric relationships found in ecosystems using the metagenomic approach, are described. The capabilities of metagenomics to study prokaryotic communities in complicated environments such as soils or animal intestines are shown. The role of relic DNA in the metagenome and the possibilities to study ancient organisms are highlighted. Particular attention is paid to the criticism of metagenomic technologies related to the low reproducibility of the sequencing data. Common methodological mistakes in bioinformatics processing of metagenomic data leading to misleading results are considered.

Exploring the Distinct Distribution of Archaeal Communities in Sites Contaminated with Explosives

Most of the research on bioremediation and estimation of microbial diversity in waste contaminated sites is focused on the domain Bacteria, whereas details on the relevance of Archaea are still lacking. The present study examined the archaeal diversity and predicted metabolic pathways in two discrete sites (SITE1 and SITE2) contaminated with explosives (RDX and HMX) by amplicon-targeted sequencing of 16S rRNA genes. In total, 14 soil samples were processed, and 35,758 OTUs were observed, among which 981 OTUs were classified as Archaea, representing ~2.7% of the total microbial diversity in our samples. The majority of OTUs belonged to phyla Euryarchaeota (~49%), Crenarchaeota (~24%), and Thaumarchaeota (~23%), while the remaining (~4%) OTUs were affiliated to Candidatus Parvarchaeota, Candidatus Aenigmarchaeota, and Candidatus Diapherotrites. The comparative studies between explosives contaminated and agricultural soil samples (with no history of explosives contamination) displayed significant differences between the compositions of the archaeal communities. Further, the metabolic pathways pertaining to xenobiotic degradation were presumably more abundant in the contaminated sites. Our data provide a first comprehensive report of archaeal communities in explosives contaminated sites and their putative degradation role in such ecosystems which have been as yet unexplored.

High Abundance of Thaumarchaeota Found in Deep Metamorphic Subsurface in Eastern China

Members of the Thaumarchaeota phylum play a key role in nitrogen cycling and are prevalent in a variety of environments including soil, sediment, and seawater. However, few studies have shown the presence of Thaumarchaeota in the terrestrial deep subsurface. Using high-throughput 16S rRNA gene sequencing, this study presents evidence for the high relative abundance of Thaumarchaeota in a biofilm sample collected from the well of Chinese Continental Scientific Drilling at a depth of 2000 m. Phylogenetic analysis showed a close relationship of these thaumarchaeotal sequences with known ammonia-oxidizing archaea (AOA) isolates, suggesting the presence of AOA in the deep metamorphic environment of eastern China which is believed to be oxic. Based on fluid geochemistry and FAProTax functional prediction, a pathway of nitrogen cycling is proposed. Firstly, heterotrophic nitrogen fixation is executed by diazotrophic bacteria coupled with methane oxidation. Then, ammonia is oxidized to nitrite by AOA, and nitrite is further oxidized to nitrate by bacteria within the phylum Nitrospirae. Denitrification and anaerobic ammonia oxidation occur slowly, leading to nitrate accumulation in the subsurface. With respect to biogeochemistry, the reaction between downward diffusing O2 and upward diffusing CH4 potentially fuels the ecosystem with a high relative abundance of Thaumarchaeota.

Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms during wastewater treatment processes

Studies on antibiotic removal during wastewater treatment processes are crucial since their release into the environment could bring potential threats to human health and ecosystem. Cometabolic biodegradation of antibiotics by ammonia oxidizing microorganisms (AOMs) has received special attentions due to the enhanced removal of antibiotics during nitrification processes. However, the interactions between antibiotics and AOMs are less well-elucidated. In this review, the recent research proceedings on cometabolic biodegradation of antibiotics by AOMs were summarized. Ammonia oxidizing bacteria (AOB), ammonia oxidizing archaea (AOA) and complete ammonia oxidizers (comammox) played significant roles in both nitrification and cometabolic biodegradation of antibiotics. Antibiotics at varying concentrations might pose inhibiting or stimulating effect on AOMs, influencing the microbial activity, community abundance and ammonia monooxygenase subunit A gene expression level. AOMs-induced cometabolic biodegradation products were analyzed as well as the corresponding pathways for each type of antibiotics. The effects of ammonium availability, initial antibiotic concentration, sludge retention time and temperature were assessed on the cometabolic biodegradation efficiencies of antibiotics. This work might provide further insights into the fate and removal of antibiotics during nitrification processes.

Trends in Microbial Community Composition and Function by Soil Depth

Microbial communities play important roles in soil health, contributing to processes such as the turnover of organic matter and nutrient cycling. As soil edaphic properties such as chemical composition and physical structure change from surface layers to deeper ones, the soil microbiome similarly exhibits substantial variability with depth, with respect to both community composition and functional profiles. However, soil microbiome studies often neglect deeper soils, instead focusing on the top layer of soil. Here, we provide a synthesis on how the soil and its resident microbiome change with depth. We touch upon soil physicochemical properties, microbial diversity, composition, and functional profiles, with a special emphasis on carbon cycling. In doing so, we seek to highlight the importance of incorporating analyses of deeper soils in soil studies.

METABOLIC: high-throughput profiling of microbial genomes for functional traits, metabolism, biogeochemistry, and community-scale functional networks

BACKGROUND

Advances in microbiome science are being driven in large part due to our ability to study and infer microbial ecology from genomes reconstructed from mixed microbial communities using metagenomics and single-cell genomics. Such omics-based techniques allow us to read genomic blueprints of microorganisms, decipher their functional capacities and activities, and reconstruct their roles in biogeochemical processes. Currently available tools for analyses of genomic data can annotate and depict metabolic functions to some extent; however, no standardized approaches are currently available for the comprehensive characterization of metabolic predictions, metabolite exchanges, microbial interactions, and microbial contributions to biogeochemical cycling.

RESULTS

We present METABOLIC (METabolic And BiogeOchemistry anaLyses In miCrobes), a scalable software to advance microbial ecology and biogeochemistry studies using genomes at the resolution of individual organisms and/or microbial communities. The genome-scale workflow includes annotation of microbial genomes, motif validation of biochemically validated conserved protein residues, metabolic pathway analyses, and calculation of contributions to individual biogeochemical transformations and cycles. The community-scale workflow supplements genome-scale analyses with determination of genome abundance in the microbiome, potential microbial metabolic handoffs and metabolite exchange, reconstruction of functional networks, and determination of microbial contributions to biogeochemical cycles. METABOLIC can take input genomes from isolates, metagenome-assembled genomes, or single-cell genomes. Results are presented in the form of tables for metabolism and a variety of visualizations including biogeochemical cycling potential, representation of sequential metabolic transformations, community-scale microbial functional networks using a newly defined metric "MW-score" (metabolic weight score), and metabolic Sankey diagrams. METABOLIC takes ~ 3 h with 40 CPU threads to process ~ 100 genomes and corresponding metagenomic reads within which the most compute-demanding part of hmmsearch takes ~ 45 min, while it takes ~ 5 h to complete hmmsearch for ~ 3600 genomes. Tests of accuracy, robustness, and consistency suggest METABOLIC provides better performance compared to other software and online servers. To highlight the utility and versatility of METABOLIC, we demonstrate its capabilities on diverse metagenomic datasets from the marine subsurface, terrestrial subsurface, meadow soil, deep sea, freshwater lakes, wastewater, and the human gut.

CONCLUSION

METABOLIC enables the consistent and reproducible study of microbial community ecology and biogeochemistry using a foundation of genome-informed microbial metabolism, and will advance the integration of uncultivated organisms into metabolic and biogeochemical models. METABOLIC is written in Perl and R and is freely available under GPLv3 at https://github.com/AnantharamanLab/METABOLIC . Video abstract.

Mangrove microbiota along the urban-to-rural gradient of the Cayenne estuary (French Guiana, South America): Drivers and potential bioindicators

The microbial communities inhabiting the Atlantic-East Pacific (AEP) mangroves have been poorly studied, and mostly comprise chronically polluted mangroves. In this study, we characterized changes in the structure and diversity of microbial communities of mangroves along the urban-to-rural gradient of the Cayenne estuary (French Guiana, South America) that experience low human impact. The microbial communities were assigned into 50 phyla. Proteobacteria, Chloroflexi, Acidobacteria, Bacteroidetes, and Planctomycetes were the most abundant taxa. The environmental determinants found to significantly correlated to the microbial communities at these mangroves were granulometry, dieldrin concentration, pH, and total carbon (TC) content. Furthermore, a precise analysis of the sediment highlights the existence of three types of anthropogenic pressure among the stations: (i) organic matter (OM) enrichment due to the proximity to the city and its wastewater treatment plant, (ii) dieldrin contamination, and (iii) naphthalene contamination. These forms of weak anthropogenic pressure seemed to impact the bacterial population size and microbial assemblages. A decrease in Bathyarchaeota, "Candidatus Nitrosopumilus", and Nitrospira genera was observed in mangroves subjected to OM enrichment. Mangroves polluted with organic contaminants were enriched in Desulfobacteraceae, Desulfarculaceae, and Acanthopleuribacteraceae (with dieldrin or polychlorobiphenyl contamination), and Chitinophagaceae and Geobacteraceae (with naphthalene contamination). These findings provide insights into the main environmental factors shaping microbial communities of mangroves in the AEP that experience low human impact and allow for the identification of several potential microbial bioindicators of weak anthropogenic pressure.

Microbial Nitrogen Transformation Potential in Sediments of Two Contrasting Lakes Is Spatially Structured but Seasonally Stable

The nitrogen (N) cycle is of global importance, as N is an essential element and a limiting nutrient in terrestrial and aquatic ecosystems. Excessive anthropogenic N fertilizer usage threatens sensitive downstream aquatic ecosystems. Although freshwater lake sediments remove N through various microbially mediated processes, few studies have investigated the microbial communities involved. In an integrated biogeochemical and microbiological study on a eutrophic and oligotrophic lake, we estimated N removal rates from pore water concentration gradients in sediments. Simultaneously, the abundance of different microbial N transformation genes was investigated using metagenomics on a seasonal and spatial scale. We observed that contrasting nutrient concentrations in sediments were associated with distinct microbial community compositions and significant differences in abundances of various N transformation genes. For both characteristics, we observed a more pronounced spatial than seasonal variability within each lake. The eutrophic Lake Baldegg showed a higher denitrification potential with higher nosZ gene (N₂O reductase) abundances and higher nirS:nirK (nitrite reductase) ratios, indicating a greater capacity for complete denitrification. Correspondingly, this lake had a higher N removal efficiency. The oligotrophic Lake Sarnen, in contrast, had a higher potential for nitrification. Specifically, it harbored a high abundance of Nitrospira, including some with the potential for comammox. Our results demonstrate that knowledge of the genomic N transformation potential is important for interpreting N process rates and understanding how the lacustrine sedimentary N cycle responds to variations in trophic conditions.

IMPORTANCE Anthropogenic nitrogen (N) inputs can lead to eutrophication in surface waters, especially in N-limited coastal ecosystems. Lakes effectively remove reactive N by transforming it to N₂ through microbial denitrification or anammox. The rates and distributions of these microbial processes are affected by factors such as the amount and quality of settling organic material and nitrate concentrations. However, the microbial communities mediating these N transformation processes in freshwater lake sediments remain largely unknown. We provide the first seasonally and spatially resolved metagenomic analysis of the N cycle in sediments of two lakes with different trophic states. We show that lakes with different trophic states select for distinct communities of N-cycling microorganisms with contrasting functional potentials for N transformation.

Changes in Archaeal Community and Activity by the Invasion of Spartina anglica Along Soil Depth Profiles of a Coastal Wetland

Invasion of Spartina spp. in tidal salt marshes may affect the function and characteristics of the ecosystem. Previous studies reported that the invasion alters biogeochemical and microbial processes in marsh ecosystems, yet our knowledge of changing archaeal community due to the invasion is still limited, whereas archaeal communities play a pivotal role in biogeochemical cycles within highly reduced marsh soils. In this study, we aimed to illustrate the influences of the Spartina anglica invasion on soil archaeal community and the depth profile of the influences. The relative abundance of archaeal phyla demonstrated that the invasion substantially shifted the characteristics of tidal salt marsh from marine to terrestrial soil only in surface layer, while the influences indirectly propagated to the deeper soil layer. In particular, two archaeal phyla, Asgardaeota and Diapherotrites, were strongly influenced by the invasion, indicating a shift from marine to terrestrial archaeal communities. The shifts in soil characteristics spread to the deeper soil layer that results in indirect propagation of the influences of the invasion down to the deeper soil, which was underestimated in previous studies. The changes in the concentration of dissolved organic carbon and salinity were the substantial regulating factors for that. Therefore, changes in biogeochemical and microbial characteristics in the deep soil layer, which is below the root zone of the invasive plant, should be accounted for a more accurate illustration of the consequences of the invasion.

Depth-structuring of multi-kingdom soil communities in agricultural pastures

The biodiversity and structure of deep agricultural soil communities are poorly understood, especially for eukaryotes. Using DNA metabarcoding and co-occurrence networks, we tested whether prokaryote, fungal, protist, and nematode biodiversity declines with increasing depth (0-0.1,  0.3-0.5,  and 1.1-1.7m) in pastoral soil; whether deep soil organisms are subsets of those at the surface; and whether multi-kingdom networks become more interconnected with increasing depth. Depth-related richness declines were observed for almost all detected fungal classes, protist phyla, and nematode orders, but only 13 of 25 prokaryote phyla, of which nine had increasing richness with depth. Deep soil communities were not simply subsets of surface communities, with 3.8%-12.2% of eukaryotes and 13.2% of prokaryotes detected only in the deepest samples. Eukaryotes mainly occurred in the upper soil layers whereas prokaryotes were more evenly distributed across depths. Plant-feeding nematodes were most abundant in top soil, whereas bacteria feeders were more abundant in deep soil. Co-occurrence network structure differences suggested that deep soil communities are concentrated around scarce niches of resource availability, in contrast to more spatially homogenous and abundant resources at the surface. Together, these results demonstrate effects of depth on the composition, distribution, and structure of prokaryote and eukaryote soil communities.

Rapid initiation of methanogenesis in the anaerobic digestion of food waste by acclimatizing sludge with sulfidated nanoscale zerovalent iron

Although coupling of sulfidated nanoscale zero-valent iron (S-nZVI) into anaerobic digestion of food waste (FW) for improving methanogenesis has been reported, the specific role of S-nZVI during start-up process and its influence on subsequent methanogenesis and system stability remains unknown. In this study, S-nZVI was added into the unacclimatized sludge system to investigate its influence on microbial acclimatization and methanogenic performance. During acclimatization phase, CH₄ production improved and VFAs transformation facilitated with the addition of S-nZVI. Furthermore, enzymatic activity analysis and electrochemical measurements presented direct evidence that electron transfer capacity of acclimatized sludge was significantly improved. S-nZVI favored the transition of microbial community to a robust and specialized population. During evaluation phase, acclimatized sludge still exhibited strong methanogenic ability, but the microbial community inevitably changed under the stress of FW. This research provides a novel perspective on initiating anaerobic digestion of FW for shorter start-up time and stronger methanogenesis.

Effects of design parameters, microbial community and nitrogen removal on the field-scale multi-pond constructed wetlands

Ecological multi-pond constructed wetlands (CWs) are an alternative wastewater treatment technology for nitrogen removal from non-point source pollution. As an important component of nitrogen cycles in the field-scale CWs, microorganisms are affected by design parameters. Nevertheless, the mechanism of design parameters affecting the distribution of microbial community and removal performance remains largely unexplored. In this study, satisfactory nitrogen removal performance was obtained in three multi-pond CWs. The highest mass removal rate per square meter (1104.0 mg/m²/day) and mass removal rate per cubic meter (590.2 mg/m³/day) for total nitrogen removal were obtained in the XY CW system during the wet season. The changes in seasonal parameters accounted for different removal performances and distributions of the microbial community. The combination of wastewater treatment technologies in the XY CW system consisting of ponds, CWs, and eco-floating treatment wetlands enriched the abundances of nitrogen-related functional genera. Correlation network analysis further demonstrated that longer hydraulic residence time and higher nitrogen concentration could intensify the enrichment of nitrogen-related functional genera. Regulating the combination of wastewater treatment technologies, the nitrogen concentration of influent, hydraulic loading rate, and water depth might promote the accumulation of microbial communities and enhance nitrogen removal. Macroscopical spatial/temporal regulation were proposed to enhance the treatment of non-point source pollution. The clarification of driving mechanism on design parameters, microbial community, and removal performance provided a novel perspective on the long-term maintenance of purification performance, practically sustainable applications, and scientific management of field-scale multi-pond CWs.