Global patterns of diversity and metabolism of microbial communities in deep-sea hydrothermal vent deposits

Earth's most needed uncultivated aquatic prokaryotes

Aquatic ecosystems house a significant fraction of Earth's biosphere, yet most prokaryotes inhabiting these environments remain uncultivated. While recently developed genome-resolved metagenomics and single-cell genomics techniques have underscored the immense genetic breadth and metabolic potential residing in uncultivated Bacteria and Archaea, cultivation of these microorganisms is required to study their physiology via genetic systems, confirm predicted biochemical pathways, exploit biotechnological potential, and accurately appraise nutrient turnover. Over the past two decades, the limitations of culture-independent investigations highlighted the importance of cultivation in bridging this vast knowledge gap. Here, we collected more than 80 highly sought-after uncultivated lineages of aquatic Bacteria and Archaea with global ecological impact. In addition to fulfilling critical roles in global carbon, nitrogen, and sulfur cycling, many of these organisms are thought to partake in key symbiotic relationships. This review highlights the vital contributions of uncultured microbes in aquatic ecosystems, from lakes and groundwater to the surfaces and depths of the oceans and will guide current and future initiatives tasked with cultivating our planet's most elusive, yet highly consequential aquatic microflora.

Synergetic effects of chlorinated paraffins and microplastics on microbial communities and nitrogen cycling in deep-sea cold seep sediments

Chlorinated paraffins (CPs) and microplastics (MPs) are commonly found in deep-sea cold seep sediments, where nitrogen cycling processes frequently occur. However, little is known about their combined effects on sedimentary microbial communities and nitrogen cycling in these environments. This study aimed to investigate the synergistic impacts of CPs and MPs on microbial communities and nitrogen cycling in deep-sea cold seep sediments through microcosm experiments. Our results demonstrated that the presence of CPs and MPs induced significant alterations in microbial community composition, promoting the growth of Halomonas. Furthermore, CPs and MPs were found to enhance nitrification, denitrification and anammox processes, which was evidenced by the higher abundance of genes associated with nitrification and denitrification, as well as increased activity of denitrification and anammox in the CPs and MPs-treatment groups compared to the control group. Additionally, the enhanced influence of CPs and MPs on denitrification was expected to promote nitrate-dependent and sulfate-dependent anaerobic oxidation of methane, thereby resulting in less methane released into the environment. These findings shed light on the potential consequences of simultaneous exposure to CPs and MPs on biogeochemical nitrogen cycling in deep-sea cold seep sediments.

Significant correlations between heavy metals and prokaryotes in the Okinawa Trough hydrothermal sediments

Prokaryotes play crucial roles in hydrothermal vent ecosystems, yet their interactions with heavy metals are not well understood. This study explored the diversity of prokaryotic communities and their correlations with heavy metals and nutrient elements in hydrothermal sediments from Okinawa Trough. A total of 117 bacterial genera in 26 bacterial phyla and 10 archaeal classes in 3 archaeal phyla were identified, including dominant prokaryotic phyla Planctomycetes, Acidobacteria, Verrucomicrobia, and Euryarchaeota. Furthermore, Fe (39.61 mg/g), Mn (2.84 mg/g) and Ba (0.36 mg/g) were found to be the most abundant heavy metals in the Okinawa hydrothermal sediments. Notably, the concentrations of Zn, Ba, Mn, total organic carbon, and total nitrogen significantly increased, whereas the total sulfur concentration distinctively decreased at sampling sites farther from hydrothermal vents. These changes corresponded with reductions in prokaryotic abundance and diversity. Most heavy metals, including Mn, Fe, Co, Cu and As, presented significant positive correlations with a number of prokaryotic genera in the nearby sediment samples. In contrast, both positive and negative correlations with prokaryotes were observed in remote sediment. The keystone taxa include Magnetospirillum, GOUTA19, Lysobacter, Kaistobacter, Treponema, and Clostridium were detected through prokaryote interspecies interactions. The functional predictions revealed significant genes involved in carbon fixation, nitrogen/sulfur cycling, heat shock protein, and metal resistance pathways. Structural equation modeling confirmed that metal and nutrient elements directly influence the composition of prokaryotic communities, which in turn affects the relative abundance of functional genes.

Deep-sea microorganisms-driven V5+ and Cd2+ removal from vanadium smelting wastewater: Bacterial screening, performance and mechanism

The disorderly discharge of industrial wastewater containing heavy metals has caused serious water pollution and ecological environmental risks, ultimately threatening human life and health. Biological treatment methods have obvious advantages, but the existing microorganisms exhibit issues such as poor resistance, adaptability, colonization ability, and low activity. However, a wide variety of microorganisms in deep-sea hydrothermal vent areas are tolerant to heavy metals, possessing the potential for efficient treatment of heavy metal wastewater. Based on this, the study obtained a group of deep-sea microbial communities dominated by Burkholderia-Caballeronia-Paraburkholderia through shake flask experiments from the sediments of deep-sea hydrothermal vents, which can simultaneously achieve the synchronous removal of vanadium and cadmium heavy metals through bioreduction, biosorption, and biomineralization. Through SEM-EDS, XRD, XPS, and FT-IR analyses, it was found that V(V) was reduced to V(IV) through a reduction process and subsequently precipitated. Glucose oxidation accelerated this process. Cd(II) underwent biomineralization to form precipitates such as cadmium hydroxide and cadmium carbonate. Functional groups on the microbial cell surface, such as -CH2, C=O, N-H, -COOH, phosphate groups, amino groups, and M-O moieties, participated in the bioadsorption processes of V(V) and Cd(II) heavy metals. Under optimal conditions, namely a temperature of 40 °C, pH value of 7.5, inoculation amount of 10%, salinity of 4%, COD concentration of 600 mg/L, V5+ concentration of 300 mg/L, and Cd2+ concentration of 40 mg/L, the OD600 can reach its highest at 72 h, with the removal efficiency of V5+, Cd2+, and COD in simulated vanadium smelting wastewater reaching 86.32%, 59.13%, and 61.63%, respectively. This study provides theoretical insights and practical evidence for understanding the dynamic changes in microbial community structure under heavy metal stress, as well as the resistance mechanisms of microbial treatment of industrial heavy metal wastewater.

Diversity and ecology of microbial sulfur metabolism

Sulfur plays a pivotal role in interactions within the atmosphere, lithosphere, pedosphere, hydrosphere and biosphere, and the functioning of living organisms. In the Earth's crust, mantle, and atmosphere, sulfur undergoes geochemical transformations due to natural and anthropogenic factors. In the biosphere, sulfur participates in the formation of amino acids, proteins, coenzymes and vitamins. Microorganisms in the biosphere are crucial for cycling sulfur compounds through oxidation, reduction and disproportionation reactions, facilitating their bioassimilation and energy generation. Microbial sulfur metabolism is abundant in both aerobic and anaerobic environments and is interconnected with biogeochemical cycles of important elements such as carbon, nitrogen and iron. Through metabolism, competition or cooperation, microorganisms metabolizing sulfur can drive the consumption of organic carbon, loss of fixed nitrogen and production of climate-active gases. Given the increasing significance of sulfur metabolism in environmental alteration and the intricate involvement of microorganisms in sulfur dynamics, a timely re-evaluation of the sulfur cycle is imperative. This Review explores our understanding of microbial sulfur metabolism, primarily focusing on the transformations of inorganic sulfur. We comprehensively overview the sulfur cycle in the face of rapidly changing ecosystems on Earth, highlighting the importance of microbially-mediated sulfur transformation reactions across different environments, ecosystems and microbiomes.

Unveiling the microbial diversity across the northern Ninety East Ridge in the Indian Ocean

Prokaryotes play a crucial role in marine ecosystem health and drive biogeochemical processes. The northern Ninety East Ridge (NER) of the Indian Ocean, a pivotal yet understudied area for these cycles, has been the focus of our study. We employed high-throughput 16S rRNA gene sequencing to analyze 35 water samples from five stations along the ridge, categorized into three depth- and dissolved oxygen-level-based groups. Our approach uncovered a clear stratification of microbial communities, with key bioindicators such as Prochlorococcus MIT9313, Sva0996 marine group, and Candidatus Actinomarina in the upper layer; Ketobacter, Pseudophaeobacter, Nitrospina, and SAR324 clade in the middle layer; and Methylobacterium-Methylorubrum, Sphingomonas, Sphingobium, and Erythrobacter in the deep layer. Methylobacterium-Methylorubrum emerged as the most abundant bacterial genus, while Nitrosopumilaceae predominated among archaeal communities. The spatial and depth-wise distribution patterns revealed that Ketobacter was unique to the northern NER, whereas Methylobacterium-Methylorubrum, UBA10353, SAR324 clade, SAR406, Sva0996_marine_group, Candidatus Actinomarina were ubiquitous across various marine regions, exhibiting niche differentiation at the OTU level. Environmental factors, especially dissolved oxygen (DO), silicate, nitrate, and salinity, significantly influence community structure. These findings not only reveal the novelty and adaptability of the microbial ecosystem in the northern NER but also contribute to the broader understanding of marine microbial diversity and its response to environmental heterogeneity.

Ignisphaera cupida sp. nov., a hyperthermophilic hydrolytic archaeon from a hot spring of Uzon (Kamchatka), and emended description of the genus Ignisphaera

A novel strictly anaerobic hyperthermophilic archaeon, strain 4213-coT, was isolated from a terrestrial hot spring in the Uzon Caldera, Kamchatka (Russian Federation). Coccoid cells were present singly, in pairs, or aggregates, and occasionally were motile. The strain grew at 75-100 °C and within a pH range of 5.4-8.2 with the optimum at 92 °C and pH 6.4-6.7. Strain 4213-coT was a chemoorganoheterotroph, growing on proteinaceous substrates and mono-, di- and polysaccharides (starch, guar gum, xanthan gum). It did not require sodium chloride for growth. The complete genome of strain 4213-coT was 1.74 Mbp in size; its G+C content was 36.18 %. Genome analysis allowed to identify 25 genes encoding glycosidases involved in polysaccharide hydrolysis as well as genes of ADP-forming acetate-CoA ligase, lactate dehydrogenase and two [NiFe] hydrogenases responsible for acetate, lactate and hydrogen formation during fermentation. Moreover gene cluster encoding archaellum subunits was found. According to the phylogenomic analysis strain 4213-coT formed a species-level phylogenetic lineage within Ignisphaera genus. Our phylogenomic analysis also supports the delineation of the Ignisphaera genus into a separate family Ignisphaeraceae, as recently published. Here we propose a novel species Ignisphaera cupida, sp. nov. with type strain 4213-coT (=JCM 39446T=VKM B-3715T=UQM 41593T). Ecogenomic analysis showed that representatives of the Ignisphaera are thermophilic archaea, the majority of them were found in terrestrial hot springs and deep-sea hydrothermal vents. This study allowed a better understanding of physiology and ecology of Ignisphaeraceae - a rather understudied archaeal group.

Covariation of hot spring geochemistry with microbial genomic diversity, function, and evolution

The geosphere and the microbial biosphere have co-evolved for ~3.8 Ga, with many lines of evidence suggesting a hydrothermal habitat for life's origin. However, the extent that contemporary thermophiles and their hydrothermal habitats reflect those that likely existed on early Earth remains unknown. To address this knowledge gap, 64 geochemical analytes were measured and 1022 metagenome-assembled-genomes (MAGs) were generated from 34 chemosynthetic high-temperature springs in Yellowstone National Park and analysed alongside 444 MAGs from 35 published metagenomes. We used these data to evaluate co-variation in MAG taxonomy, metabolism, and phylogeny as a function of hot spring geochemistry. We found that cohorts of MAGs and their functions are discretely distributed across pH gradients that reflect different geochemical provinces. Acidic or circumneutral/alkaline springs harbor MAGs that branched later and are enriched in sulfur- and arsenic-based O2-dependent metabolic pathways that are inconsistent with early Earth conditions. In contrast, moderately acidic springs sourced by volcanic gas harbor earlier-branching MAGs that are enriched in anaerobic, gas-dependent metabolisms (e.g. H2, CO2, CH4 metabolism) that have been hypothesized to support early microbial life. Our results provide insight into the influence of redox state in the eco-evolutionary feedbacks between thermophiles and their habitats and suggest moderately acidic springs as early Earth analogs.

Microbial metabolic potential of hydrothermal vent chimneys along the submarine ring of fire

Hydrothermal vents host a diverse community of microorganisms that utilize chemical gradients from the venting fluid for their metabolisms. The venting fluid can solidify to form chimney structures that these microbes adhere to and colonize. These chimney structures are found throughout many different locations in the world's oceans. In this study, comparative metagenomic analyses of microbial communities on five chimney structures from around the Pacific Ocean were elucidated focusing on the core taxa and genes that are characteristic of each of these hydrothermal vent chimneys. The differences among the taxa and genes found at each chimney due to parameters such as physical characteristics, chemistry, and activity of the vents were highlighted. DNA from the chimneys was sequenced, assembled into contigs, and annotated for gene function. Genes used for carbon, oxygen, sulfur, nitrogen, iron, and arsenic metabolisms were found at varying abundances at each of the chimneys, largely from either Gammaproteobacteria or Campylobacteria. Many taxa shared an overlap of these functional metabolic genes, indicating that functional redundancy is critical for life at these hydrothermal vents. A high relative abundance of oxygen metabolism genes coupled with a low abundance of carbon fixation genes could be used as a unique identifier for inactive chimneys. Genes used for DNA repair, chemotaxis, and transposases were found at high abundances at each of these hydrothermal chimneys allowing for enhanced adaptations to the ever-changing chemical and physical conditions encountered.

Metabolic adaptations underpin high productivity rates in relict subsurface water

Groundwater aquifers are ecological hotspots with diverse microbes essential for biogeochemical cycles. Their ecophysiology has seldom been studied on a basin scale. In particular, our knowledge of chemosynthesis in the deep aquifers where temperatures reach 60 °C, is limited. Here, we investigated the diversity, activity, and metabolic potential of microbial communities from nine wells reaching ancient groundwater beneath Israel's Negev Desert, spanning two significant, deep (up to 1.5 km) aquifers, the Judea Group carbonate and Kurnub Group Nubian sandstone that contain fresh to brackish, hypoxic to anoxic water. We estimated chemosynthetic productivity rates ranging from 0.55 ± 0.06 to 0.82 ± 0.07 µg C L-1 d-1 (mean ± SD), suggesting that aquifer productivity may be underestimated. We showed that 60% of MAGs harbored genes for autotrophic pathways, mainly the Calvin-Benson-Bassham cycle and the Wood-Ljungdahl pathway, indicating a substantial chemosynthetic capacity within these microbial communities. We emphasize the potential metabolic versatility in the deep subsurface, enabling efficient carbon and energy use. This study set a precedent for global aquifer exploration, like the Nubian Sandstone Aquifer System in the Arabian and Western Deserts, and reconsiders their role as carbon sinks.

Panera: An innovative framework for surmounting uncertainty in microbial community modeling using pan-genera metabolic models

Utilization of 16S rRNA data in constraint-based modeling to characterize microbial communities confronts a major hurdle of lack of species-level resolution, impeding the construction of community models. We introduce "Panera," an innovative framework designed to model communities under this uncertainty and yet perform metabolic inferences using pan-genus metabolic models (PGMMs). We demonstrated PGMMs' utility for comprehending the metabolic capabilities of a genus and in characterizing community models using amplicon data. The unique, adaptable nature of PGMMs unlocks their potential in building hybrid communities, combining genome-scale metabolic models (GSMMs) and PGMMs. Notably, these models provide predictions comparable to the standard GSMM-based community models, while achieving a nearly 46% reduction in error compared to the genus model-based communities. In essence, "Panera" presents a potent and effective approach to aid in metabolic modeling by enabling robust predictions of community metabolic potential when dealing with amplicon data, and offers insights into genus-level metabolic landscapes.

Cultivation of novel Atribacterota from oil well provides new insight into their diversity, ecology, and evolution in anoxic, carbon-rich environments

BACKGROUND

The Atribacterota are widely distributed in the subsurface biosphere. Recently, the first Atribacterota isolate was described and the number of Atribacterota genome sequences retrieved from environmental samples has increased significantly; however, their diversity, physiology, ecology, and evolution remain poorly understood.

RESULTS

We report the isolation of the second member of Atribacterota, Thermatribacter velox gen. nov., sp. nov., within a new family Thermatribacteraceae fam. nov., and the short-term laboratory cultivation of a member of the JS1 lineage, Phoenicimicrobium oleiphilum HX-OS.bin.34TS, both from a terrestrial oil reservoir. Physiological and metatranscriptomics analyses showed that Thermatribacter velox B11T and Phoenicimicrobium oleiphilum HX-OS.bin.34TS ferment sugars and n-alkanes, respectively, producing H2, CO2, and acetate as common products. Comparative genomics showed that all members of the Atribacterota lack a complete Wood-Ljungdahl Pathway (WLP), but that the Reductive Glycine Pathway (RGP) is widespread, indicating that the RGP, rather than WLP, is a central hub in Atribacterota metabolism. Ancestral character state reconstructions and phylogenetic analyses showed that key genes encoding the RGP (fdhA, fhs, folD, glyA, gcvT, gcvPAB, pdhD) and other central functions were gained independently in the two classes, Atribacteria (OP9) and Phoenicimicrobiia (JS1), after which they were inherited vertically; these genes included fumarate-adding enzymes (faeA; Phoenicimicrobiia only), the CODH/ACS complex (acsABCDE), and diverse hydrogenases (NiFe group 3b, 4b and FeFe group A3, C). Finally, we present genome-resolved community metabolic models showing the central roles of Atribacteria (OP9) and Phoenicimicrobiia (JS1) in acetate- and hydrocarbon-rich environments.

CONCLUSION

Our findings expand the knowledge of the diversity, physiology, ecology, and evolution of the phylum Atribacterota. This study is a starting point for promoting more incisive studies of their syntrophic biology and may guide the rational design of strategies to cultivate them in the laboratory. Video Abstract.

Analysis of nearly 3000 archaeal genomes from terrestrial geothermal springs sheds light on interconnected biogeochemical processes

Terrestrial geothermal springs are physicochemically diverse and host abundant populations of Archaea. However, the diversity, functionality, and geological influences of these Archaea are not well understood. Here we explore the genomic diversity of Archaea in 152 metagenomes from 48 geothermal springs in Tengchong, China, collected from 2016 to 2021. Our dataset is comprised of 2949 archaeal metagenome-assembled genomes spanning 12 phyla and 392 newly identified species, which increases the known species diversity of Archaea by ~48.6%. The structures and potential functions of the archaeal communities are strongly influenced by temperature and pH, with high-temperature acidic and alkaline springs favoring archaeal abundance over Bacteria. Genome-resolved metagenomics and metatranscriptomics provide insights into the potential ecological niches of these Archaea and their potential roles in carbon, sulfur, nitrogen, and hydrogen metabolism. Furthermore, our findings illustrate the interplay of competition and cooperation among Archaea in biogeochemical cycles, possibly arising from overlapping functional niches and metabolic handoffs. Taken together, our study expands the genomic diversity of Archaea inhabiting geothermal springs and provides a foundation for more incisive study of biogeochemical processes mediated by Archaea in geothermal ecosystems.

Impact of Hydrostatic Pressure on Molecular Structure and Dynamics of the Sodium and Chloride Ions in Portlandite Nanopores

In order to address the issues of energy depletion, more resources are being searched for in the deep sea. Therefore, research into how the deep-sea environment affects cement-based materials for underwater infrastructure is required. This paper examines the impact of ocean depth (0, 500, 1000, and 1500 m) on the ion interaction processes in concrete nanopores using molecular dynamics simulations. At the portlandite interface, the local structural and kinetic characteristics of ions and water molecules are examined. The findings show that the portlandite surface hydrophilicity is unaffected by increasing depth. The density profile and coordination number of ions alter as depth increases, and the diffusion speed noticeably decreases. The main cause of the ions' reduced diffusion velocity is expected to be the low temperature. This work offers a thorough understanding of the cement hydration products' microstructure in deep sea, which may help explain why cement-based underwater infrastructure deteriorates over time.

Genomic comparison of deep-sea hydrothermal genera related to Aeropyrum, Thermodiscus and Caldisphaera, and proposed emended description of the family Acidilobaceae

Deep-sea hydrothermal vents host archaeal and bacterial thermophilic communities, including taxonomically and functionally diverse Thermoproteota. Despite their prevalence in high-temperature submarine communities, Thermoproteota are chronically under-represented in genomic databases and issues have emerged regarding their nomenclature, particularly within the Aeropyrum-Thermodiscus-Caldisphaera. To resolve some of these problems, we identified 47 metagenome-assembled genomes (MAGs) within this clade, from 20 previously published deep-sea hydrothermal vent and submarine volcano metagenomes, and 24 MAGs from public databases. Using phylogenomic analysis, Genome Taxonomy Database Toolkit (GTDB-Tk) taxonomic assessment, 16S rRNA gene phylogeny, average amino acid identity (AAI) and functional gene patterns, we re-evaluated of the taxonomy of the Aeropyrum-Thermodiscus-Caldisphaera. At least nine genus-level clades were identified with two or more MAGs. In accordance with SeqCode requirements and recommendations, we propose names for three novel genera, viz. Tiamatella incendiivivens, Hestiella acidicharens and Calypsonella navitae. A fourth genus was also identified related to Thermodiscus maritimus, for which no available sequenced genome exists. We propose the novel species Thermodiscus eudorianus to describe our high-quality Thermodiscus MAG, which represents the type genome for the genus. All three novel genera and T. eudorianus are likely anaerobic heterotrophs, capable of fermenting protein-rich carbon sources, while some Tiamatella, Calypsonella and T. eudorianus may also reduce polysulfides, thiosulfate, sulfur and/or selenite, and the likely acidophile, Hestiella, may reduce nitrate and/or perchlorate. Based on phylogenomic evidence, we also propose the family Acidilobaceae be amended to include Caldisphaera, Aeropyrum, Thermodiscus and Stetteria and the novel genera described here.

Deep-sea in situ and laboratory multi-omics provide insights into the sulfur assimilation of a deep-sea Chloroflexota bacterium

Chloroflexota bacteria are abundant and globally distributed in various deep-sea ecosystems. It has been reported based on metagenomics data that two deep-sea Chloroflexota lineages (the SAR202 group and Dehalococcoidia class) have the potential to drive sulfur cycling. However, the absence of cultured Chloroflexota representatives is a significant bottleneck toward understanding their contribution to the deep-sea sulfur cycling. In this study, we find that Phototrophicus methaneseepsis ZRK33 isolated from deep-sea sediment has a heterotrophic lifestyle and can assimilate sulfate and thiosulfate. Using combined physiological, genomic, proteomic, and in situ transcriptomic methods, we find that strain ZRK33 can perform assimilatory sulfate reduction in both laboratory and deep-sea conditions. Metabolism of sulfate or thiosulfate by strain ZRK33 significantly promotes the transport and degradation of various macromolecules and thereby stimulates the energy production. In addition, metagenomic results show that genes associated with assimilatory and dissimilatory sulfate reduction are ubiquitously distributed in the metagenome-assembled genomes of Chloroflexota members derived from deep-sea sediments. Metatranscriptomic results also show that the expression levels of related genes are upregulated, strongly suggesting that Chloroflexota bacteria may play undocumented roles in deep-sea sulfur cycling.

IMPORTANCE

The cycling of sulfur is one of Earth's major biogeochemical processes and is closely related to the energy metabolism of microorganisms living in the deep-sea cold seep and hydrothermal vents. To date, some of the members of Chloroflexota are proposed to play a previously unrecognized role in sulfur cycling. However, the sulfur metabolic characteristics of deep-sea Chloroflexota bacteria have never been reported, and remain to be verified in cultured deep-sea representatives. Here, we show that the deep-sea Chloroflexota bacterium ZRK33 can perform sulfate assimilation in both laboratory and deep-sea conditions, which expands our knowledge of the sulfur metabolic potential of deep-sea Chloroflexota bacteria. We also show that the genes associated with assimilatory and dissimilatory sulfate reduction ubiquitously distribute in the deep-sea Chloroflexota members, providing hints to the roles of Chloroflexota bacteria in deep-sea sulfur biogeochemical cycling.

Expanded Archaeal Genomes Shed New Light on the Evolution of Isoprenoid Biosynthesis

Isoprenoids and their derivatives, essential for all cellular life on Earth, are particularly crucial in archaeal membrane lipids, suggesting that their biosynthesis pathways have ancient origins and play pivotal roles in the evolution of early life. Despite all eukaryotes, archaea, and a few bacterial lineages being known to exclusively use the mevalonate (MVA) pathway to synthesize isoprenoids, the origin and evolutionary trajectory of the MVA pathway remain controversial. Here, we conducted a thorough comparison and phylogenetic analysis of key enzymes across the four types of MVA pathway, with the particular inclusion of metagenome assembled genomes (MAGs) from uncultivated archaea. Our findings support an archaeal origin of the MVA pathway, likely postdating the divergence of Bacteria and Archaea from the Last Universal Common Ancestor (LUCA), thus implying the LUCA's enzymatic inability for isoprenoid biosynthesis. Notably, the Asgard archaea are implicated in playing central roles in the evolution of the MVA pathway, serving not only as putative ancestors of the eukaryote- and Thermoplasma-type routes, but also as crucial mediators in the gene transfer to eukaryotes, possibly during eukaryogenesis. Overall, this study advances our understanding of the origin and evolutionary history of the MVA pathway, providing unique insights into the lipid divide and the evolution of early life.

Functional redundancy is the key mechanism used by microorganisms for nitrogen and sulfur metabolism during manure composting

The microbial ecological functions associated with the nitrogen and sulfur cycles during composting have not been thoroughly elucidated. Using metagenomic sequencing, the microbial mechanisms underlying the nitrogen and sulfur metabolism during livestock and poultry manure composting were investigated in this study. The findings demonstrate that functional redundancy among microorganisms is a crucial factor for the nitrogen and sulfur cycling during livestock and poultry manure composting. Processes such as organic sulfur synthesis, assimilatory sulfate reduction, ammonia assimilation, and denitrification were found to be prevalent. Additionally, there was a certain degree of conservation in nitrogen and sulfur conversion functions among microorganisms at the phylum level. All high-quality metagenomic assembly genomes (MAGs) possessed carbon fixation potential, with 86.3 % of MAGs containing both nitrogen and sulfur conversion genes. Except for bin30, other MAGs encoding sulfur oxidation enzymes were found to be associated with at least one denitrification gene. This suggests a potential interplay between nitrogen and sulfur metabolism among microorganisms. 45, 19, 1, 31, 1, and 2 MAGs could completely regulate organic sulfur synthesis, assimilatory sulfate reduction, thiosulfate oxidation to sulfate, glutamine synthase-glutamate synthase pathway (GS-GOGAT), denitrification, and dissimilatory nitrate reduction, respectively by encoding the required enzymes. TN and pH were the key factors driving the functional redundancy in nitrogen and sulfur microbial community.

Predicted metabolic roles and stress responses provide insights into candidate phyla Hydrogenedentota and Sumerlaeota as members of the rare biosphere in biofilms from various environments

Pustular mats from Shark Bay, Western Australia, host complex microbial communities bound within an organic matrix. These mats harbour many poorly characterized organisms with low relative abundances (<1%), such as candidate phyla Hydrogenedentota and Sumerlaeota. Here, we aim to constrain the metabolism and physiology of these candidate phyla by analyzing two representative metagenome-assembled genomes (MAGs) from a pustular mat. Metabolic reconstructions of these MAGs suggest facultatively anaerobic, chemoorganotrophic lifestyles of both organisms and predict that both MAGs can metabolize a diversity of carbohydrate substrates. Ca. Sumerlaeota possesses genes involved in degrading chitin, cellulose and other polysaccharides, while Ca. Hydrogenedentota can metabolize cellulose derivatives in addition to glycerol, fatty acids and phosphonates. Both Ca. phyla can respond to nitrosative stress and participate in nitrogen metabolism. Metabolic comparisons of MAGs from Shark Bay and those from various polyextreme environments (i.e., hot springs, hydrothermal vents, subsurface waters, anaerobic digesters, etc.) reveal similar metabolic capabilities and adaptations to hypersalinity, oxidative stress, antibiotics, UV radiation, nitrosative stress, heavy metal toxicity and life in surface-attached communities. These adaptations and capabilities may account for the widespread nature of these organisms and their contributions to biofilm communities in a range of extreme surface and subsurface environments.

Seafloor incubation experiments at deep-sea hydrothermal vents reveal distinct biogeographic signatures of autotrophic communities

The discharge of hydrothermal vents on the seafloor provides energy sources for dynamic and productive ecosystems, which are supported by chemosynthetic microbial populations. These populations use the energy gained by oxidizing the reduced chemicals contained within the vent fluids to fix carbon and support multiple trophic levels. Hydrothermal discharge is ephemeral and chemical composition of such fluids varies over space and time, which can result in geographically distinct microbial communities. To investigate the foundational members of the community, microbial growth chambers were placed within the hydrothermal discharge at Axial Seamount (Juan de Fuca Ridge), Magic Mountain Seamount (Explorer Ridge), and Kama'ehuakanaloa Seamount (Hawai'i hotspot). Campylobacteria were identified within the nascent communities, but different amplicon sequence variants were present at Axial and Kama'ehuakanaloa Seamounts, indicating that geography in addition to the composition of the vent effluent influences microbial community development. Across these vent locations, dissolved iron concentration was the strongest driver of community structure. These results provide insights into nascent microbial community structure and shed light on the development of diverse lithotrophic communities at hydrothermal vents.

The trade-off between individual metabolic specialization and versatility determines the metabolic efficiency of microbial communities

In microbial systems, a metabolic pathway can be either completed by one autonomous population or distributed among a consortium performing metabolic division of labor (MDOL). MDOL facilitates the system's function by reducing the metabolic burden; however, it may hinder the function by reducing the exchange efficiency of metabolic intermediates among individuals. As a result, the function of a community is influenced by the trade-offs between the metabolic specialization and versatility of individuals. To experimentally test this hypothesis, we deconstructed the naphthalene degradation pathway into four steps and introduced them individually or combinatorically into different strains with varying levels of metabolic specialization. Using these strains, we engineered 1,456 synthetic consortia and found that 74 consortia exhibited higher degradation function than both the autonomous population and rigorous MDOL consortium. Quantitative modeling provides general strategies for identifying the most effective MDOL configuration. Our study provides critical insights into the engineering of high-performance microbial systems.

Metagenomic Insights into Ecophysiology of Zetaproteobacteria and Gammaproteobacteria in Shallow Zones within Deep-sea Massive Sulfide Deposits

Deep-sea massive sulfide deposits serve as energy sources for chemosynthetic ecosystems in dark, cold environments even after hydrothermal activity ceases. However, the vertical distribution of microbial communities within sulfide deposits along their depth from the seafloor as well as their ecological roles remain unclear. We herein conducted a culture-independent metagenomic ana-lysis of a core sample of massive sulfide deposits collected in a hydrothermally inactive field of the Southern Mariana Trough, Western Pacific, by drilling (sample depth: 0.52‍ ‍m below the seafloor). Based on the gene context of the metagenome-assembled genomes (MAGs) obtained, we showed the metabolic potential of as-yet-uncultivated microorganisms, particularly those unique to the shallow zone rich in iron hydroxides. Some members of Gammaproteobacteria have potential for the oxidation of reduced sulfur species (such as sulfide and thiosulfate) to sulfate coupled to nitrate reduction to ammonia and carbon fixation via the Calvin-Benson-Bassham (CBB) cycle, as the primary producers. The Zetaproteobacteria member has potential for iron oxidation coupled with microaerobic respiration. A comparative ana-lysis with previously reported metagenomes from deeper zones (~2‍ ‍m below the seafloor) of massive sulfide deposits revealed a difference in the relative abundance of each putative primary producer between the shallow and deep zones. Our results expand knowledge on the ecological potential of uncultivated microorganisms in deep-sea massive sulfide deposits and provide insights into the vertical distribution patterns of chemosynthetic ecosystems.

A comprehensive overview of the Chloroflexota community in wastewater treatment plants worldwide

IMPORTANCE

Chloroflexota are often abundant members of the biomass in wastewater treatment plants (WWTPs) worldwide, typically with a filamentous morphology, forming the backbones of the activated sludge floc. However, their overgrowth can often cause operational issues connected to poor settling or foaming, impairing effluent quality and increasing operational costs. Despite their importance, few Chloroflexota genera have been characterized so far. Here, we present a comprehensive overview of Chloroflexota abundant in WWTPs worldwide and an in-depth characterization of their morphology, phylogeny, and ecophysiology, obtaining a broad understanding of their ecological role in activated sludge.

Viromes vs. mixed community metagenomes: choice of method dictates interpretation of viral community ecology

Background

Viruses, the majority of which are uncultivated, are among the most abundant biological entities on Earth. From altering microbial physiology to driving community dynamics, viruses are fundamental members of microbiomes. While the number of studies leveraging viral metagenomics (viromics) for studying uncultivated viruses is growing, standards for viromics research are lacking. Viromics can utilize computational discovery of viruses from total metagenomes of all community members (hereafter metagenomes) or use physical separation of virus-specific fractions (hereafter viromes). However, differences in the recovery and interpretation of viruses from metagenomes and viromes obtained from the same samples remain understudied.

Results

Here, we compare viral communities from paired viromes and metagenomes obtained from 60 diverse samples across human gut, soil, freshwater, and marine ecosystems. Overall, viral communities obtained from viromes were more abundant and species rich than those obtained from metagenomes, although there were some exceptions. Despite this, metagenomes still contained many viral genomes not detected in viromes. We also found notable differences in the predicted lytic state of viruses detected in viromes vs metagenomes at the time of sequencing. Other forms of variation observed include genome presence/absence, genome quality, and encoded protein content between viromes and metagenomes, but the magnitude of these differences varied by environment.

Conclusions

Overall, our results show that the choice of method can lead to differing interpretations of viral community ecology. We suggest that the choice of whether to target a metagenome or virome to study viral communities should be dependent on the environmental context and ecological questions being asked. However, our overall recommendation to researchers investigating viral ecology and evolution is to pair both approaches to maximize their respective benefits.

Novel Insights on the Bacterial and Archaeal Diversity of the Panarea Shallow-Water Hydrothermal Vent Field

Current knowledge of the microbial diversity of shallow-water hydrothermal vents is still limited. Recent evidence suggests that these peculiar and heterogeneous systems might host highly diversified microbial assemblages with novel or poorly characterized lineages. In the present work, we used 16S rRNA gene metabarcoding to provide novel insights into the diversity of the bacterial and archaeal assemblages in seawater and sediments of three shallow-water hydrothermal systems of Panarea Island (Tyrrhenian Sea). The three areas were characterized by hot, cold, or intermediate temperatures and related venting activities. Microbial biodiversity in seawater largely differed from the benthic one, both in α-diversity (i.e., richness of amplicon sequence variants-ASVs) and in prokaryotic assemblage composition. Furthermore, at the class level, the pelagic prokaryotic assemblages were very similar among sites, whereas the benthic microbial assemblages differed markedly, reflecting the distinct features of the hydrothermal activities at the three sites we investigated. Our results show that ongoing high-temperature emissions can influence prokaryotic α-diversity at the seafloor, increasing turnover (β-)diversity, and that the intermediate-temperature-venting spot that experienced a violent gas explosion 20 years ago now displays the highest benthic prokaryotic diversity. Overall, our results suggest that hydrothermal vent dynamics around Panarea Island can contribute to an increase in the local heterogeneity of physical-chemical conditions, especially at the seafloor, in turn boosting the overall microbial (γ-)diversity of this peculiar hydrothermal system.

Thermophilic methane oxidation is widespread in Aotearoa-New Zealand geothermal fields

Geothermal areas represent substantial point sources for greenhouse gas emissions such as methane. While it is known that methanotrophic microorganisms act as a biofilter, decreasing the efflux of methane in most soils to the atmosphere, the diversity and the extent to which methane is consumed by thermophilic microorganisms in geothermal ecosystems has not been widely explored. To determine the extent of biologically mediated methane oxidation at elevated temperatures, we set up 57 microcosms using soils from 14 Aotearoa-New Zealand geothermal fields and show that moderately thermophilic (>40°C) and thermophilic (>60°C) methane oxidation is common across the region. Methane oxidation was detected in 54% (n = 31) of the geothermal soil microcosms tested at temperatures up to 75°C (pH 1.5-8.1), with oxidation rates ranging from 0.5 to 17.4 μmol g-1 d-1 wet weight. The abundance of known aerobic methanotrophs (up to 60.7% Methylacidiphilum and 11.2% Methylothermus) and putative anaerobic methanotrophs (up to 76.7% Bathyarchaeota) provides some explanation for the rapid rates of methane oxidation observed in microcosms. However, not all methane oxidation was attributable to known taxa; in some methane-consuming microcosms we detected methanotroph taxa in conditions outside of their known temperature range for growth, and in other examples, we observed methane oxidation in the absence of known methanotrophs through 16S rRNA gene sequencing. Both of these observations suggest unidentified methane oxidizing microorganisms or undescribed methanotrophic syntrophic associations may also be present. Subsequent enrichment cultures from microcosms yielded communities not predicted by the original diversity studies and showed rates inconsistent with microcosms (≤24.5 μmol d-1), highlighting difficulties in culturing representative thermophilic methanotrophs. Finally, to determine the active methane oxidation processes, we attempted to elucidate metabolic pathways from two enrichment cultures actively oxidizing methane using metatranscriptomics. The most highly expressed genes in both enrichments (methane monooxygenases, methanol dehydrogenases and PqqA precursor peptides) were related to methanotrophs from Methylococcaceae, Methylocystaceae and Methylothermaceae. This is the first example of using metatranscriptomics to investigate methanotrophs from geothermal environments and gives insight into the metabolic pathways involved in thermophilic methanotrophy.

A Review on Hypothesized Metabolic Pathways on Europa and Enceladus: Space-Flight Detection Considerations

Enceladus and Europa, icy moons of Saturn and Jupiter, respectively, are believed to be habitable with liquid water oceans and therefore are of interest for future life detection missions and mission concepts. With the limited data from missions to these moons, many studies have sought to better constrain these conditions. With these constraints, researchers have, based on modeling and experimental studies, hypothesized a number of possible metabolisms that could exist on Europa and Enceladus if these worlds host life. The most often hypothesized metabolisms are methanogenesis for Enceladus and methane oxidation/sulfate reduction on Europa. Here, we outline, review, and compare the best estimated conditions of each moon's ocean. We then discuss the hypothetical metabolisms that have been suggested to be present on these moons, based on laboratory studies and Earth analogs. We also detail different detection methods that could be used to detect these hypothetical metabolic reactions and make recommendations for future research and considerations for future missions.

Metagenomics reveals the habitat specificity of biosynthetic potential of secondary metabolites in global food fermentations

BACKGROUND

Fermented foods are considered to be beneficial for human health. Secondary metabolites determined by biosynthetic gene clusters (BGCs) are precious bioactive compounds with various biological activities. However, the diversity and distribution of the biosynthetic potential of secondary metabolites in global food fermentations remain largely unknown. In this study, we performed a large-scale and comprehensive investigation for the BGCs in global food fermentations by metagenomics analysis.

RESULTS

We recovered 653 bacterial metagenome-assembled genomes (MAGs) from 367 metagenomic sequencing datasets covering 15 general food fermentation types worldwide. In total, 2334 secondary metabolite BGCs, including 1003 novel BGCs, were identified in these MAGs. Bacillaceae, Streptococcaceae, Streptomycetaceae, Brevibacteriaceae and Lactobacillaceae contained high abundances of novel BGCs (≥ 60 novel BGCs). Among 2334 BGCs, 1655 were habitat-specific, originating from habitat-specific species (80.54%) and habitat-specific genotypes within multi-habitat species (19.46%) in different food fermentation types. Biological activity analysis suggested that 183 BGC-producing secondary metabolites exhibited high probabilities of antibacterial activity (> 80%). These 183 BGCs were distributed across all 15 food fermentation types, and cheese fermentation contained the most BGC number.

CONCLUSIONS

This study demonstrates that food fermentation systems are an untapped reservoir of BGCs and bioactive secondary metabolites, and it provides novel insights into the potential human health benefits of fermented foods. Video Abstract.

Sulfur cycling connects microbiomes and biogeochemistry in deep-sea hydrothermal plumes

In globally distributed deep-sea hydrothermal vent plumes, microbiomes are shaped by the redox energy landscapes created by reduced hydrothermal vent fluids mixing with oxidized seawater. Plumes can disperse over thousands of kilometers and their characteristics are determined by geochemical sources from vents, e.g., hydrothermal inputs, nutrients, and trace metals. However, the impacts of plume biogeochemistry on the oceans are poorly constrained due to a lack of integrated understanding of microbiomes, population genetics, and geochemistry. Here, we use microbial genomes to understand links between biogeography, evolution, and metabolic connectivity, and elucidate their impacts on biogeochemical cycling in the deep sea. Using data from 36 diverse plume samples from seven ocean basins, we show that sulfur metabolism defines the core microbiome of plumes and drives metabolic connectivity in the microbial community. Sulfur-dominated geochemistry influences energy landscapes and promotes microbial growth, while other energy sources influence local energy landscapes. We further demonstrated the consistency of links among geochemistry, function, and taxonomy. Amongst all microbial metabolisms, sulfur transformations had the highest MW-score, a measure of metabolic connectivity in microbial communities. Additionally, plume microbial populations have low diversity, short migration history, and gene-specific sweep patterns after migrating from background seawater. Selected functions include nutrient uptake, aerobic oxidation, sulfur oxidation for higher energy yields, and stress responses for adaptation. Our findings provide the ecological and evolutionary bases of change in sulfur-driven microbial communities and their population genetics in adaptation to changing geochemical gradients in the oceans.

Baseline metagenome-assembled genome (MAG) data of Sikkim hot springs from Indian Himalayan geothermal belt (IHGB) showcasing its potential CAZymes, and sulfur-nitrogen metabolic activity

Here we present the construction and characterization of metagenome assembled genomes (MAGs) from two hot springs residing in the vicinity of Indian Himalayan Geothermal Belt (IHGB). A total of 78 and 7 taxonomic bins were obtained for Old Yume Samdong (OYS) and New Yume Samdong (NYS) hot springs respectively. After passing all the criteria only 21 and 4 MAGs were further studied based on the successful prediction of their 16 S rRNA. Various databases were used such as GTDB, Kaiju, EzTaxon, BLAST XY Plot and NCBI BLAST to get the taxonomic classification of various 16 S rRNA predicted MAGs. The bacterial genomes found were from both thermophilic and mesophilic bacteria among which Proteobacteria, Chloroflexi, Bacteroidetes and Firmicutes were the abundant phyla. However, in case of OYS, two genomes belonged to archaeal Methanobacterium and Methanocaldococcus. Functional characterization revealed the richness of CAZymes such as Glycosyl Transferase (GT) (56.7%), Glycoside Hydrolase (GH) (37.4%), Carbohydrate Esterase family (CE) (8.2%), and Polysaccharide Lyase (PL) (1.9%). There were negligible antibiotic resistance genes in the MAGs however, a significant heavy metal tolerance gene was found in the MAGs. Thus, it may be assumed that there is no coexistence of antibiotic and heavy metal resistance genes in these hot spring microbiomes. Since the selected hot springs possess good sulfur content thus, we also checked the presence of genes for sulfur and nitrogen metabolism. It was found that MAGs from both the hot springs possess significant number of genes related to sulfur and nitrogen metabolism.

Metagenome-based metabolic modelling predicts unique microbial interactions in deep-sea hydrothermal plume microbiomes

Deep-sea hydrothermal vents are abundant on the ocean floor and play important roles in ocean biogeochemistry. In vent ecosystems such as hydrothermal plumes, microorganisms rely on reduced chemicals and gases in hydrothermal fluids to fuel primary production and form diverse and complex microbial communities. However, microbial interactions that drive these complex microbiomes remain poorly understood. Here, we use microbiomes from the Guaymas Basin hydrothermal system in the Pacific Ocean to shed more light on the key species in these communities and their interactions. We built metabolic models from metagenomically assembled genomes (MAGs) and infer possible metabolic exchanges and horizontal gene transfer (HGT) events within the community. We highlight possible archaea-archaea and archaea-bacteria interactions and their contributions to the robustness of the community. Cellobiose, D-Mannose 1-phosphate, O2, CO2, and H2S were among the most exchanged metabolites. These interactions enhanced the metabolic capabilities of the community by exchange of metabolites that cannot be produced by any other community member. Archaea from the DPANN group stood out as key microbes, benefiting significantly as acceptors in the community. Overall, our study provides key insights into the microbial interactions that drive community structure and organisation in complex hydrothermal plume microbiomes.