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  1. Abstract

    High-temperature geothermal springs host simplified microbial communities; however, the activities of individual microorganisms and their roles in the carbon cycle in nature are not well understood. Here, quantitative stable isotope probing (qSIP) was used to track the assimilation of 13C-acetate and 13C-aspartate into DNA in 74 °C sediments in Gongxiaoshe Hot Spring, Tengchong, China. This revealed a community-wide preference for aspartate and a tight coupling between aspartate incorporation into DNA and the proliferation of aspartate utilizers during labeling. Both 13C incorporation into DNA and changes in the abundance of taxa during incubations indicated strong resource partitioning and a significant phylogenetic signal for aspartate incorporation. Of the active amplicon sequence variants (ASVs) identified by qSIP, most could be matched with genomes from Gongxiaoshe Hot Spring or nearby springs with an average nucleotide similarity of 99.4%. Genomes corresponding to aspartate primary utilizers were smaller, near-universally encoded polar amino acid ABC transporters, and had codon preferences indicative of faster growth rates. The most active ASVs assimilating both substrates were not abundant, suggesting an important role for the rare biosphere in the community response to organic carbon addition. The broad incorporation of aspartate into DNA over acetate by the hot spring community may reflect dynamic cycling of cell lysis products in situ or substrates delivered during monsoon rains and may reflect N limitation.

     
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  2. Free, publicly-accessible full text available March 1, 2024
  3. Archaeal membrane lipids are widely used for paleotemperature reconstructions, yet these molecular fossils also bear rich information about ecology and evolution of marine ammonia-oxidizing archaea (AOA). Here we identified thermal and nonthermal behaviors of archaeal glycerol dialkyl glycerol tetraethers (GDGTs) by comparing the GDGT-based temperature index (TEX 86 ) to the ratio of GDGTs with two and three cyclopentane rings (GDGT-2/GDGT-3). Thermal-dependent biosynthesis should increase TEX 86 and decrease GDGT-2/GDGT-3 when the ambient temperature increases. This presumed temperature-dependent (PTD) trend is observed in GDGTs derived from cultures of thermophilic and mesophilic AOA. The distribution of GDGTs in suspended particulate matter (SPM) and sediments collected from above the pycnocline—shallow water samples—also follows the PTD trend. These similar GDGT distributions between AOA cultures and shallow water environmental samples reflect shallow ecotypes of marine AOA. While there are currently no cultures of deep AOA clades, GDGTs derived from deep water SPM and marine sediment samples exhibit nonthermal behavior deviating from the PTD trend. The presence of deep AOA increases the GDGT-2/GDGT-3 ratio and distorts the temperature-controlled correlation between GDGT-2/GDGT-3 and TEX 86 . We then used Gaussian mixture models to statistically characterize these diagnostic patterns of modern AOA ecology from paleo-GDGT records to infer the evolution of marine AOA from the Mid-Mesozoic to the present. Long-term GDGT-2/GDGT-3 trends suggest a suppression of today’s deep water marine AOA during the Mesozoic–early Cenozoic greenhouse climates. Our analysis provides invaluable insights into the evolutionary timeline and the expansion of AOA niches associated with major oceanographic and climate changes. 
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  4. Free, publicly-accessible full text available May 1, 2024
  5. Abstract

    A few members of the bacterial genusThermushave been shown to be incomplete denitrifiers, terminating with nitrite (NO2) or nitrous oxide (N2O). However, the denitrification abilities of the genus as a whole remain poorly characterized. Here, we describe diverse denitrification phenotypes and genotypes of a collection of 24 strains representing ten species, all isolated from a variety of geothermal systems in China. Confirmed terminal products of nitrate reduction were nitrite or N2O, while nitric oxide (NO) was inferred as the terminal product in some strains. Most strains produced N2O; complete denitrification was not observed. Denitrification phenotypes were largely consistent with the presence of denitrification genes, and strains of the same species often had the same denitrification phenotypes and largely syntenous denitrification gene clusters. Genes fornirSandnirKcoexisted in threeThermus brockianusand threeThermus oshimaigenomes, which is a unique hallmark of some denitrifyingThermusstrains and may be ecologically important. These results show that incomplete denitrification phenotypes are prominent, but variable, within and betweenThermusspecies. The incomplete denitrification phenotypes described here suggestThermusspecies may play important roles in consortial denitrification in high-temperature terrestrial biotopes where sufficient supply of oxidized inorganic nitrogen exists.

     
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  6. Abstract Background

    CandidatusNanohaloarchaeota, an archaeal phylum within the DPANN superphylum, is characterized by limited metabolic capabilities and limited phylogenetic diversity and until recently has been considered to exclusively inhabit hypersaline environments due to an obligate association withHalobacteria. Aside from hypersaline environments,Ca.Nanohaloarchaeota can also have been discovered from deep-subsurface marine sediments.

    Results

    Three metagenome-assembled genomes (MAGs) representing a new order within theCa.Nanohaloarchaeota were reconstructed from a stratified salt crust and proposed to represent a novel order,Nucleotidisoterales. Genomic features reveal them to be anaerobes capable of catabolizing nucleotides by coupling nucleotide salvage pathways with lower glycolysis to yield free energy. Comparative genomics demonstrated that these and otherCa.Nanohaloarchaeota inhabiting saline habitats use a “salt-in” strategy to maintain osmotic pressure based on the high proportion of acidic amino acids. In contrast, previously describedCa.Nanohaloarchaeota MAGs from geothermal environments were enriched with basic amino acids to counter heat stress. Evolutionary history reconstruction revealed that functional differentiation of energy conservation strategies drove diversification withinCa.Nanohaloarchaeota, further leading to shifts in the catabolic strategy from nucleotide degradation within deeper lineages to polysaccharide degradation within shallow lineages.

    Conclusions

    This study provides deeper insight into the ecological functions and evolution of the expanded phylumCa.Nanohaloarchaeota and further advances our understanding on the functional and genetic associations between potential symbionts and hosts.

     
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  7. Abstract

    Candidate bacterial phylum Omnitrophota has not been isolated and is poorly understood. We analysed 72 newly sequenced and 349 existing Omnitrophota genomes representing 6 classes and 276 species, along with Earth Microbiome Project data to evaluate habitat, metabolic traits and lifestyles. We applied fluorescence-activated cell sorting and differential size filtration, and showed that most Omnitrophota are ultra-small (~0.2 μm) cells that are found in water, sediments and soils. Omnitrophota genomes in 6 classes are reduced, but maintain major biosynthetic and energy conservation pathways, including acetogenesis (with or without the Wood-Ljungdahl pathway) and diverse respirations. At least 64% of Omnitrophota genomes encode gene clusters typical of bacterial symbionts, suggesting host-associated lifestyles. We repurposed quantitative stable-isotope probing data from soils dominated by andesite, basalt or granite weathering and identified 3 families with high isotope uptake consistent with obligate bacterial predators. We propose that most Omnitrophota inhabit various ecosystems as predators or parasites.

     
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  8. Abstract

    Although the phylum Chloroflexota is ubiquitous, its biology and evolution are poorly understood due to limited cultivability. Here, we isolated two motile, thermophilic bacteria from hot spring sediments belonging to the genus Tepidiforma and class Dehalococcoidia within the phylum Chloroflexota. A combination of cryo-electron tomography, exometabolomics, and cultivation experiments using stable isotopes of carbon revealed three unusual traits: flagellar motility, a peptidoglycan-containing cell envelope, and heterotrophic activity on aromatics and plant-associated compounds. Outside of this genus, flagellar motility has not been observed in Chloroflexota, and peptidoglycan-containing cell envelopes have not been described in Dehalococcoidia. Although these traits are unusual among cultivated Chloroflexota and Dehalococcoidia, ancestral character state reconstructions showed flagellar motility and peptidoglycan-containing cell envelopes were ancestral within the Dehalococcoidia, and subsequently lost prior to a major adaptive radiation of Dehalococcoidia into marine environments. However, despite the predominantly vertical evolutionary histories of flagellar motility and peptidoglycan biosynthesis, the evolution of enzymes for degradation of aromatics and plant-associated compounds was predominantly horizontal and complex. Together, the presence of these unusual traits in Dehalococcoidia and their evolutionary histories raise new questions about the timing and selective forces driving their successful niche expansion into global oceans.

     
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  9. Abstract Trace metals have been an important ingredient for life throughout Earth’s history. Here, we describe the genome-guided cultivation of a member of the elusive archaeal lineage Caldarchaeales (syn. Aigarchaeota ), Wolframiiraptor gerlachensis , and its growth dependence on tungsten. A metagenome-assembled genome (MAG) of W. gerlachensis encodes putative tungsten membrane transport systems, as well as pathways for anaerobic oxidation of sugars probably mediated by tungsten-dependent ferredoxin oxidoreductases that are expressed during growth. Catalyzed reporter deposition-fluorescence in-situ hybridization (CARD-FISH) and nanoscale secondary ion mass spectrometry (nanoSIMS) show that W. gerlachensis preferentially assimilates xylose. Phylogenetic analyses of 78 high-quality Wolframiiraptoraceae MAGs from terrestrial and marine hydrothermal systems suggest that tungsten-associated enzymes were present in the last common ancestor of extant Wolframiiraptoraceae . Our observations imply a crucial role for tungsten-dependent metabolism in the origin and evolution of this lineage, and hint at a relic metabolic dependence on this trace metal in early anaerobic thermophiles. 
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  10. Abstract

    Despite the ecological significance of desert springs, little is known about relationships between spring hydrogeochemistry and ecology, particularly over multiple trophic levels. Here, we surveyed microbial communities (bacteria and archaea) and benthic macroinvertebrate (BMI) communities in springs that recharge through granitoid bedrock in Owens Valley, CA, to determine whether subtle geochemical differences imparted by metamorphosed roof pendant weathering in the source area affect spring ecosystems. Relative to other springs, roof‐pendant‐recharged springs were characterized by elevated (1) Ca2+/Na+, Ca2+/Mg2+, and divalent/monovalent cation ratios, (2) relative abundance of taxa inferred to be benthic aerobes and prosthecate/stalked bacteria, and (3) abundance and diversity of shredder and collector gatherer BMIs. These BMI feeding groups graze on biofilm communities and stimulate bacterial degradation of particulate organic matter, consistent with extensive bacteria–BMI connections in co‐occurrence networks in these springs. Springs not impacted by roof pendants were instead enriched with taxa inferred to be anaerobes, chemolithotrophs, and low‐diversity BMI communities with poor bacteria–BMI network connectivity. We speculate that excess Ca2+derived from roof pendant weathering plays a key role in biofilm formation on coarse granite substrates, with subsequent trophic interactions between benthic microbial biofilms and diverse BMI shredders/collector gatherers.

     
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