Biology subjects

Herbold, C. W.

Publications and source records attributed to Herbold, C. W..

At least 19 recordsLinked to original sources

bioRxiv2026

Thermal stress disrupts microbial symbiosis and host activity in the model sponge Ianthella basta

Climate change is threatening coral reef ecosystems around the world, causing significant declines in reef organisms, including sponges. The health of sponges is intimately linked to their symbiosis with microorganisms, yet little is known about their integrated response to ocean warming. Here, we present a comprehensive view of the effect of elevated sea surface temperatures (SST) on the model sponge Ianthella basta. I. basta individuals were exposed to temperatures up to 32 {degrees}C, 2-3 {degrees}C above the mean annual maxima. Host gene expression profiles showed an initial response to heat stress after 2 days, and a decreased expression of genes involved in maintaining tissue integrity, pumping capacity, vitamin transport, and stable symbioses after 4 to 8 days. Congruently, heat stressed samples started to show tissue regression and a reduced abundance of the dominant symbionts after 4 days. A significant loss of the symbionts occurred after 8 days, together with a reduction in microbially driven nitrogen cycling and amino-acid transport and an introduction of opportunistic microbes, which could lead to nutrient imbalance and further destabilisation of the holobiont. Together, this work provides important insights into the avenues through which future SST can impact host-microbe interactions in coral reef sponges.

microbiology↗

bioRxiv2026

A Saccharimonadia epibiont interacts with the polyphosphate-accumulating bacterium Candidatus Phosphoribacter in wastewater treatment plants

Many Patescibacteria lineages are abundant in wastewater treatment plants, yet their interaction partners and ecological roles remain poorly understood. Here, we identify a specific association between a novel Saccharimonadia genus, Candidatus Lutisaccharimonas, and the widespread polyphosphate-accumulating organism (PAO) Candidatus Phosphoribacter. Fluorescence in situ hybridization revealed close physical proximity between the two taxa, supporting an epibiotic relationship. Correlated population dynamics, CRISPR spacer matches and evidence of horizontal gene transfer further corroborated this association. Comparative genomic analyses showed that Ca. Lutisaccharimonas has greater metabolic versatility than is typical of Patescibacteria, including complete pathways for de novo nucleotide biosynthesis and genes involved in amino acid metabolism. These metabolic features may shape its interactions with Ca. Phosphoribacter. Together, our findings identify a previously undescribed host association for Patescibacteria, expand current understanding of their metabolic potential, and suggest that the interactions between Saccharimonadia and PAOs may influence phosphorus removal in engineered ecosystems.

microbiology↗

bioRxiv2026

A Sample to Results Workflow for Compositional Analysis of Multiplexed Amplicon Sequencing Experiments

Microbial communities play key roles in the transformation and cycling of elements ranging from required macronutrients to toxic metalloids. Next-generation sequencing has been applied across multiple ecosystems to probe the interplay of microbial community structure and functional potential with respect to elemental cycling. Shotgun metagenomics collects marker gene sequences without amplification and is costly for large numbers of samples and deep coverage. Conversely, amplicon sequencing of taxonomic marker genes, e.g. 16S and 18S rRNA, is cost-effective for large numbers of samples, but provides limited functional insight. A middle ground between the two approaches is needed to analyze community structure and functional potential within a sample while remaining cost-effective with high throughput. To address this need, we developed a standardized workflow for multiplexed amplicon sequencing from sample collection through data analysis for diverse sample types, including freshwater, sediments, and soils, that produces data and publication-ready figures for multiple taxonomic and functional genes for carbon, nitrogen, phosphorus, sulfur, and arsenic cycling for each sample analyzed. The workflows utility was shown by analyzing 11 taxonomic and functional gene amplicons sequenced from 25 samples with high technical replicate similarity. The workflow is named CAMASE for Compositional Analysis of Multiplex Amplicon Sequencing Experiments. This proof-of-concept shows that CAMASE economically produces standard amplicon sequencing outputs (ASV/OTU counts and taxonomy, PCA, and relative abundance plots) for hundreds of amplicon by sample combinations and provides specific recommendations for implementation. GRAPHICAL ABSTRACT O_FIG O_LINKSMALLFIG WIDTH=200 HEIGHT=111 SRC="FIGDIR/small/741237v1_ufig1.gif" ALT="Figure 1"> View larger version (38K): org.highwire.dtl.DTLVardef@14c746corg.highwire.dtl.DTLVardef@6f9890org.highwire.dtl.DTLVardef@894038org.highwire.dtl.DTLVardef@d72b2a_HPS_FORMAT_FIGEXP M_FIG C_FIG Samples are collected in a preservative and material collected on filters prior to DNA extraction. Target gene amplicons are produced in parallel with internal barcodes enabling sequencing in a single run followed by compositional data analysis. All wet lab protocols, code markdowns, and templates for required metadata files are available at https://hansonlabgit.dbi.udel.edu/aprange/CAMASE. Created in BioRender. Bennett, A. (2026) https://BioRender.com/ymnojt0

microbiology↗

bioRxiv2026

The Celiac Microbiome Repository (CMR): A Curated Collection of Celiac Disease Gut Microbiome Sequencing Data

Celiac disease is an autoimmune condition where the gut microbiome is increasingly recognised as a key environmental factor. While high-throughput sequencing has led to a surge in celiac-related gut microbiome profiling data, these datasets remain fragmented, heterogeneous, and often lack the metadata required for large-scale integration into pooled, cross-cohort datasets. To address this, we developed the Celiac Microbiome Repository (CMR), a curated, open-access collection of celiac-related 16S rRNA gene and shotgun metagenomic sequencing datasets. We employed a systematic curation workflow to identify datasets across the NCBI Sequence Read Archive (SRA) and Scopus, followed by manual metadata extraction and direct author engagement. All 16S data was reprocessed through DADA2 and shotgun data through MetaPhlAn4 to facilitate comparison across studies. The CMR version 1.0 comprises 28 datasets containing 3,245 samples from 13 countries and 5 body sites. Our analysis reveals that while publicly available celiac microbiome samples have accumulated at a rate of approximately 140 per year, significant barriers to accessibility exist. Just 20 of 58 eligible datasets were found to have both raw data and essential metadata readily available within public archives. The repository features a dual-interface design, consisting of a GitHub backend for programmatic access and an R Shiny frontend for interactive data exploration. By providing this curated and harmonised resource, the CMR enables the research community to leverage public data for global meta-analyses and machine learning applications. Ultimately, this work provides the foundation needed to move beyond isolated, small-scale studies toward high-powered discoveries in celiac disease research. Database URLs: https://github.com/CeliacMicrobiomeRepo/celiac-repository | https://celiac.shinyapps.io/celiac-webapp

bioinformatics↗

bioRxiv2026

Micro16S: Universal Phylogenetic 16S rRNA Gene Representations for Deep Learning of the Microbiome

1Existing self-supervised microbiome models represent taxa as discrete, independent units restricted to fixed vocabularies, disregarding their evolutionary context. Here we present Micro16S, a deep learning approach that embeds 16S ribosomal RNA gene sequences into a continuous vector space according to phylogenetic relationships derived from the Genome Taxonomy Database. Using a combination of triplet and pair loss objectives, the model learns representations where spatial proximity reflects phylogenetic relatedness, while remaining largely invariant to the specific 16S rRNA region. Evaluations demonstrate taxonomically coherent clustering across most ranks and substantially improved region invariance compared to k-mer frequency baselines. A transformer pretrained on 50,418 unlabelled gut microbiome samples using these embeddings captured biologically meaningful community structure, though classical machine learning baselines outperformed Micro16S across six benchmark classification tasks, highlighting the limitations of the current system. These results establish the feasibility of phylogenetic embeddings for microbiome deep learning and identify mining algorithm design and class imbalance as primary targets for future improvement.

bioinformatics↗

bioRxiv2025

Associations between gut microbiota and personality traits: insights from a captive common marmoset (Callithrix jacchus) colony

Recent studies have suggested the link between inter-individual behavioural variation (i.e., animal personality) and gut microbiota. Non-human primates living under controlled conditions are valuable models to investigate diet-independent microbiome-host interactions. In this study, we investigated links between specific gut microbiota members and personality traits, as well as group membership, sex, age class, breeding status and relatedness of 26 captive common marmosets (Callithrix jacchus), maintained under the same diet and housing conditions. Personality was assessed using an established testing battery in repeated tests. Then, we collected a total of 225 fecal samples during the summers of 2017 and 2019 from five marmoset social groups for 16S rRNA gene amplicon sequencing. Within-individual microbiota variance was smaller than that between group members. Group members also exhibited more similar gut microbiota than individuals from different groups in each sampling year. Beta diversity of the gut microbiota was linked with personality traits, age class, sex, and breeding status, but not with genetic relatedness. We identified specific bacterial taxa associated with personality traits. In particular, members of the sulfite-reducing genera Desulfovibrio were enriched in more avoidant marmosets. Amplicon sequencing of the dissimilatory sulfite reductase gene dsrB confirmed this pattern, yet additionally revealed an unknown uncultured bacterium that was the predominant sulfite-reducing bacterium in the fecal samples and was linked to more explorative individuals. These findings highlight specific association patterns between selected microbial taxa and personality traits in captive common marmosets. ImportanceThis study provides valuable insights into the intricate relationship between gut microbiota and host personality traits, using captive common marmosets as a model. By controlling for diet and housing conditions, it probes key host factors such as personality, age, sex, and social group membership, offering a robust framework for understanding microbiome-host interactions. The discovery of specific microbial taxa associated with personality traits, particularly the enrichment of sulfite-reducing genera in more avoidant individuals, underscores the potential role of the gut microbiome in shaping or reflecting personality. These findings advance our understanding of microbiome-host dynamics and pave the way for future research on the mechanistic links between behavior and gut microbiota in other animal models and across broader ecological contexts.

microbiology↗

bioRxiv2024

Antarctic geothermal soils exhibit an absence of regional habitat generalist microorganisms

Active geothermal systems are relatively rare in Antarctica and represent metaphorical islands ideal to study microbial dispersal. In this study, we tested the macroecological concept that high dispersal rates result in communities being dominated by either habitat generalists or specialists by investigating the microbial communities on four geographically separated geothermal sites on three Antarctic volcanoes (Mts. Erebus, Melbourne and Rittman). We found that the microbial communities at higher temperature (max 65{square}) sites (Tramway Ridge on Erebus and Rittmann) were unique from each other and were dominated by a variety of novel Archaea from class Nitrososphaeria, while lower temperature (max 50{square}) sites (Western Crater on Erebus and Melbourne) had characteristically mesophilic communities (Planctomycetes, Acidobacteriota, etc) that were highly similar. We found that 97% of the detected microbial taxa were regional habitat specialists, with no generalists, with community assembly driven by high dispersal rates and drift (25 and 30% of community assembly, respectively), not environmental selection. Our results indicate that for microbial communities experiencing high dispersal rates between isolated communities, habitat specialists may tend to out-compete habitat generalists.

microbiology↗

bioRxiv2024

Geothermal ecosystems on Mt. Erebus, Antarctica, support diverse and taxonomically novel biota

Mt. Erebus, Antarctica, is the southernmost active volcano in the world and harbors a diverse and geochemically unique array of geothermal ecosystems including Subglacial and Exposed features, surrounded by a vast desert of ice and snow. Previous studies, although limited in scope, have highlighted the unique and potentially endemic biota present on Mt. Erebus. In this study, we provide a systematic biodiversity study across all domains of life and all types of geothermal features present on Mt. Erebus. We present physicochemical and biological data from 39 Exposed samples and 9 Subglacial samples from Mt. Erebus. The taxonomic novelty of prokaryotes and fungi found supports past hypotheses of high endemism among the biota of Mt. Erebus; in particular, the large number of taxonomically divergent fungal sequences was surprising. We found that different site types had unique physicochemistry and biota; in particular, Exposed sites were significantly warmer than Subglacial sites (median: 40 vs 10 for Exposed and Subglacial, respectively) and tended to have greater abundances of photosynthetic organisms (Cyanobacteria and Chlorophyta). Subglacial sites were characterized by a greater abundance of prokaryotes from the phylum Actinobacteriota, correlated with the greater concentrations of Ca, Mg, and Sr present. Additionally, we found that Tramway Ridge differed from other Exposed sites as well as all Subglacial sites in physicochemistry (significantly greater conductivity, water content, total carbon, and total nitrogen levels) and biota (greater relative abundances of order Nitrososphaeria and phylum Bacteroidota). In this study, we provide a blueprint for future work aimed at better understanding the novel biota of Mt. Erebus.

microbiology↗

bioRxiv2024

Genome-wide sweeps create fundamental ecological units in the human gut microbiome

The human gut microbiome is shaped by diverse selective forces originating from the host and associated environmental factors, and in turn profoundly influences health and disease. While the association of microbial lineages with various conditions has been shown at different levels of phylogenetic differentiation, it remains poorly understood to what extent unifying adaptive mechanisms sort microbial lineages into ecologically differentiated populations. Here we show that a pervasive mechanism differentiating bacteria in the microbiome are genome-wide selective sweeps, leading to population structure akin to global epidemics across geographically and ethnically diverse human populations. Such sweeps arise when an adaptation allows a clone to outcompete others within its niche followed by re-diversification, and manifest as clusters of closely related genomes on long branches in phylogenetic trees. This structure is revealed by excluding recombination events that mask the clonal descent of the genomes, and we find that genome-wide sweeps originate under a wide regime of recombination rates in at least 66 taxa from 25 bacterial families. Estimated ages of divergence suggest sweep clusters can spread globally within decades, and this process has occurred repeatedly throughout human history. We show, as an example, that the ecological differentiation of sweep clusters forms populations highly associated with age and colorectal cancer. Our analysis elucidates an evolutionary mechanism for the observation of stably inherited strains with differential associations and provides a theoretical foundation for analyzing adaptation among co-occurring microbial populations.

microbiology↗

bioRxiv2023

Global abundance patterns, diversity, and ecology of Patescibacteria in wastewater treatment plants

BackgroundMicroorganisms are responsible for nutrient removal and resource recovery in wastewater treatment plants (WWTPs), and their diversity is often studied by 16S rRNA gene amplicon sequencing. However, this approach underestimates the abundance and diversity of Patescibacteria due to the low coverage of commonly used PCR primers for this highly divergent bacterial phylum. Therefore, our current understanding of the global diversity, distribution, and ecological role of Patescibacteria in WWTPs is very incomplete. This is particularly relevant as Patescibacteria are considered to be associated with microbial host cells and can therefore influence the abundance and temporal variability of other microbial groups that are important for WWTP functioning. ResultsHere, we evaluated the in silico coverage of widely used 16S rRNA gene-targeted primer pairs and redesigned a primer pair targeting the V4 region of bacterial and archaeal 16S rRNA genes to expand its coverage for Patescibacteria. We then experimentally evaluated and compared the performance of the original and modified V4-targeted primers on 565 WWTP samples from the MiDAS global sample collection. Using the modified primer pair, the percentage of ASVs classified as Patescibacteria increased from 5.9% to 23.8%, and the number of detected patescibacterial genera increased from 560 to 1,576, while the detected diversity of the remaining microbial community remained similar. Due to this significantly improved coverage of Patescibacteria, we identified 23 core genera of Patescibacteria in WWTPs and described the global distribution pattern of these unusual microbes in these systems. Finally, correlation network analysis revealed potential host organisms that might be associated with Patescibacteria in WWTPs. Interestingly, strong indications were found for an association between Patescibacteria of the Saccharimonadia and globally abundant polyphosphate-accumulating organisms of the genus Ca. Phosporibacter. ConclusionsOur study (i) provides an improved 16S rRNA gene V4 region-targeted amplicon primer pair inclusive of Patescibacteria with little impact on the detection of other taxa, (ii) reveals the diversity and distribution patterns of Patescibacteria in WWTPs on a global scale, and (iii) provides new insights into the ecological role and potential hosts of Patescibacteria in WWTPs.

ecology↗

bioRxiv2022

Taurine as a key intermediate for host-symbiont interaction in the tropical sponge Ianthella basta

Marine sponges are critical components of marine benthic fauna assemblages where their filter-feeding and reef-building capabilities provide bentho-pelagic coupling and crucial habitat. As potentially the oldest representation of a metazoan-microbe symbiosis, they also harbor dense, diverse, and species-specific communities of microbes, which are increasingly recognized for their contributions to dissolved organic matter (DOM) processing. Recent omics-based studies of marine sponge microbiomes have proposed numerous pathways of dissolved metabolite exchange between the host and symbionts within the context of the surrounding environment, but few studies have sought to experimentally interrogate these pathways. By using a combination of metaproteogenomics and laboratory incubations coupled with isotope-based functional assays, we showed that the dominant gammaproteobacterial symbiont Candidatus Taurinisymbion ianthellae residing in the marine sponge, Ianthella basta, expresses a pathway for the import and dissimilation of taurine, a ubiquitously occurring sulfonate metabolite in marine sponges. Candidatus Taurinisymbion ianthellae incorporates taurine-derived carbon and nitrogen while, at the same time, oxidizing the dissimilated sulfite into sulfate for export. Furthermore, we found that taurine-derived ammonia is exported by the symbiont for immediate oxidation by the dominant ammonia-oxidizing thaumarchaeal symbiont Candidatus Nitrosospongia ianthellae. Metaproteogenomic analyses also indicate that Candidatus Taurinisymbion ianthellae likely imports DMSP and possesses both pathways for DMSP demethylation and cleavage, enabling it to use this compound as a carbon and sulfur source for biomass, as well as for energy conservation. These results highlight the important role of biogenic sulfur compounds in the interplay between Ianthella basta and its microbial symbionts.

microbiology↗

bioRxiv2021

Ammonia-oxidizing archaea possess a wide range of cellular ammonia affinities

Nitrification, the oxidation of ammonia to nitrate, is an essential process in the biogeochemical nitrogen cycle. The first step of nitrification, ammonia oxidation, is performed by three, often co- occurring guilds of chemolithoautotrophs: ammonia-oxidizing bacteria (AOB), archaea (AOA), and complete ammonia oxidizers (comammox). Substrate kinetics are considered to be a major niche-differentiating factor between these guilds, but few AOA strains have been kinetically characterized. Here, the ammonia oxidation kinetic properties of 12 AOA representing all major phylogenetic lineages were determined using microrespirometry. Members of the genus Nitrosocosmicus have the lowest substrate affinity of any characterized AOA, which are similar to previously determined affinities of AOB. This contrasts previous assumptions that all AOA possess much higher substrate affinities than their comammox or AOB counterparts. The substrate affinity of ammonia oxidizers correlated with their cell surface area to volume ratios. In addition, kinetic measurements across a range of pH values strongly supports the hypothesis that - like for AOB - ammonia and not ammonium is the substrate for the ammonia monooxygenase enzyme of AOA and comammox. Together, these data will facilitate predictions and interpretation of ammonia oxidizer community structures and provide a robust basis for establishing testable hypotheses on competition between AOB, AOA, and comammox.

microbiology↗

bioRxiv2020

A novel oxidase from Alcaligenes sp. HO-1 oxidizes hydroxylamine to N2

Hydroxylamine is a key intermediate of microbial ammonia oxidation and plays an important role in the biogeochemical cycling of N-compounds. Hydroxylamine is oxidized to NO or N2O by hydroxylamine oxidases or cytochrome P460 from heterotrophic or autotrophic bacteria, but its enzymatic oxidation to N2 has not yet been observed. Here, we report on the discovery of a novel oxidase that converts hydroxylamine to N2 from the newly isolated heterotrophic nitrifier Alcaligenes strain HO-1. Strain HO-1 accumulated hydroxylamine and produced N2 from ammonia oxidation. Using transcriptome analysis and heterologous expression via fosmid library screening, we identified three genes (dnfABC) of strain HO-1 that enabled E. coli cells not only to produce hydroxylamine from 15N-labelled ammonium but also to further convert it to 15N2. The three genes were individually cloned and expressed, and their translational products DnfA, DnfB, and DnfC were purified. In vitro DnfA bound to hydroxylamine and catalyzed the conversion of hydroxylamine to N2 in the presence of FAD, NADH and O2. Thus, DnfA was identified as a novel hydroxylamine oxidase and catalyzed a previously unknown N-N bond forming reaction with a yet-to-be discovered mechanism. DnfA homologs were detected in different bacterial groups, suggesting that hydroxylamine oxidation to nitrogen might occur in additional microbial taxa.

microbiology↗

bioRxiv2020

Genomic and kinetic analysis of novel Nitrospinae enriched by cell sorting

Chemolithoautotrophic nitrite-oxidizing bacteria (NOB) are key players in global nitrogen and carbon cycling. Members of the phylum Nitrospinae are the most abundant, known NOB in the oceans. To date, only two closely affiliated Nitrospinae species have been isolated, which are only distantly related to the environmentally abundant uncultured Nitrospinae clades. Here, we applied live cell sorting, activity screening, and subcultivation on marine nitrite-oxidizing enrichments to obtain novel marine Nitrospinae. Two binary cultures were obtained, each containing one Nitrospinae strain and one alphaproteobacterial heterotroph. The Nitrospinae strains represent two new genera, and one strain is more closely related to environmentally abundant Nitrospinae than previously cultured NOB. With an apparent half-saturation constant of 8.7{+/-}2.5 {micro}M, this strain has the highest affinity for nitrite among characterized marine NOB, while the other strain (16.2{+/-}1.6 {micro}M) and Nitrospina gracilis (20.1{+/-}2.1 {micro}M) displayed slightly lower nitrite affinities. The new strains and N. gracilis share core metabolic pathways for nitrite oxidation and CO2 fixation but differ remarkably in their genomic repertoires of terminal oxidases, use of organic N sources, alternative energy metabolisms, osmotic stress and phage defense. The new strains, tentatively named "Candidatus Nitrohelix vancouverensis" and "Candidatus Nitronauta litoralis", shed light on the niche differentiation and potential ecological roles of Nitrospinae.

microbiology↗

bioRxiv2020

Exploring the upper pH limits of nitrite oxidation: diversity, ecophysiology, and adaptive traits of haloalkalitolerant Nitrospira

Nitrite-oxidizing bacteria of the genus Nitrospira are key players of the biogeochemical nitrogen cycle. However, little is known about their occurrence and survival strategies in extreme pH environments. Here, we report on the discovery of physiologically versatile, haloalkalitolerant Nitrospira that drive nitrite oxidation at exceptionally high pH. Nitrospira distribution, diversity, and ecophysiology were studied in hypo- and subsaline (1.3-12.8 g salt/l), highly alkaline (pH 8.9-10.3) lakes by amplicon sequencing, metagenomics, and cultivation-based approaches. Surprisingly, not only were Nitrospira populations detected, but they were also considerably diverse with presence of members of Nitrospira lineages I, II and IV. Furthermore, the ability of Nitrospira enrichment cultures to oxidize nitrite at neutral to highly alkaline pH of 10.5 was demonstrated. Metagenomic analysis of a newly enriched Nitrospira lineage IV species, "Candidatus Nitrospira alkalitolerans", revealed numerous adaptive features of this organism to its extreme environment. Among them were a sodium-dependent N-type ATPase and NADH:quinone oxidoreductase next to the proton-driven forms usually found in Nitrospira. Other functions aid in pH and cation homeostasis and osmotic stress defense. "Ca. Nitrospira alkalitolerans" also possesses group 2a and 3b [NiFe] hydrogenases, suggesting it can use hydrogen as alternative energy source. These results reveal how Nitrospira cope with strongly fluctuating pH and salinity conditions and expand our knowledge of nitrogen cycling in extreme habitats.

microbiology↗

bioRxiv2019

Glacial runoff promotes deep burial of sulfur cycling-associated microorganisms in marine sediments

Marine fjords with active glacier outlets are hot spots for organic matter burial in the sediments and subsequent microbial mineralization, and will be increasingly important as climate warming causes more rapid glacial melt. Here, we investigated controls on microbial community assembly in sub-arctic glacier-influenced (GI) and non-glacier-influenced (NGI) marine sediments in the Godth[a]bsfjord region, south-western Greenland. We used a correlative approach integrating 16S rRNA gene and dissimilatory sulfite reductase (dsrB) amplicon sequence data over six meters of depth with biogeochemistry, sulfur-cycling activities, and sediment ages. GI sediments were characterized by comparably high sedimentation rates and had young sediment ages of <500 years even at 6 m sediment depth. In contrast, NGI stations reached ages of approximately 10,000 years at these depths. Sediment age-depth relationships, sulfate reduction rates, and C/N ratios were strongly correlated with differences in microbial community composition between GI and NGI sediments, indicating that age and diagenetic state were key drivers of microbial community assembly in subsurface sediments. Similar bacterial and archaeal communities were present in the surface sediments of all stations, whereas only in GI sediments were many surface taxa also abundant through the whole sediment core. The relative abundance of these taxa, including diverse Desulfobacteraceae members, correlated positively with sulfate reduction rates, indicating their active contributions to sulfur-cycling processes. In contrast, other surface community members, such as Desulfatiglans, Atribacteria and Chloroflexi, survived the slow sediment burial at NGI stations and dominated in the deepest sediment layers. These taxa are typical for the energy-limited marine deep biosphere and their relative abundances correlated positively with sediment age. In conclusion, our data suggests that high rates of sediment accumulation caused by glacier runoff and associated changes in biogeochemistry, promote persistence of sulfur-cycling activity and burial of a larger fraction of the surface microbial community into the deep subsurface.\n\nContribution to the Field StatementIn most coastal marine sediments organic matter turnover and total energy flux are highest at the surface and decrease significantly with increasing sediment depth, causing depth-dependent changes in the microbial community composition. Glacial runoff in arctic and subarctic fjords alters the composition of the microbial community at the surface, mainly due to different availabilities of organic matter and metals. Here we show that glacial runoff also modifies microbial community assembly with sediment depth. Sediment age was a key driver of microbial community composition in six-meter-long marine sediment cores from the Godth[a]bsfjord region, south-western Greenland. High sedimentation rates at glacier-influenced sediment stations enabled a complex community of sulfur-cycling-associated microorganisms to continuously thrive at high relative abundances from the surface into the sediment subsurface. These communities consisted of putative fermenters, sulfate reducers and sulfur oxidizers, which likely depended on high metal concentrations in the relatively young, glacier-influenced sediments. In non-glacier-influenced sediments with lower sedimentation rates, these sulfur-cycling-associated microorganisms were only present near the surface. With increasing sediment depth these surface microorganisms were largely replaced by other surface microorganisms that positively correlated with sediment age and belong to known taxa of the energy-limited, marine deep biosphere.

microbiology↗

bioRxiv2019

Characterization of a thaumarchaeal symbiont that drives incomplete nitrification in the tropical sponge Ianthella basta

Marine sponges represent one of the few eukaryotic groups that frequently harbor symbiotic members of the Thaumarchaeota, which are important chemoautotrophic ammonia-oxidizers in many environments. However, in most studies, direct demonstration of ammonia-oxidation by these archaea within sponges is lacking, and little is known about sponge-specific adaptations of ammonia-oxidizing archaea (AOA). Here, we characterized the thaumarchaeal symbiont of the marine sponge Ianthella basta using metaproteogenomics, fluorescence in situ hybridization, qPCR and isotope-based functional assays. "Candidatus Nitrosospongia bastadiensis" is only distantly related to cultured AOA. It is an abundant symbiont that is solely responsible for nitrite formation from ammonia in I. basta that surprisingly does not harbor nitrite-oxidizing microbes. Furthermore, this AOA is equipped with an expanded set of extracellular subtilisin-like proteases, a metalloprotease unique among archaea, as well as a putative branched-chain amino acid ABC transporter. This repertoire is strongly indicative of a mixotrophic lifestyle and is (with slight variations) also found in other sponge-associated, but not in free-living AOA. We predict that this feature as well as an expanded and unique set of secreted serpins (protease inhibitors), a unique array of eukaryotic-like proteins, and a DNA-phosporothioation system, represent important adaptations of AOA to life within these ancient filter-feeding animals. Originality-Significance StatementMany marine sponges harbor symbiotic members of the Thaumarchaeota, but there is generally only indirect evidence available about their functional role within these filter-feeding animals. Furthermore, the specific adaptations of thaumarchaeal symbionts to their sponge hosts are incompletely understood. In this study, we thoroughly characterized a thaumarchaeal symbiont residing in the reef sponge Ianthella basta and demonstrate by using a combination of molecular tools and isotope techniques, that it is the only ammonia-oxidizer in its host. In contrast to other sponges, I. basta does not contain nitrite-oxidizing microbes and thus excretes considerable amounts of nitrite. Furthermore, using metagenomics and metaproteomics we reveal important adaptations of this symbiont, that represents a new genus within the Thaumarchaeota, and conclude that it most likely lives as a mixotroph in its sponge host.

microbiology↗

bioRxiv2019

DNA-foraging bacteria in the seafloor

Extracellular DNA is a major macromolecule in global element cycles, and is a particularly crucial phosphorus as well as nitrogen and carbon source for microorganisms in the seafloor. Nevertheless, the identities, ecophysiology and genetic features of key DNA-foraging microorganisms in marine sediments are completely unknown. Here we combined microcosm experiments, stable isotope probing and genome-centric metagenomics to study microbial catabolism of DNA and its sub-components in anoxic marine sediments. 13C-DNA added to sediment microcosms was degraded within ten days and mineralised to 13CO2. Stable isotope probing showed that diverse Candidatus Izemoplasma, Lutibacter, Shewanella, Fusibacteraceae and Nitrincolaceae incorporated DNA-derived 13C-carbon. Genomes representative of the 13C-labelled taxa were recovered and all encoded enzymatic repertoires for catabolism of DNA. Comparative genomics indicated that DNA can be digested by diverse members of the order Candidatus Izemoplasmatales (former Tenericutes), which appear to be specialised DNA-degraders that encode multiple extracellular nucleases. Fusibacteraceae lacked genes for extracellular nucleases but utilised various individual purine- and pyrimidine-based molecules, suggesting they cheated on liberated sub-components of DNA. Close relatives of the DNA-degrading taxa are globally distributed in marine sediments, suggesting that these poorly understood taxa contribute widely to the key ecosystem function of degrading and recycling DNA in the seabed.

microbiology↗