Durusdinium trenchii is a unicellular dinoflagellate in the family Symbiodiniaceae, a diverse group of photosynthetic microalgae known for forming symbiotic relationships with cnidarians and other reef organisms. Notably, this species displays exceptional tolerance to heat stress, enabling it to persist within the coral gastrodermis and often dominate symbiont communities under elevated temperatures. D. trenchii can confer increased thermal tolerance and reduced bleaching susceptibility to corals, though frequently with trade-offs in host growth and calcification. Its resilience has been linked to genome duplication, photoprotective mechanisms and characteristic lipid profiles. Its unique molecular traits, host generalist nature, ecological flexibility and increasing prevalence in warming oceans underscore the importance of this microbe in coral reef responses to climate change.

Corals represent a complex assemblage consisting of a host cnidarian, symbiotic dinoflagellate microalgae, and associated microbiomes and viromes, collectively called the coral holobiont. Corals are foundational to tropical reefs, yet their global decline due to climate change and other stressors creates an uncertain future for this valuable ecosystem. Metabolomics is a powerful means to unravel biochemical interactions within the holobiont that underpin coral resilience and adaptation. However, the remote nature of reefs and the analytical demands of this technique often limit its application. Untargeted metabolomics presents analytical challenges that are amplified in complex samples like corals, such as identifying the biological source of metabolites. Here, we evaluate how different sample fixation methods and time delays before storage, unavoidable in field contexts, affect coral metabolome profiles. We further present a framework for mapping metabolites in holobiont samples to their coral host and algal symbiont origins and introduce a spectral library to improve and automate annotation of coral lipids. Additionally, we demonstrate how single samples can be used concurrently for metabolomics, DNA amplification, and proteomics. Together, our study provides a streamlined, field-adaptable workflow for coral metabolomics that enables larger-scale studies and broader adoption of metabolomics in coral reef research and conservation. ### Competing Interest Statement The authors have declared no competing interest. Michigan State University Climate Change Research Support Program U.S. National Science Foundation, https://ror.org/021nxhr62, NSF-ORCC-2307516 Defense Advanced Research Projects Agency, DARPA-HR001122C0134

Gut dysbiosis compromises cancer immunosurveillance by downregulating ileal mucosal addressin cell adhesion molecule 1 (MAdCAM-1), but the metabolic landscape associated with gut dysbiosis remains elusive. Here, we show that antibiotics (ABX) or ABX-associated Enterocloster species lead to the loss of secondary bile acids (BAs) including deoxycholic acid (DCA) and the accumulation of tauro-conjugated primary BAs (tauro-chenodeoxycholic acid [TCDCA] and tauro-β-muricholic acid [T-βMCA]) from the alternative pathway in the plasma of patients and mice. Fecal microbial transplantation (FMT), the ileum-specific farnesoid X receptor (FXR) agonist fexaramine, or glycodeoxycholic acid (GDCA) compensated dysbiosis-associated BA abnormalities and circumvent primary resistance to PD-1 blockade. GDCA curtailed ABX-induced MAdCAM-1 downregulation and T cell exhaustion in tumors. Subclinical cholestasis defined by elevation of γ-glutamyl transferase (γGT) correlated with increased TCDCA and decreased soluble MAdCAM-1 in plasma and predicted poor survival in multivariate analyses in six cohorts of patients who received immunotherapy. Hence, subclinical cholestasis accompanies gut dysbiosis, paving the way to immunoresistance.

Background:Clustering analysis is a foundational step in exploratory data analysis workflows, with dimensionality reduction methods commonly used to visualize multidimensional data in lower-dimensional spaces and infer sample clustering. Principal Component Analysis (PCA) is widely applied in metabolomics but is often suboptimal for clustering visualization. Metabolomics data often require specialized manipulations such as blank removal, quality control adjustments, and data transformations that demand efficient visualization tools. However, the lack of user-friendly tools for clustering without computational expertise presents a challenge for metabolomics researchers. ClusterApp addresses this gap as a web application that performs Principal Coordinate Analysis (PCoA), expanding clustering alternatives in metabolomics. Built on a QIIME 2 Docker image, it enables PCoA computation and Emperor plot visualization. The app supports data input from GNPS, GNPS2, or user-provided spreadsheets. Freely available, ClusterApp can be locally installed as a Docker image or integrated into Jupyter notebooks, offering accessibility and flexibility to diverse users. Results:To demonstrate the data preprocessing techniques available in ClusterApp, we analyzed two Liquid Chromatography coupled to Tandem Mass Spectrometry (LC-MS/MS) metabolomics datasets: one exploring metabolomic differences in mouse tissue samples and another investigating coral life history stages. Among the dissimilarity measures available, the Bray-Curtis measure effectively highlighted key metabolomic variations and patterns across both datasets. Targeted filtering significantly enhanced data reliability by retaining biologically relevant features, 10,617 in the coral dataset and 7,341 in the mouse dataset while eliminating noise. The combination of Total Ion Current (TIC) normalization and auto-scaling improved clustering resolution, revealing distinct separations in tissue types and life stages. ClusterApp's flexible features, such as customizable blank removal and group selection, provided tailored analyses, enhancing visualization and interpretation of metabolomic profiles. Conclusion:ClusterApp addresses the need for accessible, dynamic tools for exploratory data analysis in metabolomics. By coupling data transformation capabilities with PCoA on multiple dissimilarity matrices, it provides a versatile solution for clustering analysis. Its web interface and Docker-based deployment offer flexibility, accommodating a wide range of use cases through graphical or programmatic interactions. ClusterApp empowers researchers to uncover meaningful patterns and relationships in metabolomics data without requiring cumbersome data manipulation or advanced bioinformatics expertise.

People with cystic fibrosis (pwCF) have reduced mucociliary clearance in their airways, leading to the build-up of thick, sticky mucus susceptible to opportunistic infection. A new treatment, comprised of three small molecule drugs called Elexacaftor/Tezacaftor/Ivacaftor (ETI), has improved mucociliary clearance and lung function in pwCF, but how this therapy alters lung infections is poorly understood. This study experimentally modeled the biochemical changes in airway mucus caused by ETI to determine its effect on the CF lung microbiome structure and function. We prepared Artificial Sputum Medium (ASM) with reduced primary carbon sources (amino acids, deoxyribonucleic acid DNA, and mucin) to mimic the effects of ETI on mucus biochemistry due to improved mucociliary clearance and reduced pulmonary inflammation. The control and modified ASM were inoculated with pure CF pathogens or mixed-species communities and then grown in oxic and anoxic conditions, followed by multi-omics data analysis. Although oxygen strongly altered the community structure, the nutrient depletions in ASM had little effect. Instead, the reduced carbon sources altered the physiology of the collective community and its individual pathogens. This included modified growth kinetics in addition to altered nitrogen and nucleotide metabolism. Under reduced amino acid concentrations, a known effect of ETI on the sputum metabolome, the production of both Pseudomonas aeruginosa’s quinolones and rhamnolipids was significantly reduced. This indirect effect of ETI translates to reduced killing of competing pathogens and reduced toxicity to epithelial cells isolated from the airways of explanted human lung tissues. These findings indicate that ETI may provide further benefit to pwCF by reducing the competition and virulence of its principal pathogen and highlight how microenvironmental effects can have powerful impacts on polymicrobial infections.

Background The airways of people with cystic fibrosis (pwCF) are often colonized by a variety of different microbes. Although much effort has been put into cataloguing the impact of medication on the identities and abundances of these microbes, far less has been directed towards examining this from an ecological perspective, i.e., examining how medications affect the network and types of interactions between microbes. Methods In the current work, we generated an ecological model of the CF airway microbiome and examined how medications affect interactions between co-habiting airway microbiota in six pwCF. Ecological interactions were inferred from a generalized Lotka-Volterra model, and the impact of medications was determined by principal component(s) regression analysis. Results For the majority of the subjects studied, antimicrobial interventions had relatively little impact on the CF airway microbial ecology, and even appeared to stabilize ecological interactions between the microbiota. However, the microbial ecosystem in some individuals was more sensitive to external perturbations. More surprisingly, we found that some non-antimicrobial medications, and also certain carriers and excipients affect the ecosystem. Conclusions Medications affect the ecology of the CF airway microbiota. These impacts appear to be very patient-specific. We also note that some nominally non-bioactive ingredients in medications can also potentially impact the CF airway ecosystem. Our data highlight the importance of collecting patient-specific data and in employing suitable computational frameworks for disentangling medication-microbiota interactions in vivo.

Ecological guilds are groups of organisms that utilize the same class of resources and occupy similar niches, regardless of their taxonomic identities. Here we propose the Guild Model for Cystic Fibrosis Airway Microbial Ecology, which considers the ecological function and wider role of each microbe in the ecosystem. This model consists of four functional guilds: (i) "Brewers" metabolize host-derived substrates (e.g., mucins) and produce fermentation products; (ii) "Drunkards" exploit the metabolic niche built by Brewers, consuming fermentation products and secreting exopolysaccharides to build biofilms; (iii) "Putrifiers" produce toxic compounds causing inflammation and tissue necrosis; and (iv) "Nihilists" are specialist pathogens characterized by intracellular or lytic life cycles and cytotoxin production. By focusing on microbial function and the broader community context, this model offers a refined framework for interpreting cystic fibrosis airway ecology. Although developed for CF, the Guild Model is adaptable to other diseases influenced by microbial ecology.

Metabolites derived from the intestinal microbiota, including bile acids (BA), extensively modulate vertebrate physiology, including development1, metabolism2, 3-4, immune responses5, 6-7 and cognitive function8. However, to what extent host responses balance the physiological effects of microbiota-derived metabolites remains unclear9,10. Here, using untargeted metabolomics of mouse tissues, we identified a family of BA-methylcysteamine (BA-MCY) conjugates that are abundant in the intestine and dependent on vanin 1 (VNN1), a pantetheinase highly expressed in intestinal tissues. This host-dependent MCY conjugation inverts BA function in the hepatobiliary system. Whereas microbiota-derived free BAs function as agonists of the farnesoid X receptor (FXR) and negatively regulate BA production, BA-MCYs act as potent antagonists of FXR and promote expression of BA biosynthesis genes in vivo. Supplementation with stable-isotope-labelled BA-MCY increased BA production in an FXR-dependent manner, and BA-MCY supplementation in a mouse model of hypercholesteraemia decreased lipid accumulation in the liver, consistent with BA-MCYs acting as intestinal FXR antagonists. The levels of BA-MCY were reduced in microbiota-deficient mice and restored by transplantation of human faecal microbiota. Dietary intervention with inulin fibre further increased levels of both free BAs and BA-MCY levels, indicating that BA-MCY production by the host is regulated by levels of microbiota-derived free BAs. We further show that diverse BA-MCYs are also present in human serum. Together, our results indicate that BA-MCY conjugation by the host balances host-dependent and microbiota-dependent metabolic pathways that regulate FXR-dependent physiology.

Hepatocellular carcinoma (HCC) has a higher incidence in males and is a leading cause of cancer-related deaths, which lacks effective therapies and surveillance markers. Using a murine model of bile acid excess (farnesoid X receptor and small heterodimer partner double knockout, DKO), which phenocopies many aspects of HCC, including sex differences, we investigated the links between sex, bile acid metabolism, and microbial composition. Unexpectedly, the increase in the ratios of carcinogenic deoxycholic acid (DCA) was similar between DKO males with HCC and cancer-resistant DKO females. However, both taurine-conjugated and free-cholic acid (CA), sharply increased in the serum of DKO males with free-CA comprising 65% of the bile acid pool, whereas DKO female serum was mostly comprised of conjugated bile acids. Unlike such sex differences in DKO serum composition, conjugated bile acids were predominant in the hepatic BA pool irrespective of the sex or genotype, as expected. Fecal and cecal microbiota - many of which harbor bile acid transformation/ deconjugation capacity- were altered in DKO mice in a sex-specific manner. Untargeted fecal metabolite analysis showed differences in bile acids, phospholipids, and oxidized fatty acids between the genotypes, with DKO females excreting more sulphated and oxidized CA than tumor-bearing DKO males. Further analysis revealed a direct correlation between unconjugated CA levels with the abundance of the microbial genus Faecalibaculum in the DKO HCC model. These findings suggest distinct sex-specific changes in cecal and fecal microbiota, and BA composition may be leveraged in combination as a potential tool for HCC surveillance.

Obtaining sputum samples from people with cystic fibrosis (pwCF) for microbiology has become challenging due to the positive clinical effects of the cystic fibrosis transmembrane conductance regulator modulator therapy, elexacaftor-tezacaftor-ivacaftor (ETI). Although ETI improves lung function and reduces sputum production, recent data shows that bacterial pathogens persist, making continued monitoring of infection important. As an alternative to sputum sampling, this study developed a non-invasive technique called 'Cough Breath' (CB) to identify volatile organic compounds (VOCs) in exhaled breath condensate (EBC) and link them to cystic fibrosis (CF) bacterial pathogens using purge and trap GC-MS. The CB culturing approach was able to isolate pathogens from expectorated particulates simultaneously with EBC collection; however, culturing positivity was low, with 6% of samples collected (n=47) positive for either Pseudomonas aeruginosa or Staphylococcus aureus. From EBC, we identified VOCs matching those uniquely produced by P. aeruginosa (7), S. aureus (12), Achromobacter xylosoxidans (8) and Granulicatella adiacens (2); however, the overall detection rate was also low. Expanding to VOCs produced across multiple pathogens identified 30 frequently detected in the EBC of pwCF, including 2,3-pentanedione, propyl pyruvate, oxalic acid diallyl ester, methyl isobutyl ketone, methyl nitrate, 2-propenal, acetonitrile, acetoin and 2,3-butanedione. Comparing isolate volatilomes and EBC samples from the same pwCF enhanced detection rates with key VOCs, such as 2,3-pentanedione (86%) and propyl pyruvate (83%), in P. aeruginosa isolates. Further investigation showed that VOC production differed across strains and at different growth phases, creating variability that may explain the overall low EBC detection rate. Although this study successfully cultured CF pathogens from cough particulates and matched their unique VOCs in EBC samples, our results indicate that microbial volatiles more generally indicative of infection, such as 2,3-pentanedione, may have the most utility in aiding diagnostics in pwCF on ETI who have reduced sputum production in the clinic.

Coral bleaching is one of the greatest threats to the persistence of tropical reef ecosystems. This necessitates identification of attributes associated with coral resistance and resilience to thermal stress, both within and between generations. Here, we use metabolomics to investigate the intergenerational biochemical signatures associated with heat-induced bleaching of Montipora capitata (the rice coral). By selectively breeding bleaching resistant or susceptible parents, we find metabolomic signatures of parental bleaching phenotype in sperm, eggs, embryos, larvae, and subsequent juvenile corals. Metabolome source mapping shows that these thermal tolerance signatures are from both coral host and algal symbiont, spanning a variety of molecular families. One of the strongest markers of intergenerational heat tolerance is the saturation state of DGCC betaine lipids, a molecular family previously associated with thermal tolerance in dinoflagellate symbionts of corals. Though DGCC lipid saturation state is strongly linked to algal genotypes, even coral progeny containing the more thermally susceptible Cladocopium algae show increased saturation of this lipid group if their parents had resisted recent bleaching events. This work provides evidence for biochemical inheritance as a potential mechanism for intergenerational acclimatization to warming oceans, which has substantial implications for reef conservation and restoration in the face of climate change.

The susceptibility of corals to environmental stress is determined by complex interactions between host genetic variation and the Symbiodiniaceae family community. We exposed genotypes of Montipora capitata hosting primarily Cladocopium or Durusdinium symbionts to ambient conditions and an 8-day heat stress. Symbionts' cell surface glycan composition differed between genera and was significantly affected by temperature and oxidative stress. The metabolic profile of coral holobionts was primarily shaped by symbionts identity, but was also strongly responsive to oxidative stress. At peak temperature stress, betaine lipids in Cladocopium were remodeled to more closely resemble the abundance and saturation state of Durusdinium symbionts, which paralleled a larger metabolic shift in Cladocopium. Exploring how Symbiodiniaceae members regulate stress and host-symbiont affinity helps identify the traits contributing to coral resilience under climate change.

The infant brain and gut microbiome both develop rapidly in early infancy. Growing evidence indicates that the gut microbiome plays a critical role in shaping neurodevelopment early in life, possibly through effects on brain regions involved in affective, interoceptive, and sensory processing. This study used magnetic resonance imaging (MRI) and whole genome sequencing of fecal samples to examine associations between the gut microbiome and brain structures in infants at 2 weeks of age. We identified significant relationships between specific gut microbiome characteristics and brain volumes in key regions involved in affective, sensory, and interoceptive processing. Our most consistent findings were associations between gut microbiome and insula volume, suggesting that the insula may be particularly sensitive to gut microbiome influences during the neonatal period. Specifically, a significant negative association between insula volume and the abundance of Veillonella was observed. Alpha diversity (Shannon) and functional pathways were also related to insula structure. Enterobacter was negatively associated with thalamus volume. These findings contribute to the growing evidence of a developing gut-brain axis, highlighting links between the gut and brain as early as 2 weeks of age. Future research should investigate the mechanisms by which specific microbial features impact neurodevelopment by way of the insula, as well as explore the potential long-term implications of these early relationships on sensory, interoceptive, and affective processing, and behavioral outcomes.

Conjugated bile acids (BAs) are multi-functional detergents in the gastrointestinal (GI) tract produced by the liver enzyme bile acid-CoA:amino acid N-acyltransferase (BAAT) and by the microbiome from the acyltransferase activity of bile salt hydrolase (BSH). Humans with inflammatory bowel disease (IBD) have an enrichment in both host and microbially conjugated BAs (MCBAs), but their impacts on GI inflammation are not well understood. We investigated the role of host-conjugated BAs in a mouse model of colitis using a BAAT knockout background. Baat-/- KO mice have severe phenotypes in the colitis model that were rescued by supplementation with taurocholate (TCA). Gene expression and histology showed that this rescue was due to an improved epithelial barrier integrity and goblet cell function. However, metabolomics also showed that TCA supplementation resulted in extensive metabolism to secondary BAs. We therefore investigated the BSH activity of diverse gut bacteria on a panel of conjugated BAs and found broad hydrolytic capacity depending on the bacterium and the amino acid conjugate. The complexity of this microbial BA hydrolysis led to the exploration of bsh genes in metagenomic data from human IBD patients. Certain bsh sequences were enriched in people with Crohn's disease particularly that from Ruminococcus gnavus. This study shows that both host and microbially conjugated BAs may provide benefits to those with IBD, but this is dictated by a delicate balance between BA conjugation/deconjugation based on the bsh genes present.

Progression of chronic lung disease may lead to the requirement for lung transplant (LTx). Despite improvements in short-term survival after LTx, chronic lung allograft dysfunction (CLAD) remains a critical challenge for long-term survival. This study investigates the molecular and microbial relationships between underlying lung disease and the development of CLAD in bronchoalveolar lavage fluid (BALF) from subjects post-LTx, which is crucial for tailoring treatment strategies specific to allograft dysfunctions. Paired 16S rRNA gene amplicon sequencing and untargeted LC–MS/MS metabolomics were performed on 856 BALF samples collected over 10 years from LTx recipients (n = 195) with alpha-1-antitrypsin disease (AATD, n = 23), cystic fibrosis (CF, n = 47), chronic obstructive pulmonary disease (COPD, n = 78), or pulmonary fibrosis (PF, n = 47). Data were analyzed using random forest (RF) machine learning and multivariate statistics for associations with underlying disease and CLAD development. The BALF microbiome and metabolome after LTx differed significantly according to the underlying disease state (PERMANOVA, p = 0.001), with CF and AATD demonstrating distinct microbiome and metabolome profiles, respectively. Uniqueness in CF was mainly driven by Pseudomonas abundance and its metabolites, whereas AATD had elevated levels of phenylalanine and a lack of shared metabolites with the other underlying diseases. BALF microbiome and metabolome composition were also distinct between those who did or did not develop CLAD during the sample collection period (PERMANOVA, p = 0.001). An increase in the average abundance of Veillonella (AATD, COPD) and Streptococcus (CF, PF) was associated with CLAD development, and decreases in the abundance of phenylalanine-derivative alkaloids (CF, COPD) and glycerophosphorylcholines (CF, COPD, PF) were signatures of the CLAD metabolome. Although the relative abundance of Pseudomonas was not associated with CLAD, the abundance of its virulence metabolites, including siderophores, quorum-sensing quinolones, and phenazines, were elevated in those with CF who developed CLAD. There was a positive correlation between the abundance of these molecules and the abundance of Pseudomonas in the microbiome, but there was no correlation between their abundance and the time in which BALF samples were collected post-LTx. The BALF microbiome and metabolome after LTx are particularly distinct in those with underlying CF and AATD. These data reflect those who developed CLAD, with increased virulence metabolite production from Pseudomonas, an aspect of CF CLAD cases. These findings shed light on disease-specific microbial and metabolic signatures in LTx recipients, offering valuable insights into the underlying causes of allograft rejection.

Ectopic pregnancy (EP) is the leading cause of maternal morbidity and mortality in the first trimester. Using an untargeted metabolomic approach, we sought to identify putative plasma biomarkers using tandem liquid chromatography–mass spectrometry for the detection of tubal EP. This case-control study included the prospective recruitment of 50 tubal EP cases and 50 early intrauterine pregnancy controls. To avoid over-fitting, logistic regression models were developed in a randomly selected discovery group (30 cases vs. 30 controls) and validated in the test group (20 cases vs. 20 controls). In total, 585 mass spectral features were detected, of which 221 molecular features were significantly altered in EP plasma (p < 0.05). Molecular networking and metabolite identification was employed using the Global Natural Products Social Molecular Networking (GNPS) database, which identified 97 metabolites at a high confidence level. Top significant metabolites include subclasses of sphingolipids, carnitines, glycerophosphocholines, and tryptophan metabolism. The top regression model, consisting of D-erythro-sphingosine and oleoyl-carnitine, was validated in a test group and achieved an area under receiving operating curve (AUC) (95% CI) = 0.962 (0.910–1) with a sensitivity of 100% and specificity of 95.9%. Metabolite alterations indicate alterations related to inflammation and abnormal placentation in EP. The validation of these metabolite biomarkers in the future could potentially result in improved early diagnosis.

Bile acids (BAs) are steroid detergents in bile that contribute to the absorption of fats and fat-soluble vitamins while shaping the gut microbiome because of their antimicrobial properties1-4. Here we identify the enzyme responsible for a mechanism of BA metabolism by the gut microbiota involving amino acid conjugation to the acyl-site of BAs, thus producing a diverse suite of microbially conjugated bile acids (MCBAs). We show that this transformation is mediated by acyltransferase activity of bile salt hydrolase (bile salt hydrolase/transferase, BSH/T). Clostridium perfringens BSH/T rapidly performed acyl transfer when provided various amino acids and taurocholate, glycocholate or cholate, with an optimum at pH 5.3. Amino acid conjugation by C. perfringens BSH/T was diverse, including all proteinaceous amino acids except proline and aspartate. MCBA production was widespread among gut bacteria, with strain-specific amino acid use. Species with similar BSH/T amino acid sequences had similar conjugation profiles and several bsh/t alleles correlated with increased conjugation diversity. Tertiary structure mapping of BSH/T followed by mutagenesis experiments showed that active site structure affects amino acid selectivity. These MCBA products had antimicrobial properties, where greater amino acid hydrophobicity showed greater antimicrobial activity. Inhibitory concentrations of MCBAs reached those measured natively in the mammalian gut. MCBAs fed to mice entered enterohepatic circulation, in which liver and gallbladder concentrations varied depending on the conjugated amino acid. Quantifying MCBAs in human faecal samples showed that they reach concentrations equal to or greater than secondary and primary BAs and were reduced after bariatric surgery, thus supporting MCBAs as a significant component of the BA pool that can be altered by changes in gastrointestinal physiology. In conclusion, the inherent acyltransferase activity of BSH/T greatly diversifies BA chemistry, creating a set of previously underappreciated metabolites with the potential to affect the microbiome and human health.

Microbes play vital roles across coral reefs both in the environment and inside and upon macrobes (holobionts), where they support critical functions such as nutrition and immune system modulation. These roles highlight the potential ecosystem-level importance of microbes, yet most knowledge of microbial functions on reefs is derived from a small set of holobionts such as corals and sponges. Declining seawater pH — an important global coral reef stressor — can cause ecosystem-level change on coral reefs, providing an opportunity to study the role of microbes at this scale. We use an in situ experimental approach to test the hypothesis that under such ocean acidification (OA), known shifts among macrobe trophic and functional groups may drive a general ecosystem-level response extending across macrobes and microbes, leading to reduced distinctness between the benthic holobiont community microbiome and the environmental microbiome. We test this hypothesis using genetic and chemical data from benthic coral reef community holobionts sampled across a pH gradient from CO2 seeps in Papua New Guinea. We find support for our hypothesis; under OA, the microbiome and metabolome of the benthic holobiont community become less compositionally distinct from the sediment microbiome and metabolome, suggesting that benthic macrobe communities are colonised by environmental microbes to a higher degree under OA conditions. We also find a simplification and homogenisation of the benthic photosynthetic community, and an increased abundance of fleshy macroalgae, consistent with previously observed reef microbialisation. We demonstrate a novel structural shift in coral reefs involving macrobes and microbes: that the microbiome of the benthic holobiont community becomes less distinct from the sediment microbiome under OA. Our findings suggest that microbialisation and the disruption of macrobe trophic networks are interwoven general responses to environmental stress, pointing towards a universal, undesirable, and measurable form of ecosystem changed.