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Stony corals, the engines and engineers of reef ecosystems, face unprecedented threats from anthropogenic environmental change. Corals are holobionts that comprise the cnidarian animal host and a diverse community of bacteria, archaea, viruses and eukaryotic microorganisms. Recent research shows that the bacterial microbiome has a pivotal role in coral biology. A healthy bacterial assemblage contributes to nutrient cycling and stress resilience, but pollution, overfishing and climate change can break down these symbiotic relationships, which results in disease, bleaching and, ultimately, coral death. Although progress has been made in characterizing the spatial-temporal diversity of bacteria, we are only beginning to appreciate their functional contribution. In this Review, we summarize the ecological and metabolic interactions between bacteria and other holobiont members, highlight the biotic and abiotic factors influencing the structure of bacterial communities and discuss the impact of climate change on these communities and their coral hosts. We emphasize how microbiome-based interventions can help to decipher key mechanisms underpinning coral health and promote reef resilience. Finally, we explore how recent technological developments may be harnessed to address some of the most pressing challenges in coral microbiology, providing a road map for future research in this field.In this Review, Voolstra, Raina, Peixoto and colleagues discuss our current knowledge of the function and role of the bacterial microbiome in coral health and disease, and elucidate the response of the host-associated bacteria to global change, which bears implications for coral reef conservation.

Abstract Corals live in a complex, multipartite symbiosis with diverse microbes across kingdoms, some of which are implicated in vital functions, such as those related to resilience against climate change. However, knowledge gaps and technical challenges limit our understanding of the nature and functional significance of complex symbiotic relationships within corals. Here, we provide an overview of the complexity of the coral microbiome focusing on taxonomic diversity and functions of well-studied and cryptic microbes. Mining the coral literature indicate that while corals collectively harbour a third of all marine bacterial phyla, known bacterial symbionts and antagonists of corals represent a minute fraction of this diversity and that these taxa cluster into select genera, suggesting selective evolutionary mechanisms enabled these bacteria to gain a niche within the holobiont. Recent advances in coral microbiome research aimed at leveraging microbiome manipulation to increase coral’s fitness to help mitigate heat stress-related mortality are discussed. Then, insights into the potential mechanisms through which microbiota can communicate with and modify host responses are examined by describing known recognition patterns, potential microbially derived coral epigenome effector proteins and coral gene regulation. Finally, the power of omics tools used to study corals are highlighted with emphasis on an integrated host–microbiota multiomics framework to understand the underlying mechanisms during symbiosis and climate change-driven dysbiosis. Corals live in intimate relationships with an intricate collection of microbes that are crucial for their functioning; therefore, understanding the molecular basis of the interactions of the coral host and its associated microbiome is vital for coral resilience in a warming ocean.

α-glucosidase inhibitors represent an important class of type 2 antidiabetic drugs and they act by lowering postprandial hyperglycemia. Today, only three synthetic inhibitors exist on the market, and there is a need for novel, natural and more efficient molecules exhibiting this activity. In this study, we investigated the ability of Tamarix nilotica ethanolic and aqueous shoot extracts, as well as methanolic fractions prepared from aqueous crude extracts to inhibit α-glucosidase. Both, 50% ethanol and aqueous extracts inhibited α-glucosidase in a concentration-dependent manner, with IC 50 values of 12.5 μg/mL and 24.8 μg/mL, respectively. Importantly, α-glucosidase inhibitory activity observed in the T . nilotica crude extracts was considerably higher than pure acarbose (IC 50 = 151.1 μg/mL), the most highly prescribed α-glucosidase inhibitor on the market. When T . nilotica crude extracts were fractionated using methanol, enhanced α-glucosidase inhibitory activity was observed in general, with the highest observed α-glucosidase inhibitory activity in the 30% methanol fraction (IC 50 = 5.21 μg/mL). Kinetic studies further revealed a competitive reversible mechanism of inhibition by the plant extract. The phytochemical profiles of 50% ethanol extracts, aqueous extracts, and the methanolic fractions were investigated and compared using a metabolomics approach. Statistical analysis revealed significant differences in the contents of the crude extracts and fractions and potentially identified the molecules that were most responsible for these observed variations. Higher α-glucosidase inhibitory activity was associated with an enrichment of terpenoids, fatty acids, and flavonoids. Among the identified molecules, active compounds with known α-glucosidase inhibitory activity were detected, including unsaturated fatty acids, triterpenoids, and flavonoid glycosides. These results put forward T . nilotica as a therapeutic plant for type 2 diabetes and a source of α-glucosidase inhibitors.

By controlling nutrient cycling and biomass production at the base of the food web, interactions between phytoplankton and bacteria represent a fundamental ecological relationship in aquatic environments. Although typically studied over large spatiotemporal scales, emerging evidence indicates that this relationship is often governed by microscale interactions played out within the region immediately surrounding individual phytoplankton cells. This microenvironment, known as the phycosphere, is the planktonic analogue of the rhizosphere in plants. The exchange of metabolites and infochemicals at this interface governs phytoplankton–bacteria relationships, which span mutualism, commensalism, antagonism, parasitism and competition. The importance of the phycosphere has been postulated for four decades, yet only recently have new technological and conceptual frameworks made it possible to start teasing apart the complex nature of this unique microbial habitat. It has subsequently become apparent that the chemical exchanges and ecological interactions between phytoplankton and bacteria are far more sophisticated than previously thought and often require close proximity of the two partners, which is facilitated by bacterial colonization of the phycosphere. It is also becoming increasingly clear that while interactions taking place within the phycosphere occur at the scale of individual microorganisms, they exert an ecosystem-scale influence on fundamental processes including nutrient provision and regeneration, primary production, toxin biosynthesis and biogeochemical cycling. Here we review the fundamental physical, chemical and ecological features of the phycosphere, with the goal of delivering a fresh perspective on the nature and importance of phytoplankton–bacteria interactions in aquatic ecosystems. This Review Article discusses the physical, chemical and ecological features of the phycosphere, the microenvironment surrounding individual phytoplankton cells, and its importance during phytoplankton–bacteria interactions in aquatic ecosystems.

Unicellular eukaryotic phytoplankton, such as diatoms, rely on microbial communities for survival despite lacking specialized compartments to house microbiomes (e.g., animal gut). Microbial communities have been widely shown to benefit from diatom excretions that accumulate within the microenvironment surrounding phytoplankton cells, known as the phycosphere. However, mechanisms that enable diatoms and other unicellular eukaryotes to nurture specific microbiomes by fostering beneficial bacteria and repelling harmful ones are mostly unknown. We hypothesized that diatom exudates may tune microbial communities and employed an integrated multiomics approach using the ubiquitous diatom Asterionellopsis glacialis to reveal how it modulates its naturally associated bacteria. We show that A. glacialis reprograms its transcriptional and metabolic profiles in response to bacteria to secrete a suite of central metabolites and two unusual secondary metabolites, rosmarinic acid and azelaic acid. While central metabolites are utilized by potential bacterial symbionts and opportunists alike, rosmarinic acid promotes attachment of beneficial bacteria to the diatom and simultaneously suppresses the attachment of opportunists. Similarly, azelaic acid enhances growth of beneficial bacteriawhile simultaneously inhibiting growth of opportunistic ones.We further show that the bacterial response to azelaic acid is numerically rare but globally distributed in the world’s oceans and taxonomically restricted to a handful of bacterial genera. Our results demonstrate the innate ability of an important unicellular eukaryotic group to modulate select bacteria in their microbial consortia, similar to higher eukaryotes, using unique secondary metabolites that regulate bacterial growth and behavior inversely across different bacterial populations.

Ammonia-oxidizing archaea (AOA) are now implicated in exerting significant control over the form and availability of reactive nitrogen species in marine environments. Detailed studies of specific metabolic traits and physicochemical factors controlling their activities and distribution have not been well constrained in part due to the scarcity of isolated AOA strains. Here, we report the isolation of two new coastal marine AOA, strains PS0 and HCA1. Comparison of the new strains to Nitrosopumilus maritimus strain SCM1, the only marine AOA in pure culture thus far, demonstrated distinct adaptations to pH, salinity, organic carbon, temperature, and light. Strain PS0 sustained nearly 80% of ammonia oxidation activity at a pH as low as 5.9, indicating that coastal strains may be less sensitive to the ongoing reduction in ocean pH. Notably, the two novel isolates are obligate mixotrophs that rely on uptake and assimilation of organic carbon compounds, suggesting a direct coupling between chemolithotrophy and organic matter assimilation in marine food webs. All three isolates showed only minor photoinhibition at 15 µE⋅m ⁻²⋅s ⁻¹ and rapid recovery of ammonia oxidation in the dark, consistent with an AOA contribution to the primary nitrite maximum and the plausibility of a diurnal cycle of archaeal ammonia oxidation activity in the euphotic zone. Together, these findings highlight an unexpected adaptive capacity within closely related marine group I Archaea and provide new understanding of the physiological basis of the remarkable ecological success reflected by their generally high abundance in marine environments.

Chemicals inducing chemotaxis have been characterised for over 60 years across hundreds of publications. Without any synthesis of these scattered results, our current understanding of the molecules affecting prokaryotic behaviours is fragmented. Here, we examined 341 publications to assemble a comprehensive database of prokaryotic chemoeffectors, compiling the effect (attractant, repellent or neutral) of 926 chemicals previously tested and the chemotactic behaviour of 394 strains. Our analysis reveals that (i) not all chemical classes trigger chemotaxis equally, in particular, amino acids and benzenoids are much stronger attractants than carbohydrates; (ii) over one-quarter of attractants tested are not used for growth but solely act as chemotactic signals; (iii) the prokaryote’s origin matters, as terrestrial strains respond to 50% more chemicals than those originating from human or marine biomes; (iv) repellents affect cell behaviour at concentrations 10-fold higher than attractants; (v) the effect of large molecules and the behaviour of bacteria other than Proteobacteria have been largely overlooked. Taken together, our findings provide a unifying view of the chemical characteristics that affect prokaryotic behaviours globally. In this meta-analysis, the authors compile results from 60 years of chemotaxis research into a database of prokaryotic chemoeffectors that compares and analyses their effects as attractant, repellent or neutral compounds, as well as the chemotactic behaviour of responding microorganisms.

This study aimed to evaluate the potential of phytochemicals from two native UAE plant species, Arthrocnemum macrostachyum and Tamarix nilotica , as anti-cancer agents. The plant extracts were obtained using two methods, maceration, and microwave-assisted extraction (MAE), and were subsequently evaluated for their in vitro cytotoxicity against three cancer cell lines: breast (MDA-MB-231), colon (HCT-116), and lung (A-549). Results suggest that: 1) MAE is more efficient than maceration in recovering metabolites from plant biomass based on measurements of total phenolic content, radical scavenging activity, and bioactivity of extracts based on in vitro cytotoxicity. 2) Only T . nilotica extracts were found to be bioactive based on cytotoxicity measurements. 3) Cancer cell lines displayed differential sensitivity to T . nilotica crude extracts, with breast cancer cells being the most sensitive and lung cancer cells being the least sensitive. 4) Solid-phase fractionation of T . nilotica crude extract using different percentages of methanol resulted in several fractions that were 100-fold more cytotoxic compared to the crude unfractionated extract. The 30% and 70% methanol fractions exhibited the highest cytotoxicity towards breast and colon cancer cell lines, respectively. 5) Untargeted metabolomics using UHPLC-Q-ToF-MS of T . nilotica crude extracts revealed 909 molecular features, of which only 327 were annotated using MS/MS fragmentation. The results suggest that T . nilotica extracts have potential as anti-cancer agents and that MAE is an efficient method for extracting phytochemicals from plant biomass. The study also revealed that cancer cell lines exhibited differential sensitivity to the extracts and that solid-phase fractionation of crude extract using different percentages of methanol can yield fractions that are more cytotoxic than the crude extract.

Significance In the surface ocean, organic matter released by phytoplankton and degraded by heterotrophic bacteria is a key step in the carbon cycle. Compounds important in this trophic link are poorly known, in part because of the thousands of chemicals making up marine dissolved organic matter. We cocultured a Roseobacter clade bacterium with the diatom Thalassiosira pseudonana and used gene expression changes to assay for compounds passed to the bacterium. A C ₃-sulfonate with no previously known role in the microbial food web was identified and subsequently shown to be an abundant diatom metabolite and actively cycling compound in seawater. This work identifies a missing component of the marine carbon and sulfur cycles. About half the carbon fixed by phytoplankton in the ocean is taken up and metabolized by marine bacteria, a transfer that is mediated through the seawater dissolved organic carbon (DOC) pool. The chemical complexity of marine DOC, along with a poor understanding of which compounds form the basis of trophic interactions between bacteria and phytoplankton, have impeded efforts to identify key currencies of this carbon cycle link. Here, we used transcriptional patterns in a bacterial-diatom model system based on vitamin B ₁₂ auxotrophy as a sensitive assay for metabolite exchange between marine plankton. The most highly up-regulated genes (up to 374-fold) by a marine Roseobacter clade bacterium when cocultured with the diatom Thalassiosira pseudonana were those encoding the transport and catabolism of 2,3-dihydroxypropane-1-sulfonate (DHPS). This compound has no currently recognized role in the marine microbial food web. As the genes for DHPS catabolism have limited distribution among bacterial taxa, T. pseudonana may use this sulfonate for targeted feeding of beneficial associates. Indeed, DHPS was both a major component of the T. pseudonana cytosol and an abundant microbial metabolite in a diatom bloom in the eastern North Pacific Ocean. Moreover, transcript analysis of the North Pacific samples provided evidence of DHPS catabolism by Roseobacter populations. Other such biogeochemically important metabolites may be common in the ocean but difficult to discriminate against the complex chemical background of seawater. Bacterial transformation of this diatom-derived sulfonate represents a previously unidentified and likely sizeable link in both the marine carbon and sulfur cycles.

Lyophilization is the “gold standard” for drying plant extracts, which is important in preserving their quality and extending their shelf-life. Compared to other methods of drying plant extracts, lyophilization is costlier due to equipment, material and operational expenses. An alternative method is post-extraction oven-drying, but the effects of this process on extract quality are unknown. In this study, crude extracts from Arthrocnemum macrostachyum shoots were compared using three post-extraction drying methods (lyophilization and oven drying at 40 and 60 °C) and two extraction solvents (water and aqueous 50% ethanol). Untargeted metabolomics coupled with chemometrics analysis revealed that post extraction oven-drying resulted in the loss of up to 27% of molecular features when compared to lyophilization in water extracts only. In contrast, only 3% of molecular features were lost in aqueous 50% ethanol extracts when subjected to oven drying. That is to say, ethanol used as a solvent has a stabilizing effect on metabolites and enhances their resistance to thermal transformation in the oven. Collectively, oven-drying of extracts was as effective as lyophilization in preserving metabolites in extracts only when 50% ethanol was used as a solvent. The results presented in this paper demonstrate the value of selecting solvent-appropriate post-extraction drying methods.