Herbivore effects increase with latitude across the extent of a foundational seagrass

Climate change is altering the functioning of foundational ecosystems. While the direct effects of warming are expected to influence individual species, the indirect effects of warming on species interactions remain poorly understood. In marine systems, as tropical herbivores undergo poleward range expansion, they may change food web structure and alter the functioning of key habitats. While this process ('tropicalization') has been documented within declining kelp forests, we have a limited understanding of how this process might unfold across other systems. Here we use a network of sites spanning 23° of latitude to explore the effects of increased herbivory (simulated via leaf clipping) on the structure of a foundational marine plant (turtlegrass). By working across its geographic range, we also show how gradients in light, temperature and nutrients modified plant responses. We found that turtlegrass near its northern boundary was increasingly affected (reduced productivity) by herbivory and that this response was driven by latitudinal gradients in light (low insolation at high latitudes). By contrast, low-latitude meadows tolerated herbivory due to high insolation which enhanced plant carbohydrates. We show that as herbivores undergo range expansion, turtlegrass meadows at their northern limit display reduced resilience and may be under threat of ecological collapse.

Biosynthesis of Dolastatin 10 in Marine Cyanobacteria, a Prototype for Multiple Approved Cancer Drugs

Dolastatin 10, a potent tubulin-targeting marine anticancer natural product, provided the basis for the development of six FDA-approved antibody-drug conjugates. Through the screening of cyanobacterial Caldora penicillata environmental DNA libraries and metagenome sequencing, we identified its biosynthetic gene cluster. Functional prediction of 10 enzymes encoded in the 39 kb cluster supports the dolastatin 10 biosynthesis. The nonheme diiron monooxygenase DolJ was biochemically characterized to mediate the terminal thiazole formation in dolastatin 10.

Microbiomes of Thalassia testudinum throughout the Atlantic Ocean, Caribbean Sea, and Gulf of Mexico are influenced by site and region while maintaining a core microbiome

Plant microbiomes are known to serve several important functions for their host, and it is therefore important to understand their composition as well as the factors that may influence these microbial communities. The microbiome of Thalassia testudinum has only recently been explored, and studies to-date have primarily focused on characterizing the microbiome of plants in a single region. Here, we present the first characterization of the composition of the microbial communities of T. testudinum across a wide geographical range spanning three distinct regions with varying physicochemical conditions. We collected samples of leaves, roots, sediment, and water from six sites throughout the Atlantic Ocean, Caribbean Sea, and the Gulf of Mexico. We then analyzed these samples using 16S rRNA amplicon sequencing. We found that site and region can influence the microbial communities of T. testudinum, while maintaining a plant-associated core microbiome. A comprehensive comparison of available microbial community data from T. testudinum studies determined a core microbiome composed of 14 ASVs that consisted mostly of the family Rhodobacteraceae. The most abundant genera in the microbial communities included organisms with possible plant-beneficial functions, like plant-growth promoting taxa, disease suppressing taxa, and nitrogen fixers.

Characterizing transcriptomic responses to sediment stress across location and morphology in reef-building corals

Anthropogenic activities increase sediment suspended in the water column and deposition on reefs can be largely dependent on colony morphology. Massive and plating corals have a high capacity to trap sediments, and active removal mechanisms can be energetically costly. Branching corals trap less sediment but are more susceptible to light limitation caused by suspended sediment. Despite deleterious effects of sediments on corals, few studies have examined the molecular response of corals with different morphological characteristics to sediment stress. To address this knowledge gap, this study assessed the transcriptomic responses of branching and massive corals in Florida and Hawai'i to varying levels of sediment exposure. Gene expression analysis revealed a molecular responsiveness to sediments across species and sites. Differential Gene Expression followed by Gene Ontology (GO) enrichment analysis identified that branching corals had the largest transcriptomic response to sediments, in developmental processes and metabolism, while significantly enriched GO terms were highly variable between massive corals, despite similar morphologies. Comparison of DEGs within orthogroups revealed that while all corals had DEGs in response to sediment, there was not a concerted gene set response by morphology or location. These findings illuminate the species specificity and genetic basis underlying coral susceptibility to sediments.

Chlorinated Enyne Fatty Acid Amides from a Marine Cyanobacterium: Discovery of Taveuniamides L-M and Pharmacological Characterization of Taveuniamide F as a GPCR Antagonist with CNR1 Selectivity

NMR and MS/MS-based metabolomics of a cyanobacterial extract from Piti Bomb Holes, Guam, indicated the presence of unique enyne-containing halogenated fatty acid amides. We isolated three new compounds of this class, taveuniamides L-N (1-3), along with the previously reported taveuniamide F (4), which was the most abundant analog. The planar structures of the new compounds were established using 1D and 2D NMR as well as mass spectrometry. We established the configuration of this chemical class to be R at C-8 via Mosher's analysis of 4 after reduction of the carboxamide group. Our biological investigations with 4 revealed that the compound binds to the cannabinoid receptor CNR1, acting as an antagonist/inverse agonist in the canonical G-protein signaling pathways. In selectivity profiling against 168 GPCR targets using the β-arrestin functional assay, we found that 4 antagonizes GPR119, NPSR1b, CCR9, CHRM4, GPR120, HTR2A, and GPR103, in addition to CNR1. Interestingly, 4 showed a 6.8-fold selectivity for CNR1 over CNR2. The binding mode of 4 to CNR1 was investigated using docking and molecular dynamics simulations with both natural and unnatural stereoisomers, revealing important CNR1 residues for the interaction and also providing a possible reasoning for the observed CNR1/CNR2 selectivity.

Discovery and Anti-Inflammatory Activity of a Cyanobacterial Fatty Acid Targeting the Keap1/Nrf2 Pathway

The monounsaturated fatty acid 7(E)-9-keto-hexadec-7-enoic acid (1) and three structurally related analogues with different oxidation states and degrees of unsaturation (2-4) were discovered from a marine benthic cyanobacterial mat collected from Delta Shoal, Florida Keys. Their structures were elucidated using NMR spectroscopy and mass spectrometry. The structure of 1 contained an α,β-unsaturated carbonyl system, a key motif required for the activation of the Keap1/Nrf2-ARE pathway that is involved in the activation of antioxidant and phase II detoxification enzymes. Compounds 1-4 were screened in ARE-luciferase reporter gene assay using stably transfected HEK293 cells, and only 1 significantly induced Nrf2 activity at 32 and 10 µM, whereas 2-4 were inactive. As there is crosstalk between inflammation and oxidative stress, subsequent biological studies were focused on 1 to investigate its anti-inflammatory potential. Compound 1 induced Nqo1, a well-known target gene of Nrf2, and suppressed iNos transcript levels, which translated into reduced levels of nitric oxide in LPS-activated mouse macrophage RAW264.7 cells, a more relevant model for inflammation. RNA sequencing was performed to capture the effects of 1 on a global level and identified additional canonical pathways and upstream regulators involved in inflammation and immune response, particularly those related to multiple sclerosis. A targeted survey of marine cyanobacterial samples from other geographic locations, including Guam, suggested the widespread occurrence of 1. Furthermore, the previous isolation of 1 from marine diatoms and green algae implied a potentially important ecological role across marine algal eukaryotes and prokaryotes. The previous isolation from sea lettuce raises the possibility of dietary intervention to attenuate inflammation and related disease progression.

Linking bacterial tetrabromopyrrole biosynthesis to coral metamorphosis

An important factor dictating coral fitness is the quality of bacteria associated with corals and coral reefs. One way that bacteria benefit corals is by stimulating the larval to juvenile life cycle transition of settlement and metamorphosis. Tetrabromopyrrole (TBP) is a small molecule produced by bacteria that stimulates metamorphosis with and without attachment in a range of coral species. A standing debate remains, however, about whether TBP biosynthesis from live Pseudoalteromonas bacteria is the primary stimulant of coral metamorphosis. In this study, we create a Pseudoalteromonas sp. PS5 mutant lacking the TBP brominase gene, bmp2. Using this mutant, we confirm that the bmp2 gene is critical for TBP biosynthesis in Pseudoalteromonas sp. PS5. Mutation of this gene ablates the bacterium's ability in live cultures to stimulate the metamorphosis of the stony coral Porites astreoides. We further demonstrate that expression of TBP biosynthesis genes is strongest in stationary and biofilm modes of growth, where Pseudoalteromonas sp. PS5 might exist within surface-attached biofilms on the sea floor. Finally, we create a modular transposon plasmid for genomic integration and fluorescent labeling of Pseudoalteromonas sp. PS5 cells. Our results functionally link a TBP biosynthesis gene from live bacteria to a morphogenic effect in corals. The genetic techniques established here provide new tools to explore coral-bacteria interactions and could help to inform future decisions about utilizing marine bacteria or their products for coral restoration.

Investigating microbial size classes associated with the transmission of stony coral tissue loss disease (SCTLD)

Effective treatment and prevention of any disease necessitates knowledge of the causative agent, yet the causative agents of most coral diseases remain unknown, in part due to the difficulty of distinguishing the pathogenic microbe(s) among the complex microbial backdrop of coral hosts. Stony coral tissue loss disease (SCTLD) is a particularly destructive disease of unknown etiology, capable of transmitting through the water column and killing entire colonies within a matter of weeks. Here we used a previously described method to (i) isolate diseased and apparently healthy coral colonies within individual mesocosms containing filtered seawater with low microbial background levels; (ii) incubate for several days to enrich the water with coral-shed microbes; (iii) use tangential-flow filtration to concentrate the microbial community in the mesocosm water; and then (iv) filter the resulting concentrate through a sequential series of different pore-sized filters. To investigate the size class of microorganism(s) associated with SCTLD transmission, we used 0.8 µm pore size filters to capture microeukaryotes and expelled zooxanthellae, 0.22 µm pore size filters to capture bacteria and large viruses, and 0.025 µm pore size filters to capture smaller viruses. In an attempt to further refine which size fraction(s) contained the transmissible element of SCTLD, we then applied these filters to healthy "receiver" coral fragments and monitored them for the onset of SCTLD signs over three separate experimental runs. However, several factors outside of our control confounded the transmission results, rendering them inconclusive. As the bulk of prior studies of SCTLD in coral tissues have primarily investigated the associated bacterial community, we chose to characterize the prokaryotic community associated with all mesocosm 0.22 µm pore size filters using Illumina sequencing of the V4 region of the 16S rRNA gene. We identified overlaps with prior SCTLD studies, including the presence of numerous previously identified SCTLD bioindicators within our mesocosms. The identification in our mesocosms of specific bacterial amplicon sequence variants that also appear across prior studies spanning different collection years, geographic regions, source material, and coral species, suggests that bacteria may play some role in the disease.

Targeted and functional genomics approaches to the mechanism of action of lagunamide D, a mitochondrial cytotoxin from marine cyanobacteria

Lagunamide D, a cyanobacterial cyclodepsipeptide, exhibits potent antiproliferative activity against HCT116 colorectal cancer cells (IC50 5.1 nM), which were used to probe the mechanism of action. Measurements of metabolic activity, mitochondrial membrane potential, caspase 3/7 activity and cell viability indicate the rapid action of lagunamide D on mitochondrial function and downstream cytotoxic effects in HCT116 cells. Lagunamide D preferentially targets the G1 cell cycle population and arrests cells in G2/M phase at high concentration (32 nM). Transcriptomics and subsequent Ingenuity Pathway Analysis identified networks related to mitochondrial functions. Lagunamide D induced mitochondrial network redistribution at 10 nM, suggesting a mechanism shared with the structurally related aurilide family, previously reported to target mitochondrial prohibitin 1 (PHB1). Knockdown and chemical inhibition of ATP1A1 sensitized the cells to lagunamide D, as also known for aurilide B. We interrogated potential mechanisms behind this synergistic effect between lagunamide D and ATP1A1 knockdown by using pharmacological inhibitors and extended the functional analysis to a global level by performing a chemogenomic screen with a siRNA library targeting the human druggable genome, revealing targets that modulate susceptibility to lagunamide D. In addition to mitochondrial targets, the screen revealed hits involved in the ubiquitin/proteasome pathway, suggesting lagunamide D might exert its effects by additionally affecting proteostasis. Our analysis illuminated cellular processes of lagunamide D that can be modulated in parallel to mitochondrial functions. The identification of potential synergistic drug combinations that can alleviate undesirable toxicity may open possibilities to resurrect this class of compounds for anticancer therapy.

Rapid prototyping for quantifying belief weights of competing hypotheses about emergent diseases

Emerging diseases can have devastating consequences for wildlife and require a rapid response. A critical first step towards developing appropriate management is identifying the etiology of the disease, which can be difficult to determine, particularly early in emergence. Gathering and synthesizing existing information about potential disease causes, by leveraging expert knowledge or relevant existing studies, provides a principled approach to quickly inform decision-making and management efforts. Additionally, updating the current state of knowledge as more information becomes available over time can reduce scientific uncertainty and lead to substantial improvement in the decision-making process and the application of management actions that incorporate and adapt to newly acquired scientific understanding. Here we present a rapid prototyping method for quantifying belief weights for competing hypotheses about the etiology of disease using a combination of formal expert elicitation and Bayesian hierarchical modeling. We illustrate the application of this approach for investigating the etiology of stony coral tissue loss disease (SCTLD) and discuss the opportunities and challenges of this approach for addressing emergent diseases. Lastly, we detail how our work may apply to other pressing management or conservation problems that require quick responses. We found the rapid prototyping methods to be an efficient and rapid means to narrow down the number of potential hypotheses, synthesize current understanding, and help prioritize future studies and experiments. This approach is rapid by providing a snapshot assessment of the current state of knowledge. It can also be updated periodically (e.g., annually) to assess changes in belief weights over time as scientific understanding increases. Synthesis and applications: The rapid prototyping approaches demonstrated here can be used to combine knowledge from multiple experts and/or studies to help with fast decision-making needed for urgent conservation issues including emerging diseases and other management problems that require rapid responses. These approaches can also be used to adjust belief weights over time as studies and expert knowledge accumulate and can be a helpful tool for adapting management decisions.

Isolation and Biological Activity of Iezoside and Iezoside B, SERCA Inhibitors from Floridian Marine Cyanobacteria

Marine cyanobacteria are a rich source of bioactive natural products. Here, we report the isolation and structure elucidation of the previously reported iezoside (1) and its C-31 O-demethyl analogue, iezoside B (2), from a cyanobacterial assemblage collected at Loggerhead Key in the Dry Tortugas, Florida. The two compounds have a unique skeleton comprised of a peptide, a polyketide and a modified sugar unit. The compounds were tested for cytotoxicity and effects on intracellular calcium. Both compounds exhibited cytotoxic activity with an IC₅₀ of 1.5 and 3.0 μΜ, respectively, against A549 lung carcinoma epithelial cells and 1.0 and 2.4 μΜ against HeLa cervical cancer cells, respectively. In the same cell lines, compounds 1 and 2 show an increase in cytosolic calcium with approximate EC₅₀ values of 0.3 and 0.6 μΜ in A549 cells and 0.1 and 0.5 μΜ, respectively, in HeLa cells, near the IC₅₀ for cell viability, suggesting that the increase in cytosolic calcium is functionally related to the cytotoxicity of the compounds and consistent with their activity as SERCA (sarcoplasmic/endoplasmic reticulum Ca²⁺-ATPase) inhibitors. The structure-activity relationship provides evidence that structural changes in the sugar unit may be tolerated, and the activity is tunable. This finding has implications for future analogue synthesis and target interaction studies.

Linking bacterial tetrabromopyrrole biosynthesis to coral metamorphosis

An important factor dictating coral fitness is the quality of bacteria associated with corals and coral reefs. One way that bacteria benefit corals is by stimulating the larval to juvenile life cycle transition of settlement and metamorphosis. Tetrabromopyrrole (TBP) is a small molecule produced by bacteria that stimulates metamorphosis in a range of coral species. A standing debate remains, however, about whether TBP biosynthesis from live Pseudoalteromonas bacteria is the primary stimulant of coral metamorphosis. In this study, we create a Pseudoalteromonas sp. PS5 mutant lacking the TBP brominase gene, bmp2 . Using this mutant, we confirm that the bmp2 gene is critical for TBP biosynthesis in Pseudoalteromonas sp. PS5. Mutation of this gene ablates the bacterium's ability in live cultures to stimulate the metamorphosis of the stony coral Porites astreoides . We further demonstrate that expression of TBP biosynthesis genes is strongest in stationary and biofilm modes of growth, where Pseudoalteromonas sp. PS5 might exist within surface-attached biofilms on the sea floor. Finally, we create a modular transposon plasmid for genomic integration and fluorescent labeling of Pseudoalteromonas sp. PS5 cells. Our results functionally link a TBP biosynthesis gene from live bacteria to a morphogenic effect in corals. The genetic techniques established here provide new tools to explore coral-bacteria interactions and could help to inform future decisions about utilizing marine bacteria or their products for restoring degraded coral reefs.

Chemical and genomic characterization of a potential probiotic treatment for stony coral tissue loss disease

Considered one of the most devastating coral disease outbreaks in history, stony coral tissue loss disease (SCTLD) is currently spreading throughout Florida's coral reefs and the greater Caribbean. SCTLD affects at least two dozen different coral species and has been implicated in extensive losses of coral cover. Here we show Pseudoalteromonas sp. strain McH1-7 has broad-spectrum antibacterial activity against SCTLD-associated bacterial isolates. Chemical analyses indicated McH1-7 produces at least two potential antibacterials, korormicin and tetrabromopyrrole, while genomic analysis identified the genes potentially encoding an L-amino acid oxidase and multiple antibacterial metalloproteases (pseudoalterins). During laboratory trials, McH1-7 arrested or slowed disease progression on 68.2% of diseased Montastraea cavernosa fragments treated (n = 22), and it prevented disease transmission by 100% (n = 12). McH1-7 is the most chemically characterized coral probiotic that is an effective prophylactic and direct treatment for the destructive SCTLD as well as a potential alternative to antibiotic use.

Heterologous Production of the C33-C45 Polyketide Fragment of Anticancer Apratoxins in a Cyanobacterial Host

A polyketide synthase subcluster of cytotoxic apratoxin A was isolated from a Moorena bouillonii environmental DNA library and engineered with a thioesterase II domain for heterologous expression in the filamentous cyanobacterium Anabaena sp. PCC7120. Further engineering with a rhamnose-inducible promoter led to the production of (2R,3R,5R,7R)-3,7-dihydroxy-2,5,8,8-tetramethylnonanoic acid, a stereogenically rich chiral building block that is important to the efficient synthesis of apratoxin analogues, representing the first synthetic biology attempt for this type of polyketide fragment.

Biosynthesis of Lyngbyastatins 1 and 3, Cytotoxic Depsipeptides from an Okeania sp. Marine Cyanobacterium

Lyngbyastatins (Lbns) 1 (1) and 3 (2) belong to a group of cyclic depsipeptides that inhibit cancer cell proliferation. These compounds have been isolated from different marine cyanobacterial collections, while further development of these compounds relies on their lengthy total synthesis. Biosynthetic studies of these compounds can provide viable strategies to access these compounds and develop new analogs. In this study, we report the identification and characterization of one Lbn biosynthetic gene cluster (BGC) from the marine cyanobacterium Okeania sp. VPG18-21. We initially identified 1 and 2 in the organic extract by mass spectrometry and performed the targeted isolation of these compounds, which feature a (2S,3R)-3-amino-2-methylpentanoic acid (MAP) and a (2S,3R)-3-amino-2-methylhexanoic acid (Amha) moiety, respectively. Parallel metagenomic sequencing of VPG18-21 led to the identification of a putative Lbn BGC that encodes six megaenzymes (LbnA-F), including one polyketide synthase (PKS, LbnE), four nonribosomal peptide synthetases (NRPSs, LbnB-D and -F), and one PKS-NRPS hybrid (LbnA). Bioinformatic analysis of these enzymes suggested that the BGC produces 1 and 2. Furthermore, our biochemical studies of three recombinant adenylation domains uncovered their substrate specificities, supporting the identity of the BGC. Finally, we identified near-complete Lbn-like BGCs in the genomes of two other marine cyanobacteria.

Discovery, Synthesis, and Biological Evaluation of Anaenamides C and D from a New Marine Cyanobacterium, Hormoscilla sp

Our ongoing efforts to explore the chemical space associated with marine cyanobacteria from coral reefs of Guam have yielded two new members of the anaenamide family of natural products, anaenamides C (3) and D (4). These compounds were isolated from a novel Hormoscilla sp. (VPG16-58). Our phylogenetic profiling (16S rDNA) of this cyanobacterium indicated that VPG16-58 is taxonomically distinct from the previously reported producer of the anaephenes, VPG16-59 (Hormoscilla sp.), and other previously documented species of the genus Hormoscilla. The planar structures of 3 and 4 were determined via spectroscopic methods, and absolute configurations of the α-hydroxy acids were assigned by enantioselective HPLC analysis. To address the requirement for sufficient material for testing, we first adapted our published linear synthetic approach for 1 and 2 to generate anaenoic acid (7), which served as a point for diversification, providing the primary amides 3 and 4 from synthetic intermediates 5 and 6, respectively. The compounds were then tested for effects on HCT116 colon cancer cell viability and in an ARE-luciferase reporter gene assay for Nrf2 modulation using HEK293 human embryonic kidney cells. Our findings indicate that, in contrast to cytotoxic methyl esters 1 and 2, the primary amides 3 and 4 activate the Nrf2 pathway at noncytotoxic concentrations. Overall, our data suggest that the anaenamide scaffold is tunable to produce differential biological outcomes.

Metabolomics Approaches to Dereplicate Natural Products from Coral-Derived Bioactive Bacteria

Stony corals (Scleractinia) are invertebrates that form symbiotic relationships with eukaryotic algal endosymbionts and the prokaryotic microbiome. The microbiome has the potential to produce bioactive natural products providing defense and resilience to the coral host against pathogenic microorganisms, but this potential has not been extensively explored. Bacterial pathogens can pose a significant threat to corals, with some species implicated in primary and opportunistic infections of various corals. In response, probiotics have been proposed as a potential strategy to protect corals in the face of increased incidence of disease outbreaks. In this study, we screened bacterial isolates from healthy and diseased corals for antibacterial activity. The bioactive extracts were analyzed using untargeted metabolomics. Herein, an UpSet plot and hierarchical clustering analyses were performed to identify isolates with the largest number of unique metabolites. These isolates also displayed different antibacterial activities. Through application of in silico and experimental approaches coupled with genome analysis, we dereplicated natural products from these coral-derived bacteria from Florida's coral reef environments. The metabolomics approach highlighted in this study serves as a useful resource to select probiotic candidates and enables insights into natural product-mediated chemical ecology in holobiont symbiosis.

Anti-Inflammatory Dysidazirine Carboxylic Acid from the Marine Cyanobacterium Caldora sp. Collected from the Reefs of Fort Lauderdale, Florida

Dysidazirine carboxylic acid (1) was isolated from the lipophilic extract of a collection of the benthic marine cyanobacterium Caldora sp. from reefs near Fort Lauderdale, Florida. The planar structure of this new compound was determined by spectroscopic methods and comparisons between HRMS and NMR data with its reported methyl ester. The absolute configuration of the single chiral center was determined by the conversion of 1 to the methyl ester and the comparison of its specific rotation data with the two known methyl ester isomers, 2 and 3. Molecular sequencing with 16S rDNA indicated that this cyanobacterium differs from Caldora penicillata (Oscillatoriales) and represents a previously undocumented and novel Caldora species. Dysidazirine (2) showed weak cytotoxicity against HCT116 colorectal cancer cells (IC50 9.1 µM), while dysidazirine carboxylic acid (1) was non-cytotoxic. Similar cell viability patterns were observed in RAW264.7 cells with dysidazirine only (2), displaying cytotoxicity at the highest concentration tested (50 µM). The non-cytotoxic dysidazirine carboxylic acid (1) demonstrated anti-inflammatory activity in RAW264.7 cells stimulated with LPS. After 24 h, 1 inhibited the production of NO by almost 50% at 50 µM, without inducing cytotoxicity. Compound 1 rapidly decreased gene expression of the pro-inflammatory gene iNOS after 3 h post-LPS treatment and in a dose-dependent manner (IC50 ~1 µM); the downregulation of iNOS persisted at least until 12 h.

Combining tangential flow filtration and size fractionation of mesocosm water as a method for the investigation of waterborne coral diseases

The causative agents of most coral diseases today remain unknown, complicating disease response and restoration efforts. Pathogen identifications can be hampered by complex microbial communities naturally associated with corals and seawater, which create complicating "background noise" that can potentially obscure a pathogen's signal. Here, we outline an approach to investigate waterborne coral diseases that use a combination of coral mesocosms, tangential flow filtration, and size fractionation to reduce the impact of this background microbial diversity, compensate for unknown infectious dose, and further narrow the suspect pool of potential pathogens. As proof of concept, we use this method to compare the bacterial communities shed into six Montastraea cavernosa coral mesocosms and demonstrate this method effectively detects differences between diseased and healthy coral colonies. We found several amplicon sequence variants (ASVs) in the diseased mesocosms that represented 100% matches with ASVs identified in prior studies of diseased coral tissue, further illustrating the effectiveness of our approach. Our described method is an effective alternative to using coral tissue or mucus to investigate waterborne coral diseases of unknown etiology and can help more quickly narrow the pool of possible pathogens to better aid in disease response efforts. Additionally, this versatile method can be easily adapted to characterize either the entire microbial community associated with a coral or target-specific microbial groups, making it a beneficial approach regardless of whether a causative agent is suspected or is completely unknown.

Differential susceptibility of reef-building corals to deoxygenation reveals remarkable hypoxia tolerance

Ocean deoxygenation threatens the persistence of coastal ecosystems worldwide. Despite an increasing awareness that coastal deoxygenation impacts tropical habitats, there remains a paucity of empirical data on the effects of oxygen limitation on reef-building corals. To address this knowledge gap, we conducted laboratory experiments with ecologically important Caribbean corals Acropora cervicornis and Orbicella faveolata. We tested the effects of continuous exposure to conditions ranging from extreme deoxygenation to normoxia (~ 1.0 to 6.25 mg L^-1 dissolved oxygen) on coral bleaching, photophysiology, and survival. Coral species demonstrated markedly different temporal resistance to deoxygenation, and within a species there were minimal genotype-specific treatment effects. Acropora cervicornis suffered tissue loss and mortality within a day of exposure to severe deoxygenation (~ 1.0 mg L^-1), whereas O. faveolata remained unaffected after 11 days of continuous exposure to 1.0 mg L^-1. Intermediate deoxygenation treatments (~ 2.25 mg L^-1, ~ 4.25 mg L^-1) elicited minimal responses in both species, indicating a low oxygen threshold for coral mortality and coral resilience to oxygen concentrations that are lethal for other marine organisms. These findings demonstrate the potential for variability in species-specific hypoxia thresholds, which has important implications for our ability to predict how coral reefs may be affected as ocean deoxygenation intensifies. With deoxygenation emerging as a critical threat to tropical habitats, there is an urgent need to incorporate deoxygenation into coral reef research, management, and action plans to facilitate better stewardship of coral reefs in an era of rapid environmental change.

Marine reserves, fisheries ban, and 20 years of positive change in a coral reef ecosystem

By 2004, Belize was exhibiting classic fishing down of the food web. Groupers (Serranidae) and snappers (Lutjanidae) were scarce and fisheries turned to parrotfishes (Scarinae), leading to a 41% decline in their biomass. Several policies were enacted in 2009-2010, including a moratorium on fishing parrotfish and a new marine park with no-take areas. Using a 20-year time series on reef fish and benthos, we evaluated the impact of these policies approximately 10 years after their implementation. Establishment of the Southwater Caye Marine Reserve led to a recovery of snapper at 2 out of 3 sites, but there was no evidence of recovery outside the reserve. Snapper populations in an older reserve continued to increase, implying that at least 9 years is required for their recovery. Despite concerns over the feasibility of banning parrotfish harvest once it has become a dominant fin fishery, parrotfishes returned and exceeded biomass levels prior to the fishery. The majority of these changes involved an increase in parrotfish density; species composition and adult body size generally exhibited little change. Recovery occurred equally well in reserves and areas open to other forms of fishing, implying strong compliance. Temporal trends in parrotfish grazing intensity were strongly negatively associated with the cover of macroalgae, which by 2018 had fallen to the lowest levels observed since measurements began in 1998. Coral populations remained resilient and continued to exhibit periods of net recovery after disturbance. We found that a moratorium on parrotfish harvesting is feasible and appears to help constrain macroalgae, which can otherwise impede coral resilience.

Bifunctional Doscadenamides Activate Quorum Sensing in Gram-Negative Bacteria and Synergize with TRAIL to Induce Apoptosis in Cancer Cells

New cyanobacteria-derived bifunctional analogues of doscadenamide A, a LasR-dependent quorum sensing (QS) activator in Pseudomonas aeruginosa, characterized by dual acylation of the pyrrolinone core structure and the pendant side chain primary amine to form an imide/amide hybrid are reported. The identities of doscadenamides B-J were confirmed through total synthesis and a strategic focused library with different acylation and unsaturation patterns was created. Key molecular interactions for binding with LasR and a functional response through mutation studies coupled with molecular docking were identified. The structure-activity relationships (SARs) were probed in various Gram-negative bacteria, including P. aeruginosa and Vibrio harveyi, indicating that the pyrrolinone-N acyl chain is critical for full agonist activity, while the other acyl chain is dispensable or can result in antagonist activity, depending on the bacterial system. Since homoserine lactone (HSL) quorum sensing activators have been shown to act in synergy with TRAIL to induce apoptosis in cancer cells, selected doscadenamides were tested in orthogonal eukaryotic screening systems. The most potent QS agonists, doscadenamides S10-S12, along with doscadenamides F and S4 with partial or complete saturation of the acyl side chains, exhibited the most pronounced synergistic effects with TRAIL in triple negative MDA-MB-231 breast cancer cells. The overall correlation of the SAR with respect to prokaryotic and eukaryotic targets may hint at coevolutionary processes and intriguing host-bacteria relationships. The doscadenamide scaffold represents a non-HSL template for combination therapy with TRAIL pathway stimulators.

Genomic and Targeted Approaches Unveil the Cell Membrane as a Major Target of the Antifungal Cytotoxin Amantelide A

Amantelide A, a polyhydroxylated macrolide isolated from a marine cyanobacterium, displays broad-spectrum activity against mammalian cells, bacterial pathogens, and marine fungi. We conducted comprehensive mechanistic studies to identify the molecular targets and pathways affected by amantelide A. Our investigations relied on chemical structure similarities with compounds of known mechanisms, yeast knockout mutants, yeast chemogenomic profiling, and direct biochemical and biophysical methods. We established that amantelide A exerts its antifungal action by binding to ergosterol-containing membranes followed by pore formation and cell death, a mechanism partially shared with polyene antifungals. Binding assays demonstrated that amantelide A also binds to membranes containing epicholesterol or mammalian cholesterol, thus suggesting that the cytotoxicity to mammalian cells might be due to its affinity to cholesterol-containing membranes. However, membrane interactions were not completely dependent on sterols. Yeast chemogenomic profiling suggested additional direct or indirect effects on actin. Accordingly, we performed actin polymerization assays, which suggested that amantelide A also promotes actin polymerization in cell-free systems. However, the C-33 acetoxy derivative amantelide B showed a similar effect on actin dynamics in vitro but no significant activity against yeast. Overall, these studies suggest that the membrane effects are the most functionally relevant for amantelide A mechanism of action.

Disease Diagnostics and Potential Coinfections by Vibrio coralliilyticus During an Ongoing Coral Disease Outbreak in Florida

A deadly coral disease outbreak has been devastating the Florida Reef Tract since 2014. This disease, stony coral tissue loss disease (SCTLD), affects at least 22 coral species causing the progressive destruction of tissue. The etiological agents responsible for SCTLD are unidentified, but pathogenic bacteria are suspected. Virulence screens of 400 isolates identified four potentially pathogenic strains of Vibrio spp. subsequently identified as V. coralliilyticus. Strains of this species are known coral pathogens; however, cultures were unable to consistently elicit tissue loss, suggesting an opportunistic role. Using an improved immunoassay, the VcpA RapidTest, a toxic zinc-metalloprotease produced by V. coralliilyticus was detected on 22.3% of diseased Montastraea cavernosa (n = 67) and 23.5% of diseased Orbicella faveolata (n = 24). VcpA⁺ corals had significantly higher mortality rates and faster disease progression. For VcpA^- fragments, 21.6% and 33.3% of M. cavernosa and O. faveolata, respectively, died within 21 d of observation, while 100% of similarly sized VcpA⁺ fragments of both species died during the same period. Further physiological and genomic analysis found no apparent differences between the Atlantic V. coralliilyticus strains cultured here and pathogens from the Indo-Pacific but highlighted the diversity among strains and their immense genetic potential. In all, V. coralliilyticus may be causing coinfections that exacerbate existing SCTLD lesions, which could contribute to the intraspecific differences observed between colonies. This study describes potential coinfections contributing to SCTLD virulence as well as diagnostic tools capable of tracking the pathogen involved, which are important contributions to the management and understanding of SCTLD.

Dolastatin 15 from a Marine Cyanobacterium Suppresses HIF-1α Mediated Cancer Cell Viability and Vascularization

Chemical investigation of a benthic marine cyanobacterium yielded the anticancer agent dolastatin 15, originally isolated from a mollusk. Dolastatin 15 is a microtubule-destabilizing agent with analogues undergoing clinical evaluation. Profiling against a panel of isogenic HCT116 colorectal cancer cells showed remarkable differential cytotoxicity against the parental cells over isogenic cells lacking HIF or other key players in the pathway, including oncogenic KRAS and VEGF. Dolastatin 15 displayed an antivascularization effect in human endothelial cells and in zebrafish vhl mutants with activated Hif, thus signifying its clinical potential as a treatment for solid tumors with an angiogenic component. Global transcriptome analysis with RNA sequencing suggested that dolastatin 15 could affect other major cancer pathways that might not directly involve tubulin or HIF. The identification of the true producer of a clinically relevant agent is important for sustainable supply, as is understanding the biosynthesis, and future genetic manipulation of the biosynthetic gene cluster for analogue production.

Effects of future climate on coral-coral competition

As carbon dioxide (CO₂) levels increase, coral reefs and other marine systems will be affected by the joint stressors of ocean acidification (OA) and warming. The effects of these two stressors on coral physiology are relatively well studied, but their impact on biotic interactions between corals are poorly understood. While coral-coral interactions are less common on modern reefs, it is important to document the nature of these interactions to better inform restoration strategies in the face of climate change. Using a mesocosm study, we evaluated whether the combined effects of ocean acidification and warming alter the competitive interactions between the common coral Porites astreoides and two other mounding corals (Montastraea cavernosa or Orbicella faveolata) common in the Caribbean. After 7 days of direct contact, P. astreoides suppressed the photosynthetic potential of M. cavernosa by 100% in areas of contact under both present (~28.5°C and ~400 μatm pCO₂) and predicted future (~30.0°C and ~1000 μatm pCO₂) conditions. In contrast, under present conditions M. cavernosa reduced the photosynthetic potential of P. astreoides by only 38% in areas of contact, while under future conditions reduction was 100%. A similar pattern occurred between P. astreoides and O. faveolata at day 7 post contact, but by day 14, each coral had reduced the photosynthetic potential of the other by 100% at the point of contact, and O. faveolata was generating larger lesions on P. astreoides than the reverse. In the absence of competition, OA and warming did not affect the photosynthetic potential of any coral. These results suggest that OA and warming can alter the severity of initial coral-coral interactions, with potential cascading effects due to corals serving as foundation species on coral reefs.

Eudesmacarbonate, a Eudesmane-Type Sesquiterpene from a Marine Filamentous Cyanobacterial Mat (Oscillatoriales) in the Florida Keys

A new, cyclic carbonate eudesmane-type sesquiterpene, eudesmacarbonate (1), was isolated from marine filamentous cyanobacterial mats associated with apparent ingestion-related intoxications of captive bottlenose dolphins in the Florida Keys. Sequencing of 16S rDNA revealed that mats were composed of closely related Oscillatoriacean species including a previously undocumented species of Neolyngbya. The structure of 1 was elucidated by (+)-HRESIMS, 1D and 2D NMR, single-crystal X-ray diffraction, and vibrational circular dichroism data. Toxicity of 1 was assessed in the zebrafish embryo/larval model, and 1 was found to exhibit effects qualitatively similar to those observed for the known neurotoxin brevetoxin-2 and consistent with neurobehavioral impairment.

Microbial symbionts and ecological divergence of Caribbean sponges: A new perspective on an ancient association

Marine sponges host diverse communities of microbial symbionts that expand the metabolic capabilities of their host, but the abundance and structure of these communities is highly variable across sponge species. Specificity in these interactions may fuel host niche partitioning on crowded coral reefs by allowing individual sponge species to exploit unique sources of carbon and nitrogen, but this hypothesis is yet to be tested. Given the presence of high sponge biomass and the coexistence of diverse sponge species, the Caribbean Sea provides a unique system in which to investigate this hypothesis. To test for ecological divergence among sympatric Caribbean sponges and investigate whether these trends are mediated by microbial symbionts, we measured stable isotope (δ13C and δ15N) ratios and characterized the microbial community structure of sponge species at sites within four regions spanning a 1700 km latitudinal gradient. There was a low (median of 8.2 %) overlap in the isotopic niches of sympatric species; in addition, host identity accounted for over 75% of the dissimilarity in both δ13C and δ15N values and microbiome community structure among individual samples within a site. There was also a strong phylogenetic signal in both δ15N values and microbial community diversity across host phylogeny, as well as a correlation between microbial community structure and variation in δ13C and δ15N values across samples. Together, this evidence supports a hypothesis of strong evolutionary selection for ecological divergence across sponge lineages and suggests that this divergence is at least partially mediated by associations with microbial symbionts.

Discovery, Total Synthesis, and SAR of Anaenamides A and B: Anticancer Cyanobacterial Depsipeptides with a Chlorinated Pharmacophore

New modified depsipeptides and geometric isomers, termed anaenamides A (1a) and B (1b), along with the presumptive biosynthetic intermediate, anaenoic acid (2), were discovered from a marine cyanobacterium from Guam. Structures were confirmed by total synthesis. The alkylsalicylic acid fragment and the C-terminal α-chlorinated α,β-unsaturated ester are novelties in cyanobacterial natural products. Cancer cell viability assays indicated that the C-terminal unit serves as the pharmacophore and that the double-bond geometry impacts the cytotoxicity.

Seaweed natural products modify the host inflammatory response via Nrf2 signaling and alter colon microbiota composition and gene expression

Seaweeds are an important component of human diets, especially in Asia and the Pacific islands, and have shown chemopreventive as well as anti-inflammatory properties. However, structural characterization and mechanistic insight of seaweed components responsible for their biological activities are lacking. We isolated cymopol and related natural products from the marine green alga Cymopolia barbata and demonstrated their function as activators of transcription factor Nrf2-mediated antioxidant response to increase the cellular antioxidant status. We probed the reactivity of the bioactivation product of cymopol, cymopol quinone, which was able to modify various cysteine residues of Nrf2's cytoplasmic repressor protein Keap1. The observed adducts are reflective of the polypharmacology at the level of natural product, due to multiple electrophilic centers, and at the amino acid level of the cysteine-rich target protein Keap1. The non-polar C. barbata extract and its major active component cymopol, reduced inflammatory gene transcription in vitro in macrophages and mouse embryonic fibroblasts in an Nrf2-dependent manner. Cymopol-containing extracts attenuated neutrophil migration in a zebrafish tail wound model. RNA-seq analysis of colonic tissues of mice exposed to non-polar extract or cymopol showed an antioxidant and anti-inflammatory response, with more pronounced effects exhibited by the extract. Cymopolia extract reduced DSS-induced colitis as measured by fecal lipocalin concentration. RNA-seq showed that mucosal-associated bacterial composition and transcriptional profile in large intestines were beneficially altered to varying degrees in mice treated with either the extract or cymopol. We conclude that seaweed-derived compounds, especially cymopol, alter Nrf2-mediated host and microbial gene expression, thereby providing polypharmacological effects.

Promising prospects of nanopore sequencing for algal hologenomics and structural variation discovery

BACKGROUND

The MinION Access Program (MAP, 2014-2016) allowed selected users to test the prospects of long nanopore reads for diverse organisms and applications through the rapid development of improving chemistries. In 2014, faced with a fragmented Illumina assembly for the chloroplast genome of the green algal holobiont Caulerpa ashmeadii, we applied to the MAP to test the prospects of nanopore reads to investigate such intricacies, as well as further explore the hologenome of this species with native and hybrid approaches.

RESULTS

The chloroplast genome could only be resolved as a circular molecule in nanopore assemblies, which also revealed structural variants (i.e. chloroplast polymorphism or heteroplasmy). Signal and Illumina polishing of nanopore-assembled organelle genomes (chloroplast and mitochondrion) reflected the importance of coverage on final quality and current limitations. In hybrid assembly, our modest nanopore data sets showed encouraging results to improve assembly length, contiguity, repeat content, and binning of the larger nuclear and bacterial genomes. Profiling of the holobiont with nanopore or Illumina data unveiled a dominant Rhodospirillaceae (Alphaproteobacteria) species among six putative endosymbionts. While very fragmented, the cumulative hybrid assembly length of C. ashmeadii's nuclear genome reached 24.4 Mbp, including 2.1 Mbp in repeat, ranging closely with GenomeScope's estimate (> 26.3 Mbp, including 4.8 Mbp in repeat).

CONCLUSION

Our findings relying on a very modest number of nanopore R9 reads as compared to current output with newer chemistries demonstrate the promising prospects of the technology for the assembly and profiling of an algal hologenome and resolution of structural variation. The discovery of polymorphic 'chlorotypes' in C. ashmeadii, most likely mediated by homing endonucleases and/or retrohoming by reverse transcriptases, represents the first report of chloroplast heteroplasmy in the siphonous green algae. Improving contiguity of C. ashmeadii's nuclear and bacterial genomes will require deeper nanopore sequencing to greatly increase the coverage of these larger genomic compartments.

Differential gene expression during substrate probing in larvae of the Caribbean coral Porites astreoides

The transition from larva to adult is a critical step in the life history strategy of most marine animals. However, the genetic basis of this life history change remains poorly understood in many taxa, including most coral species. Recent evidence suggests that coral planula larvae undergo significant changes at the physiological and molecular levels throughout the development. To investigate this, we characterized differential gene expression (DGE) during the transition from planula to adult polyp in the abundant Caribbean reef-building coral Porites astreoides, that is from nonprobing to actively substrate-probing larva, a stage required for colony initiation. This period is crucial for the coral, because it demonstrates preparedness to locate appropriate substrata for settlement based on vital environmental cues. Through RNA-Seq, we identified 860 differentially expressed holobiont genes between probing and nonprobing larvae (p ≤ .01), the majority of which were upregulated in probing larvae. Surprisingly, differentially expressed genes of endosymbiotic dinoflagellate origin greatly outnumbered coral genes, compared with a nearly 1:1 ratio of coral-to-dinoflagellate gene representation in the holobiont transcriptome. This unanticipated result suggests that dinoflagellate endosymbionts may play a significant role in the transition from nonprobing to probing behaviour in dinoflagellate-rich larvae. Putative holobiont genes were largely involved in protein and nucleotide binding, metabolism and transport. Genes were also linked to environmental sensing and response and integral signalling pathways. Our results thus provide detailed insight into molecular changes prior to larval settlement and highlight the complex physiological and biochemical changes that occur in early transition stages from pelagic to benthic stages in corals, and perhaps more importantly, in their endosymbionts.

Chemical Ecology of Marine Sponges: New Opportunities through "-Omics"

The chemical ecology and chemical defenses of sponges have been investigated for decades; consequently, sponges are among the best understood marine organisms in terms of their chemical ecology, from the level of molecules to ecosystems. Thousands of natural products have been isolated and characterized from sponges, and although relatively few of these compounds have been studied for their ecological functions, some are known to serve as chemical defenses against predators, microorganisms, fouling organisms, and other competitors. Sponges are hosts to an exceptional diversity of microorganisms, with almost 40 microbial phyla found in these associations to date. Microbial community composition and abundance are highly variable across host taxa, with a continuum from diverse assemblages of many microbial taxa to those that are dominated by a single microbial group. Microbial communities expand the nutritional repertoire of their hosts by providing access to inorganic and dissolved sources of nutrients. Not only does this continuum of microorganism-sponge associations lead to divergent nutritional characteristics in sponges, these associated microorganisms and symbionts have long been suspected, and are now known, to biosynthesize some of the natural products found in sponges. Modern "omics" tools provide ways to study these sponge-microbe associations that would have been difficult even a decade ago. Metabolomics facilitate comparisons of sponge compounds produced within and among taxa, and metagenomics and metatranscriptomics provide tools to understand the biology of host-microbe associations and the biosynthesis of ecologically relevant natural products. These combinations of ecological, microbiological, metabolomic and genomics tools, and techniques provide unprecedented opportunities to advance sponge biology and chemical ecology across many marine ecosystems.

Microbial Community Shifts Associated With the Ongoing Stony Coral Tissue Loss Disease Outbreak on the Florida Reef Tract

As many as 22 of the 45 coral species on the Florida Reef Tract are currently affected by stony coral tissue loss disease (SCTLD). The ongoing disease outbreak was first observed in 2014 in Southeast Florida near Miami and as of early 2019 has been documented from the northernmost reaches of the reef tract in Martin County down to Key West. We examined the microbiota associated with disease lesions and apparently healthy tissue on diseased colonies of Montastraea cavernosa, Orbicella faveolata, Diploria labyrinthiformis, and Dichocoenia stokesii. Analysis of differentially abundant taxa between disease lesions and apparently healthy tissue identified five unique amplicon sequence variants enriched in the diseased tissue in three of the coral species (all except O. faveolata), namely an unclassified genus of Flavobacteriales and sequences identified as Fusibacter (Clostridiales), Planktotalea (Rhodobacterales), Algicola (Alteromonadales), and Vibrio (Vibrionales). In addition, several groups of likely opportunistic or saprophytic colonizers such as Epsilonbacteraeota, Patescibacteria, Clostridiales, Bacteroidetes, and Rhodobacterales were also enriched in SCTLD disease lesions. This work represents the first microbiological characterization of SCTLD, as an initial step toward identifying the potential pathogen(s) responsible for SCTLD.

Discovery and Total Synthesis of Doscadenamide A: A Quorum Sensing Signaling Molecule from a Marine Cyanobacterium

Quorum sensing (QS) plays a critical role in the regulation of bacterial pathogenesis. Doscadenamide A (1a) was isolated from a marine cyanobacterium, its structure elucidated by NMR, and its activity linked to QS induction. The total synthesis of 1a was developed, and the absolute configuration confirmed through comparison of the isolated natural product with synthetic diastereomers. Our preliminary investigation indicated that 1a could activate QS signaling in a LasR-dependent manner.

Mass Spectrometry-Based Integration and Expansion of the Chemical Diversity Harbored Within a Marine Sponge

Marine sponges and their associated symbionts produce a structurally diverse and complex set of natural products including alkaloids, terpenoids, peptides, lipids, and steroids. A single sponge with its symbionts can produce all of the above-mentioned classes of molecules and their analogs. Most approaches to evaluating sponge chemical diversity have focused on major metabolites that can be isolated and characterized; therefore, a comprehensive evaluation of intra- (within a molecular family; analogs) and inter-chemical diversity within a single sponge remains incomplete. We use a combination of metabolomics tools, including a supervised approach via manual library search and literature search, and an unsupervised approach via molecular networking and MS2LDA analysis to describe the intra and inter-chemical diversity present in Smenospongia aurea. Furthermore, we use imaging mass spectrometry to link this chemical diversity to either the sponge or the associated cyanobacteria. Using these approaches, we identify seven more molecular features that represent analogs of four previously known peptide/polyketide smenamides and assign the biosynthesis of these molecules to the symbiotic cyanobacteria by imaging mass spectrometry. We extend this analysis to a wide diversity of molecular classes including indole alkaloids and meroterpenes.

Discovery of Amantamide, a Selective CXCR7 Agonist from Marine Cyanobacteria

CXCR7 plays an emerging role in several physiological processes. A linear peptide, amantamide (1), was isolated from marine cyanobacteria, and the structure was determined by NMR and mass spectrometry. The total synthesis was achieved by solid-phase method. After screening two biological target libraries, 1 was identified as a selective CXCR7 agonist. The selective activation of CXCR7 by 1 could provide the basis for developing CXCR7-targeted therapeutics and deciphering the role of CXCR7 in different diseases.

Chemical and Metagenomic Studies of the Lethal Black Band Disease of Corals Reveal Two Broadly Distributed, Redox-Sensitive Mixed Polyketide/Peptide Macrocycles

Black band disease (BBD), a lethal, polymicrobial disease consortium dominated by the cyanobacterium Roseofilum reptotaenium, kills many species of corals worldwide. To uncover chemical signals or cytotoxins that could be important in proliferation of Roseofilum and the BBD layer, we examined the secondary metabolites present in geographically diverse collections of BBD from Caribbean and Pacific coral reefs. Looekeyolide A (1), a 20-membered macrocyclic compound formed by a 16-carbon polyketide chain, 2-deamino-2-hydroxymethionine, and d-leucine, and its autoxidation product looekeyolide B (2) were extracted as major compounds (∼1 mg g-1 dry wt) from more than a dozen field-collected BBD samples. Looekeyolides A and B were also produced by a nonaxenic R. reptotaenium culture under laboratory conditions at similar concentrations. R. reptotaenium genomes that were constructed from four different metagenomic data sets contained a unique nonribosomal peptide/polyketide biosynthetic cluster that is likely responsible for the biosynthesis of the looekeyolides. Looekeyolide A, which readily oxidizes to looekeyolide B, may play a biological role in reducing H2O2 and other reactive oxygen species that could occur in the BBD layer as it overgrows and destroys coral tissue.

Isolation and Characterization of Anaephenes A-C, Alkylphenols from a Filamentous Cyanobacterium ( Hormoscilla sp., Oscillatoriales)

Three related new alkylphenols, termed anaephenes A-C (1-3), containing different side chains, were isolated from an undescribed filamentous cyanobacterium (VPG 16-59) collected in Guam. Our 16S rDNA sequencing efforts indicated that VPG 16-59 is a member of the marine genus Hormoscilla (Oscillatoriales). The structures of anaephenes A-C (1-3) were elucidated by spectroscopic methods, and compounds assayed for growth inhibitory activity against prokaryotic and eukaryotic cell lines. Anaephene B (2), possessing a terminal alkyne, displayed moderate activity against Bacillus cereus and Staphylococcus aureus with MIC values of 6.1 μg/mL. While 1 and 3 showed no pronounced activity in these assays, their structural features highlight the unusual biosynthetic capacity of this cyanobacterium and warrant further study.

Spatial and temporal shifts in the diet of the barnacle Amphibalanus eburneus within a subtropical estuary

The success of many sessile invertebrates in marine benthic communities is linked to their ability to efficiently remove suspended organic matter from the surrounding water column. To investigate the diet of the barnacle Amphibalanus eburneus, a dominant suspension feeder within the Indian River Lagoon (IRL) of central Florida, we compared the stable isotopes ratios (δ¹³C and δ¹⁵N) of barnacle tissue to those of particulate organic matter (POM). Collections were carried out quarterly for a year from 29 permanent sites and at sites impacted by an Aureoumbra lagunensis bloom. δ¹³C and δ¹⁵N values of Amphibalanus eburneus varied across sites, but δ¹⁵N was more stable over time. There was a range of δ¹⁵N values of Amphibalanus eburneus tissue from 6.0‰ to 10.5‰ across sites. Because land-based sources such as sewage are generally enriched in ¹⁵N, this suggests a continuum of anthropogenic influence across sites in the IRL. Over 70% of the variation in δ¹⁵N values of Amphibalanus eburneus across sites was driven by the δ¹⁵N values of POM, supporting a generalist feeding strategy on available sources of suspended organic matter. The dominance of this generalist consumer in the IRL may be linked to its ability to consume spatially and temporally variable food resources derived from natural and anthropogenic sources, as well as Aureoumbra lagunensis cells. Generalist consumers such as Amphibalanus eburneus serve an important ecological role in this ecosystem and act as a sentinel species and recorder of local, site-specific isotopic baselines.

Uncovering cryptic diversity of Lyngbya: the new tropical marine cyanobacterial genus Dapis (Oscillatoriales)

Cyanobacteria comprise an extraordinarily diverse group of microorganisms and, as revealed by increasing molecular information, this biodiversity is even more extensive than previously estimated. In this sense, the cyanobacterial genus Lyngbya is a highly polyphyletic group composed of many unrelated taxa with morphological similarities. In this study, the new genus Dapis was erected from the genus Lyngbya, based on a combined molecular, chemical, and morphological approach. Herein, two new species of cyanobacteria are described: D. pleousa and D. pnigousa. Our analyses found these species to be widely distributed and abundant in tropical and subtropical marine habitats. Seasonally, both species have the ability to form extensive algal blooms in marine habitats: D. pleousa in shallow-water, soft bottom habitats and D. pnigousa on coral reefs below depths of 10 m. Electron microscopy showed that D. pleousa contains gas vesicles, a character not previously reported in Lyngbya. These gas vesicles, in conjunction with a mesh-like network of filaments that trap oxygen released from photosynthesis, provide this species with an unusual mechanism to disperse in coastal marine waters, allowing D. pleousa to be present in both benthic and planktonic forms. In addition, both D. pleousa and D. pnigousa contained nitrogen-fixing genes as well as bioactive secondary metabolites. Several specimens of D. pnigousa biosynthesized the secondary metabolite lyngbic acid, a molecule that has also been isolated from many other marine cyanobacteria. Dapis pleousa consistently produced the secondary metabolite malyngolide, which may provide a promising chemotaxonomic marker for this species.

Discovery, Synthesis, Pharmacological Profiling, and Biological Characterization of Brintonamides A-E, Novel Dual Protease and GPCR Modulators from a Marine Cyanobacterium

Five novel modified linear peptides named brintonamides A-E (1-5) were discovered from a marine cyanobacterial sample collected from Brinton Channel, Florida Keys. The total synthesis of 1-5 in addition to two other structurally related analogues (6 and 7) was achieved, which provided more material to allow rigorous biological evaluation and SAR studies. Compounds were subjected to cancer-focused phenotypic cell viability and migration assays and orthogonal target-based pharmacological screening platforms to identify their protease and GPCR modulatory activity profiles. The cancer related serine protease kallikrein 7 (KLK7) was inhibited to similar extents with an IC50 near 20 μM by both representative members 1 and 4, which differed in the presence or lack of the N-terminal unit. In contrast to the biochemical protease profiling study, clear SAR was observed in the functional GPCR screens, where five GPCRs in antagonist mode (CCR10, OXTR, SSTR3, TACR2) and agonist mode (CXCR7) were modulated by compounds 1-7 to varying extents. Chemokine receptor type 10 (CCR10) was potently modulated by brintonamide D (4) with an IC50 of 0.44 μM. We performed in silico modeling to understand the structural basis underlying the differences in the antagonistic activity among brintonamides toward CCR10. Because of the significance of KLK7 and CCR10 in cancer progression and metastasis, we demonstrated the ability of brintonamide D (4) at 10 μM to significantly target downstream cellular substrates of KLK7 (Dsg-2 and E-cad) in vitro and to inhibit CCL27-induced CCR10-mediated proliferation and the migration of highly invasive breast cancer cells.

A Complementary Chemical and Genomic Screening Approach for Druggable Targets in the Nrf2 Pathway and Small Molecule Inhibitors to Overcome Cancer Cell Drug Resistance

Resistance to chemotherapy is a major obstacle in the treatment of a wide array of different types of cancer. Chemotherapeutic drug resistance is achieved by cancer cells by a variety of different mechanisms, which can be either compound specific or general. An emerging mechanism for nonspecific chemotherapeutic drug resistance relies on hyperactivity of the transcription factor Nrf2. Normally Nrf2 levels are tightly regulated by the ubiquitin-proteasome system; however, mutations in genes responsible for this regulation are common in many cancer types, resulting in increased expression of Nrf2, activation of its downstream target genes, and resistance to a variety of chemotherapeutic agents. For this reason, there has been considerable interest in the discovery of small molecule inhibitors of Nrf2 capable of attenuating this resistance mechanism. To this end, we have screened two commercially available libraries of known biologically active small molecules to identify potential Nrf2 inhibitors. To increase the breadth of this screen we have also screened an RNAi library that targets the majority of the druggable genome to also identify Nrf2-inhibitor targets that are not currently targeted by small molecules. To complement the commercial chemical and genomic library screening, we screened a small collection of proprietary natural products isolated from marine cyanobacteria, which included actin targeting and uncharacterized but biologically active compounds. Through these efforts, we have identified three classes of compounds: cardiac glycosides, Stat3 inhibitors, and actin disrupting agents as Nrf2 inhibitors that are able to attenuate Nrf2 activity and synergize with chemotherapeutic agents in the non-small-cell lung cancer cell line A549. In addition, we found that grassypeptolide A exerts Nrf2 modulatory activity via a thus far uncharacterized mechanism. Moreover, we have identified a set of putative Nrf2 targets comprising the transcription factors TWIST1 and ELF4, the protein kinase NEK8, the TAK1 kinase regulator TAB1, and the dual specific phosphatase DUSP4. This study broadens the range of mechanisms through which inhibition of Nrf2 activity can be achieved, which will facilitate the characterization of novel Nrf2 inhibitors and allow the design of target specific screening procedures with which to identify more.

Discovery of new A- and B-type laxaphycins with synergistic anticancer activity

Two new cyclic lipopeptides termed laxaphycins B4 (1) and A2 (2) were discovered from a collection of the marine cyanobacterium Hormothamnion enteromorphoides, along with the known compound laxaphycin A. The planar structures were solved based on a combined interpretation of 1D and 2D NMR data and mass spectral data. The absolute configurations of the subunits were determined by chiral LC-MS analysis of the hydrolysates, advanced Marfey's analysis and 1D and 2D ROESY experiments. Consistent with similar findings on other laxaphycin A- and B-type peptides, laxaphycin B4 (1) showed antiproliferative effects against human colon cancer HCT116 cells with IC50 of 1.7 µM, while laxaphycins A and A2 (2) exhibited weak activities. The two major compounds isolated from the sample, laxaphycins A and B4, were shown to act synergistically to inhibit the growth of HCT116 colorectal cancer cells.

Structural Diversity and Anticancer Activity of Marine-Derived Elastase Inhibitors: Key Features and Mechanisms Mediating the Antimetastatic Effects in Invasive Breast Cancer

Three new 3-amino-6-hydroxy-2-piperidone (Ahp)-containing cyclic depsipeptides, named loggerpeptins A-C (1-3), along with molassamide (4), were discovered from a marine cyanobacterium, extending the structural diversity of this prevalent scaffold of cyanobacterial serine protease inhibitors. Molassamide, which contains a 2-amino-butenoic (Abu) unit in the cyclic core, was the most potent and selective analogue against human neutrophil elastase (HNE). Given the growing evidence supporting the role of HNE in breast cancer progression and metastasis, we assessed the cellular effects of compounds 3 and 4 in the context of targeting invasive breast cancer. Both compounds inhibited cleavage of the elastase substrate CD40 in biochemical assays; however, only 4 exhibited significant cellular activity. As CD40 and other receptor proteolytic processing culminates in NFκB activation, we assessed the effects of 4 on the expression of target genes, including ICAM-1. ICAM-1 is also a direct target of elastase and, in our studies, compound 4 attenuated both elastase-induced ICAM-1 gene expression and ICAM-1 proteolytic processing by elastase, revealing a potential dual effect on migration through modulation of gene expression and proteolytic processing. Molassamide also specifically inhibited the elastase-mediated migration of highly invasive triple-negative breast cancer cells.

Apratyramide, a Marine-Derived Peptidic Stimulator of VEGF-A and Other Growth Factors with Potential Application in Wound Healing

A novel linear depsipeptide enriched with tyrosine-derived moieties, termed apratyramide, was isolated from an apratoxin-producing cyanobacterium. The structure was determined using a combination of NMR spectroscopy, mass spectrometry, and chiral analysis of the acid hydrolyzate and confirmed by total synthesis. Apratyramide up-regulated multiple growth factors at the transcript level in human keratinocyte (HaCaT) cells and induced the secretion of vascular endothelial growth factor A (VEGF-A) from HaCaT cells, suggesting the compound's potential wound-healing properties through growth factor induction. Transcriptome analysis and sequential validation supported the hypothesis and indicated its mode of action (MOA) through the unfolded protein response (UPR) pathway, which is functionally related to wound healing and angiogenesis. The conditioned medium of HaCaT cells treated with apratyramide induced angiogenesis in vitro. An ex vivo rabbit corneal epithelial model was applied to confirm the VEGF-A induction in this wound-healing model.

Interspecific Variation in Coral Settlement and Fertilization Success in Response to Hydrogen Peroxide Exposure

Hydrogen peroxide (H₂O₂) is involved in the regulation of numerous reproductive and morphogenic processes across an array of taxa. Extracellular H₂O₂ can be widespread in oceanic waters, and elevated sea surface temperatures can cause increased levels of intracellular H₂O₂ within cnidarian tissue, but it remains unclear how this compound affects early life-history processes in corals, such as fertilization, metamorphosis, and settlement. To evaluate the effects of H₂O₂ on multiple stages of recruitment, experiments were conducted using Caribbean corals with various reproductive modes, including the brooders Porites astreoides and Favia fragum and the broadcast-spawning species Acropora palmata and Orbicella franksi. H₂O₂ accelerated settlement in all brooding species tested. Concentrations of 1000 µmol l^-1 H₂O₂ caused close to 100% settlement in all larval age classes, regardless of exposure duration. As larvae aged, the required threshold of H₂O₂ capable of inducing settlement decreased. In contrast, H₂O₂ concentrations of 100 µmol l^-1 or greater caused a significant reduction in metamorphosis and settlement in the larvae of spawners. Furthermore, fertilization of their gametes was inhibited in the presence of H₂O₂ concentrations as low as 100 µmol l^-1. In Porites astreoides larvae, internal levels of H₂O₂ reached a maximal value of 75 µmol l^-1 following 48 h of incubation at 31 °C. This concentration was found to significantly alter settlement rates in both brooding coral species and likely induced a cellular cascade in the settlement signaling pathway. The results of this study suggest that temperature stress influences H₂O₂ production, which in turn impacts coral settlement. While it is unlikely that the current levels of externally derived concentrations of oceanic H₂O₂ are affecting coral larvae, internal concentrations (produced under heat stress) have the capacity to impact recruitment under a changing climate.

Grassystatins D-F, Potent Aspartic Protease Inhibitors from Marine Cyanobacteria as Potential Antimetastatic Agents Targeting Invasive Breast Cancer

Three new modified peptides named grassystatins D-F (1-3) were discovered from a marine cyanobacterium from Guam. Their structures were elucidated using NMR spectroscopy and mass spectrometry. The hallmark structural feature in the peptides is a statine unit, which contributes to their aspartic protease inhibitory activity preferentially targeting cathepsins D and E. Grassystatin F (3) was the most potent analogue, with IC50 values of 50 and 0.5 nM against cathepsins D and E, respectively. The acidic tumor microenvironment is known to increase the activation of some of the lysosomal proteases associated with tumor metastasis such as cathepsins. Because cathepsin D is a biomarker in aggressive forms of breast cancer and linked to poor prognosis, the effects of cathepsin D inhibition by 1 and 3 on the downstream cellular substrates cystatin C and PAI-1 were investigated. Furthermore, the functional relevance of targeting cathepsin D substrates was evaluated by examining the effect of 1 and 3 on the migration of MDA-MD-231 cells. Grassystatin F (3) inhibited the cleavage of cystatin C and PAI-1, the activities of their downstream targets cysteine cathepsins and tPA, and the migration of the highly aggressive triple negative breast cancer cells, phenocopying the effect of siRNA-mediated knockdown of cathepsin D.

Bloom dynamics and chemical defenses of benthic cyanobacteria in the Indian River Lagoon, Florida

Cyanobacterial blooms are predicted to become more prominent in the future as a result of increasing seawater temperatures and the continued addition of nutrients to coastal waters. Many benthic marine cyanobacteria have potent chemical defenses that protect them from top down pressures and contribute to the persistence of blooms. Blooms of benthic cyanobacteria have been observed along the coast of Florida and within the Indian River Lagoon (IRL), a biodiverse estuary system that spans 250km along Florida's east coast. In this study, the cyanobacterial bloom progression at three sites within the central IRL was monitored over the course of two summers. The blooms consisted of four unique cyanobacterial species, including the recently described Okeania erythroflocculosa. The cyanobacteria produced a range of known bioactive compounds including malyngolide, lyngbyoic acid, microcolins A-B, and desacetylmicrocolin B. Ecologically-relevant assays showed that malyngolide inhibited the growth of marine fungi (Dendryphiella salina and Lindra thalassiae); microcolins A-B and desacetylmicrocolin B inhibited feeding by a generalist herbivore, the sea urchin Lytechinus variegatus; and lyngbyoic acid inhibited fungal growth and herbivore feeding. These chemical defenses likely contribute to the persistence of cyanobacterial blooms in the IRL during the summer growing period.