No abstract

In 2011, the Indian River Lagoon, a biodiverse estuary in eastern Florida (USA), experienced an intense microalgal bloom with disastrous ecological consequences. The bloom included a mix of microalgae with unresolved taxonomy and lasted for 7 months with a maximum concentration of 130 μg chlorophyll a L−1. In 2012, brown tide Aureoumbra lagunensis also bloomed in portions of this estuary, with reoccurrences in 2016 and 2018. To identify and understand the role of grazer pressure (top-down control) on bloom formation, we coupled DNA sequencing with bivalve feeding assays using three microalgae isolated from the 2011 bloom and maintained in culture. Feeding experiments were conducted on widely distributed bivalve species in the lagoon, including eastern oysters (Crassostrea virginica), hooked mussels (Ischadium recurvum), charru mussels (Mytella charruana), green mussels (Perna viridis), Atlantic rangia (Rangia cuneata), and hard clams (Mercenaria mercenaria), which were exposed to 3 × 104 cells mL−1 of five species of microalgae consisting of A. lagunensis and the three species clarified herein, the picocyanobacteria Crocosphaera sp. and ‘Synechococcus’ sp., and the picochlorophyte Picochlorum sp., as well as Nannochloropsis oculata used as a control. To ensure clearance rates were indicative of consumption and assimilation, the microalgae were isotopically (15N) labeled prior to feeding experiments. Clearance rates differed among bivalve and microalgal species, but enriched 15N values in bivalve tissue suggest that algal bloom species were assimilated by the bivalves. These results expand our understanding of the important ecosystem services that healthy, biodiverse filter feeder communities provide.

A new, cyclic carbonate eudesmane-type sesquiterpene, eudesmacarbonate (1), was isolated from marine filamentous cyanobacterial mats associated with apparent ingestionrelated 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.

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.

The present investigation tests the effects against feeding by fishes of crude extracts obtained from eleven distinct populations of the bryozoan Amathia verticillata, an invasive species found globally in tropical to warm-temperate waters. Investigation of extracts from 11 populations of A. verticillata led to the identification and quantification of the known indole alkaloid 2,5,6-tribromo-N-methylgramine and isolation and identification of the new indole alkaloid, 2,6-dibromo-N-methylgramine. One extract of A. verticillata from Brazil significantly deterred feeding, while other extracts of A. verticillata from Florida significantly stimulated feeding by fishes, in field assays performed in Brazil. The same extracts of Florida samples showed variable effects on feeding, ranging from attraction to deterrence, in assays carried out in Florida. The absence of broad chemical defenses against feeding by fish suggests that the establishment of A. verticillata as an invasive species into new areas may be due to reasons other than defensive chemistry.

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.