Worms and other marine invertebrates living in soft sediments commonly produce brominated natural products that have been hypothesized to function as defenses against consumers, but this hypothesis ...has not been tested directly. When 16 species of worms from a Georgia mud flat were fed to two sympatric fishes (Fundulus heteroclitus, Leiostomus xanthurus) and a crab (Callinectes similis), 15 species (94%) were palatable to all three predators. Only the hemichordate Saccoglossus kowalevskii was unpalatable to both fishes, but even it was readily consumed by the crab. Bioassay-guided chemical investigations demonstrated that Saccoglossus kowalevskii was rejected by fishes because it contained 2,3,4-tribromopyrrole at 0.2% of worm dry mass. This is the first direct test of brominated worm metabolites as defenses against sympatric consumers. The deterrence of 2,3,4-tribromopyrrole in S. kowalevskii may explain why densities of this worm increase 40-fold during seasons when predation is high and densities of palatable worms decline sharply. To more broadly examine the effects of brominated metabolites on worm palatability, we collected from North Carolina, Georgia, and Florida 14 species reported to produce brominated metabolites. These species were fed to sympatric consumers to assess palatability and also analyzed for brominated metabolites by gas chromatography mass spectrometry (GC/MS). Nine of the fourteen species contained brominated metabolites, but only two were unpalatable. In a final test, five additional brominated metabolites produced by marine worms were added to palatable foods at natural concentrations and at up to 20× natural concentrations. None deterred feeding at natural concentrations, one was deterrent at 5-15× natural concentration, and four had no effect at even 20× natural concentration. Thus, while one worm was defended by a brominated compound, most worms containing brominated metabolites were palatable, and brominated natural products seldom functioned as chemical defenses against consumers.
The reef sponge Erylus formosus (Demospongiae: Geodiidae) from the Bahamas and southern Florida contains a suite of triterpene glycosides that, at a natural volumetric concentration, deters predation ...by the fish Thalassoma bifasciatum in laboratory assays, and a natural assemblage of reef fishes in field assays. Antifeedant metabolites were isolated by bioassay-guided fractionation of extracts of E. formosus using standard chromatographic methods and identified by nuclear magnetic resonance (NMR) spectroscopy and mass spectrometry. Included in the deterrent mixture from E. formosus collected in the Bahamas and Florida were at least 6 related triterpene glycosides possessing identical aglycones but with different sugar residues. Two additional compounds with a penasterol triterpene core (formoside, and an N-acetyl galactosamine derivative, formoside B) were found in specimens from the Bahamas but not Florida. Formoside, while being the major deterrent metabolite of E. formosus from the Bahamas, is less potent than the other triterpene glycosides on a weight per volume basis. As a mixture, the triterpene glycosides protect E. formosus from predatory reef fishes, but when these compounds were separated into fractions some failed to deter feeding at natural concentrations. As compounds of this type are beginning to be recognized as prevalent sponge metabolites, we suggest that terpene glycosides may have important ecological functions, just as a defensive role has been ascribed to similar compounds in sea stars, sea cucumbers, and terrestrial plants.
ClC chloride channels play essential roles in membrane excitability and maintenance of osmotic balance. Despite the recent crystallization of two bacterial ClC-like proteins, the gating mechanism for ...these channels remains unclear. In this study we tested scorpion venom for the presence of novel peptide inhibitors of ClC channels, which might be useful tools for dissecting the mechanisms underlying ClC channel gating. Recently, it has been shown that a peptide component of venom from the scorpion L. quinquestriatus hebraeus inhibits the CFTR chloride channel from the intracellular side. Using two-electrode voltage clamp we studied the effect of scorpion venom on ClC-0, -1, and -2, and found both dose- and voltage-dependent inhibition only of ClC-2. Comparison of voltage-dependence of inhibition by venom to that of known pore blockers revealed opposite voltage dependencies, suggesting different mechanisms of inhibition. Kinetic data show that venom induced slower activation kinetics compared to pre-venom records, suggesting that the active component(s) of venom may function as a gating modifier at ClC-2. Trypsinization abolished the inhibitory activity of venom, suggesting that the component(s) of scorpion venom that inhibits ClC-2 is a peptide.
Microbes are known to affect ecosystems and communities as decomposers, pathogens, and mutualists. However, they also may function as classic consumers and competitors with animals if they chemically ...deter larger consumers from using rich food-falls such as carrion, fruits, and seeds that can represent critical windfalls to both microbes and animals. Microbes often use chemicals (i.e., antibiotics) to compete against other microbes. Thus using chemicals against larger competitors might be expected and could redirect significant energy subsidies from upper trophic levels to the detrital pathway. When we baited traps in a coastal marine ecosystem with fresh vs. microbe-laden fish carrion, fresh carrion attracted 2.6 times as many animals per trap as microbe-laden carrion. This resulted from fresh carrion being found more frequently and from attracting more animals when found. Microbe-laden carrion was four times more likely to be uncolonized by large consumers than was fresh carrion. In the lab, the most common animal found in our traps (the stone crab Menippe mercenaria) ate fresh carrion 2.4 times more frequently than microbe-laden carrion. Bacteria-removal experiments and feeding bioassays using organic extracts of microbe-laden carrion showed that bacteria produced noxious chemicals that deterred animal consumers. Thus bacteria compete with large animal scavengers by rendering carcasses chemically repugnant. Because food-fall resources such as carrion are major food subsidies in many ecosystems, chemically mediated competition between microbes and animals could be an important, common, but underappreciated interaction within many communities.
Hyponatraemia is one of the most frequent disorders of the electrolyte metabolism. One of the causes may be also the syndrome of inadequate antidiuretic hormone secretion. The cause of increased ...production of antidiuretic hormone can be not only a pathological condition affecting the hypothalamo-pituitary system but also ectopic production of antidiuretic hormone or peptide with the same effect on the distal portion of the nephron. A classical type of malignant tumour where the syndrome of inadequate antidiuretic hormone secretion develops is small cell lung cancer. It is also known that some pharmaceutical preparations stimulate the output of antidiuretic hormone or potentiate its effect.
Pathogenic microbes can devastate populations of marine plants and animals. Yet, many sessile organisms such as seaweeds and sponges suffer remarkably low levels of microbial infection, despite ...lacking cell-based immune systems. Antimicrobial defenses of marine organisms are largely uncharacterized, although from a small number of studies it appears that chemical defenses may improve host resistance. In this study, we asked whether the common seaweed Lobophora variegata is chemically defended against potentially deleterious microorganisms. Using bioassay-guided fractionation, we isolated and characterized a 22-membered cyclic lactone, lobophorolide (1), of presumed polyketide origin, with sub-µM activity against pathogenic and saprophytic marine fungi. Deterrent concentrations of 1 were found in 46 of 51 samples collected from 10 locations in the Bahamas over a 4-year period. Lobophorolide (1) is structurally unprecedented, yet parts of the molecule are related to tolytoxin, the scytophycins, and the swinholides, macrolides previously isolated from terrestrial cyanobacteria and from marine sponges and gastropods. Until now, compounds of this structural class have not been associated with marine macrophytes. Our findings suggest that seaweeds use targeted antimicrobial chemical defense strategies and that secondary metabolites important in the ecological interactions between marine macroorganisms and microorganisms could be a promising source of novel bioactive compounds.
Monospecific blooms of phytoplankton can disrupt pelagic communities and negatively affect human health and economies. Interspecific competition may play an important role in promoting blooms, and so ...we tested (1) whether the outcome of competition between the red tide dinoflagellate Karenia brevis (ex Gymnodinium breve) and 12 co-occurring phytoplankters could be explained by allelopathic effects of compounds released by K. brevis and (2) whether waterborne, lipophilic molecules, including brevetoxins, are involved. Nine of 12 phytoplankton species were suppressed when grown with live K. brevis at bloom concentrations. K. brevis extracellular filtrates or lipophilic extracts of filtrates inhibited six of these nine species, indicating allelopathy. However, these inhibitory effects were weaker than those experienced by competitors exposed to live K. brevis. Brevetoxins at ecologically reasonable waterborne concentrations accounted for the modest inhibition by K. brevis of only one competitor, Skeletonema costatum. The addition of brevetoxins also caused significant autoinhibition, reducing the maximum concentration of K. brevis. Allelopathy is one mechanism by which K. brevis appears to exhibit competitive advantage over some sympatric phytoplankters, although unidentified compounds other than brevetoxins must be involved, in most cases. K. brevis was also susceptible to competitive exclusion by several species, including Odontella aurita and Prorocentrum minimum, known to thrive during K. brevis blooms. Although field experiments are required to assess whether allelopathy plays a fundamental role in bloom dynamics, our results indicate that allelopathy occurs widely but with species-specific consequences.
Plants are exposed to a variety of ecological threats from herbivores, pathogens, and parasites. In cases in which chemical defenses play a role in plant resistance, plants may produce a single ...molecule that inhibits a diverse array of enemies, or they may invest in a suite of deterrent compounds that each protect against specific threats. The snail Littoraria irrorata exerts substantial top-down control over smooth cordgrass Spartina alterniflora by culturing and grazing fungi on plant tissues. To combat fungal farming, S. alterniflora produces chemical defenses that inhibit fungal growth and reduce L. irrorata grazing. Guided by ecological assays, we isolated a fatty acid (α-dimorphecolic acid) from S. alterniflora that inhibited growth of Mycosphaerella sp., a marsh fungus commonly farmed by L. irrorata. Mycosphaerella sp. was more susceptible to the inhibitory effects of α-dimorphecolic acid than another farmed fungus, Phaeosphaeria spartinicola. Several phenolic compounds isolated from S. alterniflora deterred grazing by L. irrorata, of which one, the flavonoid glycoside orientin, was fully characterized. These defenses are not potent enough to completely deter fungi and snails but may slow down the negative effects caused by fungal farming. In a heavily grazed marsh, chemical defenses were constitutively expressed in S. alterniflora even after a month-long experiment in which exposure to fungi and herbivores was manipulated. Thus, S. alterniflora relies on multiple types of secondary metabolites instead of a single class of molecule to combat associated herbivores and fungi. Although α-dimorphecolic acid was not expressed in sufficient concentration on plant surfaces to prevent fungal establishment, this chemical defense may reduce fungal growth in plant tissues and increase the resistance of S. alterniflora to fungal farming.
The defining feature of the life cycle in monogonont rotifers such as Brachionus plicatilis (Muller) is alternation of asexual and sexual reproduction (mixis). Why sex is maintained in such life ...cycles is an important unsolved evolutionary question and one especially amenable to experimental analysis. Mixis is induced by a chemical signal produced by the rotifers which accumulates to threshold levels at high population densities. The chemical features of this signal were characterized using size exclusion, enzymatic degradation, protease protection assays, selective binding to anion ion exchange and C3 reversed phase HPLC columns, and the sequence of 17 N-terminal amino acids. These studies were carried out over two years beginning in 2003 using B. plicatilis Russian strain. When rotifer-conditioned medium was treated with proteinase K, its mixis-inducing ability was reduced by 70%. Proteinase K was added to medium auto-conditioned by 1 female ml-1 where typically 17% of daughters became mictic and mixis was reduced to 1%. A cocktail of protease inhibitors added to conditioned medium significantly reduced degradation of the mixis signal by natural proteases. Conditioned medium subjected to ultrafiltration retained mixis-inducing activity in the >10 kDa fraction, but the <10 kDa fraction had no significant activity. The putative mixis signal bound to an anion exchange column, eluting off at 0.72 M NaCl. These fractions were further separated on a C3 reversed phase HPLC column and mixis-inducing activity was associated with a 39 kDa protein. Seventeen amino acids from the N-terminus have strong similarity to a steroidogenesis-inducing protein isolated from human ovarian follicular fluid. The 39 kDa protein is an excellent candidate for the rotifer mixis induction signal.PUBLICATION ABSTRACT
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