Showing papers by "William Fenical published in 1992"

Defense of Ascidians and Their Conspicuous Larvae: Adult vs. Larval Chemical Defenses

Abstract: Previous investigations, focused primarily on vertebrates, have noted substantial losses of eggs and embryos to predators and questioned why selection has not more commonly resulted in the evolution of chemically defended eggs or embryos Hypotheses regarding the apparent rarity of such defenses have emphasized the potential incompatibility of actively developing tissues and toxic metabolites Alternatively, this apparent pattern could be an artifact of our greater knowledge of vertebrates, which in general show few tendencies for synthesizing defensive metabolites in either juvenile or adult stages In this study, we investigated adult and larval chemical defenses of a group of benthic marine invertebrates, the ascidians, in which the adults are often chemically rich, and we contrast our findings with what is known about chemical defenses of eggs and embryos from terrestrial and aquatic organisms Our findings suggest that there is no fundamental incompatibility of rapidly developing juvenile tissues and bioactive metabolites, and that chemically defended eggs and larval stages may be common among some taxonomic groups Ascidians are benthic invertebrates that often lack apparent physical defenses against predation, yet are common on coral reefs where predation by fishes is intense In contrast to most co—occurring invertebrates, many ascidians also release large, conspicuous larvae during daylight hours when exposure to fish predation would be highest Thus selection by predators might favor the evolution of distasteful larvae In situ observations indicate that many conspicuous ascidian larvae are distasteful to potential consumers We investigated the ability of secondary metabolites produced by taxonomically diverse ascidians from geographically distant locales to deter predation on both adults and larvae Larvae from the Caribbean ascidian Trididemnum solidum were distasteful to reef fishes, and when organic extracts of individual larvae were transferred onto eyes of freeze—dried krill (a good larval mimic in terms of size and color), these eyes were rejected by fishes while control eyes (solvent only) were readily eaten Larvae of the Indo—Pacific ascidian Sigillina cf signifera were also distasteful to coral—reef fishes and contained the unpalatable bipyrrole alkaloid tambjamine C When added to artificial foods at or below their natural mean concentrations and offered to consumers in field and laboratory feeding assays, the secondary metabolites produced by Trididemnum solidum (Caribbean Sea), Sigillina cf signifera (Indo—Pacific), and Polyandrocarpa sp (Gulf of California) significantly deterred feeding by co—occurring fishes and invertebrates Secondary metabolites produced by Trididemnum cf cyanophorum from the Caribbean Sea, Lissoclinum patella from the Indo—Pacific, and Aplidium californicum from the temperate Pacific, and the small stellate spicules common to many tropical didemnid ascidians did not significantly affect fish feeding High—pressure liquid chromatography (HPLC) analyses of six didemnin cyclic peptides in individual colonies of Trididemnum solidum from one patch reef at Little San Salvador, Bahamas found large inter—colony differences in their concentrations The mean concentration of didemnin B was more than double the concentration needed to significantly deter fish feeding in our field assays, and feeding tests with nordidemnin B showed that it deterred fish feeding across the entire range of natural concentrations HPLC analysis of the extract from a combined collection of T solidum larvae found adequate concentrations of didemnin B and nordidemnin B to account for their rejection by foraging fishes We demonstrate that taxonomically diverse ascidians from habitats characterized by intense predation pressure produce secondary metabolites that significantly reduce predation on both adults and larvae, and suggest that this defensive chemistry may be crucial in allowing the release of large, well—provisioned larvae during daylight periods when larvae have the greatest probability of using photic cues to select physically appropriate settlement sites Production of defensive secondary metabolites appears widespread among certain groups of ascidians, some of which are also known to concentrate acid and heavy metals as additional defensive strategies

Embryos of Homarus americanus are Protected by Epibiotic Bacteria

Abstract: Embryos of the American lobster, Homarus americanus, are remarkably resistant to infection by the fungus Lagenidium callinectes, a pathogen of many crustaceans. The surfaces of healthy lobster embryos are covered almost exclusively by a single, Gram-negative bacterium, which grows in a dense mosaic pattern. In culture, this bacterium produces a compound that completely inhibits the growth of the pathogenic fungus in vitro at 10 mcg/ml. Large-scale fermentation, extraction, and subsequent chromatographic purification led to the identification of the antifungal substance as 4-hydroxyphenethyl alcohol (tyrosol), an antibiotic substance known to be produced by terrestrial fungi.

Structure of asperketal B.

Abstract: 3,7,11-Trimethyl-13-oxabicyclo[8.3.0]trideca-2,6-diene-12-spiro-2' -(5',5'-dimethyltetrahydrofuran), asperketal B, C20H30O2, M(r) = 302.46, orthorhombic, P2(1)2(1)2(1), a = 10.064(1), b = 22.214(2), c = 8.330 (1) A, V = 1862.3 A3, Z = 4, Dx = 1.08 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 4.55 cm-1, F(000) = 664, T = 294 (1) K, R = 0.031, wR = 0.027 for 953 data. The backbone of the molecule is composed of a cyclodecadiene ring which is cis fused to a bicyclic ketal system. The relative configurations at C(1), C(10), C(11) and C(12) are 1S*, 10R*, 11R* and 12R*.

Structure of Asperketal B.

Abstract: 3,7,11-Trimethyl-13-oxabicyclo[8.3.0]trideca-2,6-diene-12-spiro-2' -(5',5'-dimethyltetrahydrofuran), asperketal B, C20H30O2, M(r) = 302.46, orthorhombic, P2(1)2(1)2(1), a = 10.064(1), b = 22.214(2), c = 8.330 (1) A, V = 1862.3 A3, Z = 4, Dx = 1.08 g cm-3, Cu K alpha, lambda = 1.54178 A, mu = 4.55 cm-1, F(000) = 664, T = 294 (1) K, R = 0.031, wR = 0.027 for 953 data. The backbone of the molecule is composed of a cyclodecadiene ring which is cis fused to a bicyclic ketal system. The relative configurations at C(1), C(10), C(11) and C(12) are 1S*, 10R*, 11R* and 12R*.

Antitumor-antibiotics from marine microorganisms

Abstract: altoough soil-derived bacteria, particularly those of the order Actinomycetales, are a well· studied resource for new antitumor-antibiotics, analogous comprehensive investigations of marine bacterial sources have not been u.ndertaken. In this paper, we describe preliminary studies of marine bacteria aimed at providing an overall assessment of the scope of marine microbial resources. An emphasis is placed upon developing new methods for the isolation and culture of salt-requiring microorganisms, and on developing the isolation of new compounds with potential in the treatment of infectious diseases and cancer. As the field of marine natural products chemistry matures and becomes even more effectively interfaced with drug development, new biological resources will need to be explored. A frontier in this regard are the microorganisms of the oceans which represent an immense resource, the scope of which remains to be fully understood. The term "microorganism" is all encompassing. It includes all organisms which require magnification for clear evaluation, and includes both unicellular organisms, filamentous fonns and multicellular organisms of small size. Further classifications are whether the organisms are phototrophic or chemotrophic (perform photosynthesis or chemical metabolism) or heterotrophic (require organic carbon sources) as a means of basic nutrition. Table 1 illustrates the diversity of microorganisms known from marine habitats. The variety is enormous, ranging from the primitive Archaebacteria to the Eucaryotes (algae, fungi, etc.). In the algae alone, there are at least 10 full plant Phyla known, with at least 100,000 species expected. In the other groups, the number of species can only be speculated. The large numbers of "microorganisms" in the world 's oceans indeed point to these organisms as a major resource for chemical and biomedical study. However, few marine microorganisms have been chemically-studied in detail. Problems in isolation and taxonomy, and in both small scale and mass scale cultivation have been formidable, thus far precluding comprehensive studies of these microbes. Troisième Symposium sur les substances naturelles d'interêt biologique de la région Pacifique-Asie -spirochetes (Order Spirochaetales) -gliding bacteria (Orders Cytophagales and Beggiatoales) Eucaryotes lower fungi (Class Phycomycetes) -fungi higher fungi Ascomycetes Deuteromycetes Basidiomycetes -microalgae -prolOzoa f1agellates amoebae cHiates Chemoheterotrophs Photoautotrophs -rods and cocci aerobic (Family Pseudomonadaceae) facultative (Family Vibrionaceae) anaerobic (sulfur-reducing bacteria) -endospore-forming rods and cocci -non spore-forming cocci (Family Micrococceae) -non spore-forming rods -actinomycetes (Order ActinomycetaIes) and related organisms Chemoheterotrophic Eubacteria