Anti-predatory chemical defenses of ascidians: secondary metabolites or inorganic acids?

Both secondary metabolites and inorganic acids have been hypothesized to protect adult ascidians from predation, raising the possibility of alternative defensive strategies in these sessile, soft-bodied, benthic invertebrates. The objective of this investigation was to determine if ascidian species from the Western Atlantic have these chemical defenses against fish predators, and if so, to determine their location within the body of the ascidian. The palatability of crude organic extracts of whole ascidians, as well as the dissected tunics, viscera, and gonads (when possible) were determined at natural volumetric concentrations using laboratory feeding assays with the bluehead wrasse, Thalassoma bifasciatum. Acidified food pellets were also assayed to determine the effect of lowered pH on predation. Sixteen of the 17 species tested had deterrent organic extracts from some region of the body (Aplidium constellatum, Aplidium stellatum, Ascidia interrupta, Ascidia nigra, Botrylloides sp., Clavellina picta, Didemnum candidum, Didemnum vanderhosti, Diplosoma listerianum, Ecteinascidia turbinata, Eudistoma capsulatum, Eudistoma hepaticum, Rhopalaea abdominalis, Styela plicata, Symplegma rubra, and Trididemnum solidum). The location of the deterrent secondary metabolites was isolated in the gonad in all three solitary species, raising the possibility that these defenses are passed on to eggs or larvae. Nine ascidian species sequestered acid in their tunics (A. interrupta, A. nigra, A. stellatum, D. candidum, D. vanderhosti, E. capsulatum, E. hepaticum, R. abdominalis, and T. solidum) at levels that were effective in deterring fish predation (pH≤3.0). Only one species (Botrylloides nigrum) had neither chemical defense. Results of this study indicate that there is not a clear trade-off between the presence of secondary metabolites and inorganic acid defenses in ascidians, suggesting that these defenses are redundant, or that alternative chemical defenses may have evolved for different predators or for different stages in the life history of the ascidians producing them.     

The biosynthesis of glycopeptide antibiotics—a model for complex,non-ribosomally synthesized,peptidic secondary metabolites

Glycopeptide antibiotics are a class of widely known natural compounds produced by Actinomycetes. Vancomycin, the first member of the glycopeptide family to be discovered, was described in 1955 and used as an antibiotic soon thereafter. During the past 50 years numerous contributions on the structure, mode of action, and therapeutic features of vancomycin have been published. Recently, there has been considerable progress in elucidating the biosynthesis of glycopeptide antibiotics by combining molecular biology and analytical chemistry methods. Here, we provide an overview of the current knowledge regarding biosynthetic glycopeptide assembly.     

Role of peroxisomes in the biosynthesis and secretion of β-lactams and other secondary metabolites

Peroxisomes are eukaryotic organelles surrounded by a single bilayer membrane, containing a variety of proteins depending on the organism; they mainly perform degradation reactions of toxic metabolites (detoxification), catabolism of linear and branched-chain fatty acids, and removal of H₂O₂ (formed in some oxidative processes) by catalase. Proteins named peroxins are involved in recruiting, transporting, and introducing the peroxisomal matrix proteins into the peroxisomes. The matrix proteins contain the peroxisomal targeting signals PTS1 and/or PTS2 that are recognized by the peroxins Pex5 and Pex7, respectively. Initial evidence indicated that the penicillin biosynthetic enzyme isopenicillin N acyltransferase (IAT) of Penicillium chrysogenum is located inside peroxisomes. There is now solid evidence (based on electron microscopy and/or biochemical data) confirming that IAT and the phenylacetic acid- and fatty acid-activating enzymes are also located in peroxisomes. Similarly, the Acremonium chrysogenum CefD1 and CefD2 proteins that perform the central reactions (activation and epimerization of isopenicillin N) of the cephalosporin pathway are targeted to peroxisomes. Growing evidence supports the conclusion that some enzymes involved in the biosynthesis of mycotoxins (e.g., AK-toxin), and the biosynthesis of signaling molecules in plants (e.g., jasmonic acid or auxins) occur in peroxisomes. The high concentration of substrates (in many cases toxic to the cytoplasm) and enzymes inside the peroxisomes allows efficient synthesis of metabolites with interesting biological or pharmacological activities. This compartmentalization poses additional challenges to the cell due to the need to import the substrates into the peroxisomes and to export the final products; the transporters involved in these processes are still very poorly known. This article focuses on new aspects of the metabolic processes occurring in peroxisomes, namely the degradation and detoxification processes that lead to the biosynthesis and secretion of secondary metabolites.     

Altering environmental conditions induce shifts in simulated deep terrestrial subsurface bacterial communities—Secretion of primary and secondary metabolites

The deep terrestrial subsurface (DTS) harbours a striking diversity of microorganisms. However, systematic research on microbial metabolism, and how varying groundwater composition affects the bacterial communities and metabolites in these environments is lacking. In this study, DTS groundwater bacterial consortia from two Fennoscandian Shield sites were enriched and studied. We found that the enriched communities from the two sites consisted of distinct bacterial taxa, and alterations in the growth medium composition induced changes in cell counts. The lack of an exogenous organic carbon source (ECS) caused a notable increase in lipid metabolism in one community, while in the other, carbon starvation resulted in low overall metabolism, suggesting a dormant state. ECS supplementation increased CO₂ production and SO₄²⁻ utilisation, suggesting activation of a dissimilatory sulphate reduction pathway and sulphate-reducer-dominated total metabolism. However, both communities shared common universal metabolic features, most probably involving pathways needed for the maintenance of cell homeostasis (e.g., mevalonic acid pathway). Collectively, our findings indicate that the most important metabolites related to microbial reactions under varying growth conditions in enriched DTS communities include, but are not limited to, those linked to cell homeostasis, osmoregulation, lipid biosynthesis and degradation, dissimilatory sulphate reduction and isoprenoid production.     

The antiviral activity of cyclopentane β,β′-triketones related to secondary metabolites of higher plants

The effect of 20 cyclopentane β,β′-triketones and their sodium salts on the development of infections caused by tobacco mosaic virus (TMV) in leaves of tobacco (Nicotiana tabacum L. cv. Xanthi-nc) has been studied. It has been shown that the strongest antiviral effect is produced by sodium salts of 2-acetyl-4,7-dithio-2,3,4,5,6,7-hexahydro-1H-inden-1,3-dione, 2-acetyl-4-oxa-7-thio-2,3,4,5,6,7-hexahydro-1H-inden-1,3-dione, and 2-acetyl-4,5-didodecylthiocyclopent-4-en-1,3-dione. These compounds at a concentration of 2 mg/mL decrease the number of local TMV-induced necroses formed on inoculated tobacco leaves by 98% and have no toxic effect on leaf tissues.     

Abscisic acid metabolism —vacuolar/extravacuolar distribution of metabolites

The biotransformation of abscisic acid (ABA) was studied in cell suspension cultures of Lycopersicon esculentum. The ABA was converted by the cells to phaseic acid, nigellic acid, dihydrophaseic acid, abscisic acid--D-glucopyranosyl ester (ABA-Glc) and other ABA and phaseic acid conjugates. Investigation of their cellular distribution showed that the conjugated forms were located only in the vacuoles whereas ABA and its acidic metabolites were found mainly in the extravacuolar fractions. Our results, together with a number of studies on the increase of ABA-Glc as a response to stress, allow us to propose that ABA-Glc is irreversibly compartmented in the vacuoles of plant cells.Abbreviations ABA abscisic acid - ABA-Glc -D-glucopyranosyl ester of ABA - DPA 4-dihydrophaseic acid; nigellic acid=3-methyl-5-(1-hydroxy-2-hydroxymethyl-6-dimethyl-4-oxo-cyclohex-2-enyl)-penta-2Z, 4E-dienoic acid - PA phaseic acid     

Disruption of sscR encoding a γ-butyrolactone autoregulator receptor in Streptomyces scabies NBRC 12914 affects production of secondary metabolites

We report the cloning and sequence analysis of a gamma-butyrolactone autoregulator regulatory island that includes an sscR gene encoding the gamma-butyrolactone autoregulator receptor from Streptomyces scabies NBRC 12914, a plant pathogenic strain. gamma-Butyrolactone autoregulators trigger secondary metabolism, and sometimes morphological differentiation in the Gram-positive genus Streptomyces through binding to a specific autoregulator receptor. This gene cluster showed close similarity to other regulatory islands of Streptomyces origin that are responsible for the control of secondary metabolism. The recombinant SscR protein expressed in Escherichia coli prefers a gamma-butyrolactone autoregulator containing a long C-2 side chain and beta-hydroxyl group at the C-6 position. An inactivation experiment confirmed that this gamma-butyrolactone autoregulator receptor was involved in secondary metabolism but had no effects on the morphological differentiation. In the sscR-deleted mutant, the binding activity of the gamma-butyrolactone autoregulator was completely abolished, suggesting that its primary role is to detect the presence of an autoregulator in the environment. HPLC analysis of the culture broth showed that some peaks disappeared and new peaks that were not present in the broth of the wild-type strain appeared.     

Arundo donax—Source of musical reeds and industrial cellulose

Arundo donax has played an important role in the culture of the western world through its influence on the development of music. Reeds for woodwind musical instruments are still made from the culms, and no satisfactory substitutes have been developed. This grass has also been used as a source of cellulose for rayon and considered as a source of paper pulp.     

Cyanobacterial bioactive metabolites—A review of their chemistry and biology

Cyanobacterial blooms occur when algal densities exceed baseline population concentrations. Cyanobacteria can produce a large number of secondary metabolites. Odorous metabolites affect the smell and flavor of aquatic animals, whereas bioactive metabolites cause a range of lethal and sub-lethal effects in plants, invertebrates, and vertebrates, including humans. Herein, the bioactivity, chemistry, origin, and biosynthesis of these cyanobacterial secondary metabolites were reviewed. With recent revision of cyanobacterial taxonomy by Anagnostidis and Komárek as part of the Süβwasserflora von Mitteleuropa volumes 19(1–3), names of many cyanobacteria that produce bioactive compounds have changed, thereby confusing readers. The original and new nomenclature are included in this review to clarify the origins of cyanobacterial bioactive compounds.Due to structural similarity, the 157 known bioactive classes produced by cyanobacteria have been condensed to 55 classes. This review will provide a basis for more formal procedures to adopt a logical naming system. This review is needed for efficient management of water resources to understand, identify, and manage cyanobacterial harmful algal bloom impacts.     

Effects of the microbial secondary metabolites pyrrolnitrin, phenazine and patulin on INS-1 rat pancreatic β-cells

The effects on pancreatic β-cell viability and function of three microbial secondary metabolites pyrrolnitrin, phenazine and patulin were investigated, using the rat clonal pancreatic β-cell line, INS-1. Cells were exposed to 10-fold serial dilutions (range 0-10 μg mL(-1)) of the purified compounds for 2, 24 and 72 h. After 2 h exposure, only patulin (10 μg mL(-1)) was cytotoxic. All compounds showed significant cytotoxicity after 24 h. None of the compounds altered insulin secretion with 2 and 20 mM glucose after 2 h. However, after 24 h treatment, phenazine and pyrrolnitrin (10 and 100 ng mL(-1)) potentiated insulin production and glucose-stimulated insulin secretion, whereas patulin had no effect. Exposure (24 h) to either phenazine (100 ng mL(-1)) or pyrrolnitrin (10 ng mL(-1)) caused similar increases in the Ca(2+) content of INS-1 cells. The outward membrane current was inhibited after 24 h exposure to either phenazine (100 ng mL(-1)) or pyrrolnitrin (10 or 100 ng mL(-1)). This study presents novel data suggesting that high concentrations of pyrrolnitrin and phenazine are cytotoxic to pancreatic β-cells and thus possibly diabetogenic, whereas at lower concentrations these agents are nontoxic and may be insulinotropic. The possible role of such agents in the development of cystic fibrosis-related diabetes is discussed.     

Are tissue cultures of Peganum harmala a useful model system for studying how to manipulate the formation of secondary metabolites?

This article reviews our present knowledge on the formation of tryptophan derived secondary metabolites in tissue cultures of Peganum harmala. With the presence of -carboline alkaloids and serotonin, P. harmala contains two rather simple, interrelated biosynthetic pathways. The long term disadvantage of low and unstable productivity of P. harmala suspension culture has recently been overcome by establishing highly productive hairy root cultures. The first -carboline alkaloid biosynthetic enzymes, specific for the O-methylation of harmalol and harmol as well as for the oxidation of harmaline to harmine, have been detected in these cultures, and they should thus provide a suitable source for studying the yet unknown initial two enzymatic steps of -carboline alkaloid biosynthesis. Seedlings of P. harmala have also been successfully transformed with constructed strains of Agrobacterium, as demonstrated by the overexpression of a tryptophan decarboxylase gene from Catharanthus roseus in cultures of P. harmala. In such transgenic cultures a large overproduction of serotonin was observed. The relative simplicity of these pathways and the rather easy handling of the cultures could make P. harmala a useful and attractive model system for studying the interaction, regulation and manipulation of secondary pathways in cultured cells.Abbreviations TDC tryptophan decarboxylase - tdc gene of tryptophan decarboxylase     

Changes in DNA secondary structure afterγ-irradiation

Native calf thymus DNA was gamma-irradiated at 500 mug/ml in 0.01 M NaCl in the presence or absence of oxygen. By irradiation, an increasing amount of DNA becomes reactive with a water-soluble carbodiimide-derivative (CMEC). In the DNA sections reactive with CMEC the nucleotide strands are separated, a phenomenon previously described as radiation-induced denaturation. The dose-effect curve for the formation of denatured DNA shows an upward-bent form; a distinct oxygen effect of about 2 is observed. By a comparative study with DNA samples, degraded partially with DNAse I, it was shown that a minor part of the radiation-induced denaturation results from the formation of the radiation-induced single strand breaks, whereas the major part is a local denaturation independent of the strand breaks. In these locally denatured regions 20 to 50 nucleotide pairs are separated.