Catalina Arévalo-Ferro

Cembranoid diterpenes from the Caribbean sea whip Eunicea knighti.

Three new cembranoid diterpenes, knightol (1), knightol acetate (2), and knightal (3), along with the known asperdiol (4) and asperdiol acetate (5), were isolated as major compounds from the sea whip Eunicea knighti collected from the Colombian Caribbean. The structures and absolute configurations of 1-5 were determined on the basis of spectroscopic analyses and by a combination of chemical and NMR methods, multiple correlations observed in a ROESY experiment, and using the modified Mosher method. Additionally, five semisynthetic compounds, 6-10, obtained during the chemical transformations of the natural compounds are here reported for the first time. All compounds were tested for antimicrobial activity against marine bacteria associated with heavily fouled surfaces and were also screened for antiquorum sensing (QS) activity. Compounds 1, 3, and 8 showed significant antimicrobial activity against bacterial isolates, and 1, 3, 7, and 8 showed excellent anti-QS inhibition activity measured by means of bioluminescence inhibition with biosensor model systems.

Glycosylflavonoids from Cecropia pachystachya Trécul are quorum sensing inhibitors.

The Cecropia genus is widely distributed in Latin America including at least 60 species, and some of them are commonly used in traditional medicine for the treatment of several diseases. We used Cecropia pachystachya Trécul to search for quorum sensing (QS) inhibitors compounds and found that the aqueous extract of C. pachystachya leaves is a promising source of substances with this activity. Using as biosensor Chromobacterium violaceum ATCC 31532 and Escherichia coli pSB403, the compounds chlorogenic acid (2), isoorientin (3), orientin (4), isovitexin (6), vitexin (7), and rutin (9) were identified as QS inhibitors. None of these compounds inhibited the growth of neither the used biosensors nor the microorganisms Staphylococcus aureus ATCC 23591, Escherichia coli ATCC 25922 and Saccharomyces cerevisiae, used here as growth inhibition controls. Along with the rutin, here we presented for the first time the QS-inhibition potential of the C-glycosyl flavonoids. The prospective of this evidence lead to the use of these compounds as antipathogenic drugs or antifoulants.

Antifouling Activities against Colonizer Marine Bacteria of Extracts from Marine Invertebrates Collected in the Colombian Caribbean Sea and on the Brazilian Coast (Santa Catarina)

The growth inhibition of 12 native marine bacteria isolated from Aplysina sponge surfaces, the shell of a bivalve, and Phytagel™ immersed for 48 h in sea water were used as indicator of the antifouling activity of the extracts of 39 marine organisms (octocorals, sponges, algae, and zoanthid) collected in the Colombian Caribbean Sea and on the Brazilian coast (Santa Catarina). Gram-negative bacteria represented 75% of the isolates; identified strains belonged to Oceanobacillus iheyensis, Ochrobactrum pseudogrignonense, Vibrio campbellii, Vibrio harveyi, and Bacillus megaterium species and seven strains were classified at genus level by the 16S rRNA sequencing method. The extracts of the octocorals Pseudopterogorgia elisabethae, four Eunicea octocorals, and the sponges Topsentia ophiraphidites, Agelas citrina, Neopetrosia carbonaria, Monanchora arbuscula, Cliona tenuis, Iotrochota imminuta, and Ptilocaulis walpersii were the most active, thus suggesting those species as antifoulant producers. This is the first study of natural antifoulants from marine organisms collected on the Colombian and Brazilian coasts.

Possible Ecological Role of Pseudopterosins G and P-U and SECO-Pseudopterosins J and K from the Gorgonian Pseudopterogorgia elisabethae from Providencia Island (SW Caribbean) in Regulating Microbial Surface Communities

The gorgonian Pseudopterogorgia elisabethae collected at Providencia Island (Colombia) has an unfouled surface, free of obvious algal and invertebrate growth. This gorgonian produces significant amounts of the glycosilated diterpenes pseudopterosins and seco-pseudopterosins (Ps and seco-Ps). Our previous experiments have shown activity of these compounds against eukaryotic (human cancer cell lines and Candida albicans) and prokaryotic cells (Staphylococcus aureus and Enterococcus faecalis). However, the potential role of pseudopterosins on the regulation of the fouling process is still under study. We evaluated the activity of these compounds against bacteria isolated from heavily fouled marine surfaces as an indicator of antifouling activity. Additionally, we assessed their activity against bacteria isolated from P. elisabethae to determine whether potentially they play a role in preventing surface bacterial colonization, thus impairing presumptively the establishment of further successional stages of fouling communities. Results showed that Ps and seco-Ps seem to modulate bacterial growth (controlling Gram-positive bacterial growth and inducing Gram-negative bacterial associations). We thus hypothesized that Ps and seco-Ps may play a role in controlling microbial fouling communities on the surface of this gorgonian. By using bTEFAP and FISH we showed that the most abundant bacteria present in the microbial communities associated with P. elisabethae are Gram-negative bacteria, with Proteobacteria and Gammaproteobacteria the most representative. To evaluate whether Ps and seco-Ps have a direct effect on the structure of the bacterial community associated with P. elisabethae, we tested these compounds against culturable bacteria associated with the surface of P. elisabethae, finding remarkable selectivity against Gram-positive bacteria. The evidence presented here suggests that Ps and seco-Ps might have a role in the selection of organisms associated with the gorgonian surface and in the regulation of the associated bacterial community composition.

Bacterial Sensors in Microfouling Assays

A lot of the marine invertebrates have a planktonic larval stage, in this period the larvae are dispersed and transported by currents. When larvae mature and attain the ability to meta‐ morphose, they start looking for suitable substrates, swimming toward the bottom and ex‐ ploring the surfaces. When larvae encounter suitable substrate, they settle and metamorphose into juveniles; the survival of them is heavily dependent on where they set‐ tle. On the other hand, larval settlement and metamorphosis are influenced by local factors as salinity, temperature, light, kind of substrates, larval age, and nutritional conditions of larvae. However, one of the most important factors for settlement is the presence of chemi‐ cal tracks originated from nonspecific adults and prey organisms. Microbial films are in‐ cluded also in those kinds of tracks and induce differentially larval settlement and metamorphosis in many invertebrate species; unfortunately, these bacterial biofilm factors have not been fully characterized [1]. The first biofilm formed on a surface, the settlement and the following steps of biological colonization are known as fouling, which could be de‐ fined (since an industrial point of view) as the undesirable accumulation of dissolved chemi‐ cal compounds, microorganisms, algae and animals on submerged substrates leading to subsequent bio-deterioration of the colonized surface.

Gas Chromathography as a Tool in Quorum Sensing Studies

Since cell differentiation was studied cell-to-cell signaling and cell regulated cycles were considered exclusive of eukaryotic organisms, prokaryotic organisms were regarded as isolated cells without cooperative behaviors. It took us more than 30 years, after Nealson et al., (1970) explained bioluminescence as an auto-induced regulated mechanism of bacterial groups, to assume in microbiology research that bacteria can synchronize group behaviors. In consequence, it was possible to explain that inter-cell signaling regulates some bacterial phenotypes and this phenomenon was called Quorum Sensing (QS). QS is one of the most revolutionary mechanisms discovered in the past 15 years. It involves the cell control of bacterial population by communication using chemical signals and a complex network of genetic circuits with a positive feedback regulation (for review see: Waters et al., 2005). Sensing these chemical signals bacteria can respond as groups and detect the “quorum” of a population in order to regulate different phenotypes.

Antiherpes screening of marine organisms from Colombian Caribbean Sea

The exploration of marine environment represents a promising strategy in the search for new active antiviral compounds. The isolation and characterization of the nucleosides spongothymidine and spongouridine from the sponge Cryptotethia crypta used as models for the synthesis of ara-A (vidarabine), that has been used therapeutically against herpetic encephalitis, was the most important contribution since the late 1970s. This paper describes the in vitro antiviral evaluation of 26 organic extracts obtained from eleven octocoral species and fifteen marine sponges. Cytotoxicity was evaluated on Vero cells by MTT assay and the antiviral activity was tested against Herpes Simplex Virus type 1 (HSV-1, KOS strain) by plaque number reduction assay. Results were expressed as 50% cytotoxic (CC50) and 50% inhibitory (IC50) concentrations, respectively, in order to calculate the selectivity index (SI= CC50/IC50) of each extract. Among the tested marine octocoral species, only three extracts showed antiviral activity, but with low selectivity indices (<3.0). Among the tested marine sponges, eight extracts showed SI values higher than 2.0, and three can be considered promising (Aka cachacrouense, Niphates erecta and Dragmacidon reticulatum) with SI values of 5.0, 8.0 and 11.7, respectively, meriting complementary studies in order to identify the bioactive components of these sponge extracts, which are in course now.