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Antimicrobial Activity of Euplotin C, the Sesquiterpene Taxonomic Marker from the Marine Ciliate Euplotes crassus. Dianella Savoia, 2004.Strains of the marine ciliate protist Euplotes crassus produce exclusive terpenoids called euplotins that play an ecological role . Among these derivatives, euplotin C is the main of four secondary metabolites isolated from cultures of this protozoon and represents the sesquiterpene taxonomic marker from E . crassus . Because different terpenoid metabolites of plant origin showed a certain antimicrobial activity, we assessed the compound euplotin C, purified by high-pressure liquid chromatography and solubilized in two solubility enhancers, against the protozoa Leishmania major and Leishmani infantum, the fungus Candida albicans, and nine strains of gram-positive and gram-negative microorganisms . An activity of euplotin C against Leishmania promastigotes was demonstrated (50% lethal doses were 4.6 or 8.1 µg/ml depending on the agent used to solubilize the compound), while the effect was less evident on Candida and nearly absent on bacteria . A nonsignificant cytotoxicity (50% lethal dose, >200 µg/ml) against the J774 cell line was observed . A leishmanicidal activity was also shown by the living, euplotin-producing cells of E . crassus cultured together with promastigotes; this activity increased with time from 10 min to 6 h of incubation . This study provides an initial rationale for the evaluation of euplotin C and other similar natural products as alternative or possibly synergistic compounds for current antiprotozoon chemotherapeutics . Effect of Substratum Surface Chemistry and Surface Energy on Attachment of Marine Bacteria and Algal Spores. Linnea K. Ista, 2004.Two series of self-assembled monolayers (SAMs) of  -substituted alkanethiolates on gold were used to systematically examine the effects of varying substratum surface chemistry and energy on the attachment of two model organisms of interest to the study of marine biofouling, the bacterium Cobetia marina (formerly Halomonas marina) and zoospores of the alga Ulva linza (formerly Enteromorpha linza) . SAMs were formed on gold-coated glass slides from solutions containing mixtures of methyl- and carboxylic acid-terminated alkanethiols and mixtures of methyl- and hydroxyl-terminated alkanethiols . C . marina attached in increasing numbers to SAMs with decreasing advancing water contact angles ( AW), in accordance with equation-of-state models of colloidal attachment . Previous studies of Ulva zoospore attachment to a series of mixed methyl- and hydroxyl-terminated SAMs showed a similar correlation between substratum
AW and zoospore attachment . When the hydrophilic component of the SAMs was changed to carboxylate, however, the profile of attachment of Ulva was significantly different, suggesting that a more complex model of interfacial energetics is required .
Purification and Characterization of a Monooxygenase Involved in the Biosynthetic Pathway of the Antitumor Drug Mithramycin. David Rodríguez, 2003.A monooxygenase encoded by the mtmOIV gene from the mithramycin gene cluster of Streptomyces argillaceus was purified 21-fold by a three-step purification procedure . This monooxygenase catalyzes the oxidative cleavage of the fourth ring of premithramycin B . The enzyme was dependent on NADPH and flavin adenine dinucleotide for activity with optimal pH at 9.5, and the Km values for NADPH and premithramycin B were 269.22 and 23.35 µM, respectively . The reaction catalyzed by MtmOIV yields two possible isomers of the same basic shortened aliphatic chain molecule . One of the reaction products showed important biological activity, thus highlighting the importance of the cleavage of the fourth ring of the aglycon for biological activity . Structural Analysis of the Peptide Pheromone Receptor PlnB, a Histidine Protein Kinase from Lactobacillus plantarum. Ola Johnsborg, 2003.Intercellular communication plays a key role in the regulation of several physiological processes in gram-positive bacteria . Cell-cell communication is often mediated by secreted inducer peptide pheromones (IPs), which upon reaching a threshold concentration in the environment specifically activate a cognate membrane-localized histidine protein kinase (HPK) . Interestingly, the majority of IP-activated HPKs fall into one distinct subfamily (HPK10) . As part of an effort to study the mechanism underlying pheromone-mediated activation of the HPK10 subfamily, the present work investigated the membrane topology of PlnB from Lactobacillus plantarum . Gene fusion experiments with Escherichia coli and Lactobacillus sakei, using alkaline phosphatase, ß-lactamase, and ß-galactosidase reporter fusions, suggested that PlnB is anchored to the cytoplasmic membrane via seven transmembrane segments . By domain switching between HPK10 members, it was demonstrated that the determinants for pheromone binding and specificity are contained within the transmembrane domain . The results also indicate that the mechanism of signal transduction, in which the final transmembrane segment apparently plays a key role, is conserved between members of the HPK10 subfamily .
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