Neopyrrolomycins with broad spectrum antibacterial activity.

Three new antibiotics, neopyrrolomycins B (1), C (2), and D (3), with potent activity against Gram-positive pathogens were discovered. They exhibited MIC values < 1 microg/mL versus a number of resistant strains. The compounds were obtained from the ethyl acetate extracts of a Streptomyces sp. after purification by column chromatography and RP-HPLC. Their structures were elucidated using X-ray crystallography (1) and NMR spectroscopy (2 and 3).

Citreamicins with potent gram-positive activity.

Two new xanthone antibiotics, citreamicin delta (1) and epsilon (2), with potent activity against Gram-positive pathogens including multidrug-resistant Staphylococcus aureus (MDRSA) were discovered. Compounds 1 and 2 exhibited MIC values < 1 microg/mL versus a number of resistant strains. The compounds were obtained from EtOAc extracts of Streptomyces vinaceus and were purified by countercurrent chromatography and reversed-phase HPLC. Their structures were elucidated using primarily NMR and mass spectroscopy.

Mutactimycin E, a new anthracycline antibiotic with gram-positive activity.

Resistance to currently available antibiotics has become a widely recognized crisis in the medical community. To address this, many companies and researchers are refocusing their attention towards natural products, which have an excellent track record of producing effective antibacterial drugs. The AMRI natural product library was screened for activity against multi-drug resistant Staphylococcus aureus (MDRSA). The active samples were counter screened for cytotoxicity against the human hepatocellular carcinoma HepG2 cell line to determine an in vitro therapeutic index (in vitro TI). Those samples with a high in vitro TI were selected for fractionation and dereplication. This led to the discovery of a new anthracycline structure. This metabolite, named mutactimycin E (1), exhibited moderate activity against several gram positive organisms. Here we report the isolation, structure elucidation and biological activities of this new compound.

Picobiliphytes: a marine picoplanktonic algal group with unknown affinities to other eukaryotes.

Environmental sequencing has revealed unimagined diversity among eukaryotic picoplankton. A distinct picoplanktonic algal group, initially detected from 18S ribosomal DNA (rDNA) sequences, was hybridized with rRNA-targeted probes, detected by tyramide signal amplification-fluorescent in situ hybridization, and showed an organelle-like body with orange fluorescence indicative of phycobilins. Using this fluorescence signal, cells were sorted by flow cytometry and probed. Hybridized cells contained a 4',6'-diamidino-2-phenylindole-stained organelle resembling a plastid with a nucleomorph. This suggests that they may be secondary endosymbiotic algae. Pending the isolation of living cells and their formal description, these algae have been termed picobiliphytes.

Diversity of picoplanktonic prasinophytes assessed by direct nuclear SSU rDNA sequencing of environmental samples and novel isolates retrieved from oceanic and coastal marine ecosystems.

Picoplanktonic prasinophytes are well represented in culture collections and marine samples. In order to better characterize this ecologically important group, we compared the phylogenetic diversity of picoplanktonic prasinophyte strains available at the Roscoff Culture Collection (RCC) and that of nuclear SSU rDNA sequences from environmental clone libraries obtained from oceanic and coastal ecosystems. Among the 570 strains avalaible, 91 belonged to prasinophytes, 65 were partially sequenced, and we obtained the entire SSU rDNA sequence for a selection of 14 strains. Within the 18 available environmental clone libraries, the prasinophytes accounted for 12% of the total number of clones retrieved (142 partial sequences in total), and we selected 9 clones to obtain entire SSU rDNA sequence. Using this approach, we obtained a subsequent genetic database that revealed the presence of seven independent lineages among prasinophytes, including a novel clade (clade VII). This new clade groups the genus Picocystis, two unidentified coccoid strains, and 4 environmental sequences. For each of these seven lineages, at least one representative is available in culture. The three picoplanktonic genera Ostreococcus, Micromonas, and Bathycoccus (order Mamiellales), were the best represented prasinophytes both in cultures and genetic libraries. SSU rDNA phylogenetic analyses suggest that the genus Bathycoccus forms a very homogeneous group. In contrast, the genera Micromonas and Ostreococcus turned out to be quite complex, consisting of three and four independent lineages, respectively. This report of the overall diversity of picoeukaryotic prasinophytes reveals a group of ecologically important and diverse marine microorganims that are well represented by isolated cultures.

Phylogenetic and ecological analysis of novel marine stramenopiles.

Culture-independent molecular analyses of open-sea microorganisms have revealed the existence and apparent abundance of novel eukaryotic lineages, opening new avenues for phylogenetic, evolutionary, and ecological research. Novel marine stramenopiles, identified by 18S ribosomal DNA sequences within the basal part of the stramenopile radiation but unrelated to any previously known group, constituted one of the most important novel lineages in these open-sea samples. Here we carry out a comparative analysis of novel stramenopiles, including new sequences from coastal genetic libraries presented here and sequences from recent reports from the open ocean and marine anoxic sites. Novel stramenopiles were found in all major habitats, generally accounting for a significant proportion of clones in genetic libraries. Phylogenetic analyses indicated the existence of 12 independent clusters. Some of these were restricted to anoxic or deep-sea environments, but the majority were typical components of coastal and open-sea waters. We specifically identified four clusters that were well represented in most marine surface waters (together they accounted for 74% of the novel stramenopile clones) and are the obvious targets for future research. Many sequences were retrieved from geographically distant regions, indicating that some organisms were cosmopolitan. Our study expands our knowledge on the phylogenetic diversity and distribution of novel marine stramenopiles and confirms that they are fundamental members of the marine eukaryotic picoplankton.