Nigribactin, a novel siderophore from Vibrio nigripulchritudo, modulates Staphylococcus aureus virulence gene expression.

Staphylococcus aureus is a serious human pathogen that employs a number of virulence factors as part of its pathogenesis. The purpose of the present study was to explore marine bacteria as a source of compounds that modulate virulence gene expression in S. aureus. During the global marine Galathea 3 expedition, a strain collection was established comprising bacteria that express antimicrobial activity against Vibrio anguillarum and/or Staphylococcus aureus. Within this collection we searched colony material, culture supernatants, and cell extracts for virulence modulating activity showing that 68 out of 83 marine bacteria (affiliated with the Vibrionaceae and Pseudoalteromonas sp.) influenced expression of S. aureus hla encoding α-hemolysin toxin and/or spa encoding Protein A. The isolate that upon initial screening showed the highest degree of interference (crude ethyl acetate extract) was a Vibrio nigripulchritudo. Extraction, purification and structural elucidation revealed a novel siderophore, designated nigribactin, which induces spa transcription. The effect of nigribactin on spa expression is likely to be independent from its siderophore activity, as another potent siderophore, enterobactin, failed to influence S. aureus virulence gene expression. This study shows that marine microorganisms produce compounds with potential use in therapeutic strategies targeting virulence rather than viability of human pathogens.

Explorative solid-phase extraction (E-SPE) for accelerated microbial natural product discovery, dereplication, and purification.

Microbial natural products (NP) cover a high chemical diversity, and in consequence extracts from microorganisms are often complex to analyze and purify. A distribution analysis of calculated pK(a) values from the 34390 records in Antibase2008 revealed that within pH 2-11, 44% of all included compounds had an acidic functionality, 17% a basic functionality, and 9% both. This showed a great potential for using ion-exchange chromatography as an integral part of the separation procedure, orthogonal to the classic reversed-phase strategy. Thus, we investigated the use of an "explorative solid-phase extraction" (E-SPE) protocol using SAX, Oasis MAX, SCX, and LH-20 columns for targeted exploitation of chemical functionalities. E-SPE provides a minimum of fractions (15) for chemical and biological analyses and implicates development into a preparative scale methodology. Overall, this allows fast extract prioritization, easier dereplication, mapping of biological activities, and formulation of a purification strategy.

Isolation and NMR characterization of fumonisin B2 and a new fumonisin B6 from Aspergillus niger.

A new fumonisin, fumonisin B(6) (1), has been isolated by cation-exchange and reverse-phase chromatography, together with fumonisin B(2) (2), from stationary cultures of the fungus Aspergillus niger NRRL 326. Analysis of mass spectrometric and NMR data determined that FB(6) is a positional isomer of FB(1) and iso-FB(1), having hydroxyl functions at C3, C4, and C5. Analysis of the NMR data for FB(2) showed very similar chemical shift values when compared to an authentic Fusarium FB(2) standard, strongly indicating identical molecules despite that an absolute stereochemical assignment of FB(2) from A. niger was not possible.

Novofumigatonin, a new orthoester meroterpenoid from Aspergillus novofumigatus.

Novofumigatonin (1), a new metabolite, has been isolated from Aspergillus novofumigatus. The structure and relative stereochemistry were determined from HR ESI MS, one- and two-dimensional NMR, and single-crystal X-ray analysis. The absolute configuration was assigned using vibrational circular dichroism in combination with density functional calculations.

Bioactivity profiling using HPLC/microtiter-plate analysis: application to a New Zealand marine alga-derived fungus, Gliocladium sp.

Using HPLC/microtiter-plate-based generation of activity profiles the extract of a marine alga-derived fungus, identified as Gliocladium sp., was shown to contain the known strongly cytotoxic metabolite 4-keto-clonostachydiol (1) and also clonostachydiol (2) as well as gliotide (3), a new cyclodepsipeptide containing several D-amino acids. The absolute configuration of 1 was elucidated by reduction to 2, and two further oxidized derivatives of clonostachydiol (5, 6) were prepared and evaluated for biological activity.

Novel chemotaxonomic markers of the Alternaria infectoria species-group.

Two new structurally related metabolites, novae-zelandin A (1) and novae-zelandin B (2), as well as the novel metabolite 4Z-infectopyrone (3) were purified from extracts of filamentous fungi belonging to the Alternaria infectoria species-group. The structures were elucidated by a combination of 1D and 2D NMR spectroscopic data and MS data. 1-3 are important chemotaxonomic markers of the A. infectoria species-group and exhibit structures similar to those of known biologically active compounds, suggesting that they could be potential phytotoxins.

Identity and effects of quorum-sensing inhibitors produced by Penicillium species.

Quorum sensing (QS) communication systems are thought to afford bacteria with a mechanism to strategically cause disease. One example is Pseudomonas aeruginosa, which infects immunocompromised individuals such as cystic fibrosis patients. The authors have previously documented that blockage of the QS systems not only attenuates Ps. aeruginosa but also renders biofilms highly susceptible to treatment with conventional antibiotics. Filamentous fungi produce a battery of secondary metabolites, some of which are already in clinical use as antimicrobial drugs. Fungi coexist with bacteria but lack active immune systems, so instead rely on chemical defence mechanisms. It was speculated that some of these secondary metabolites could interfere with bacterial QS communication. During a screening of 100 extracts from 50 Penicillium species, 33 were found to produce QS inhibitory (QSI) compounds. In two cases, patulin and penicillic acid were identified as being biologically active QSI compounds. Their effect on QS-controlled gene expression in Ps. aeruginosa was verified by DNA microarray transcriptomics. Similar to previously investigated QSI compounds, patulin was found to enhance biofilm susceptibility to tobramycin treatment. Ps. aeruginosa has developed QS-dependent mechanisms that block development of the oxidative burst in PMN neutrophils. Accordingly, when the bacteria were treated with either patulin or penicillic acid, the neutrophils became activated. In a mouse pulmonary infection model, Ps. aeruginosa was more rapidly cleared from the mice that were treated with patulin compared with the placebo group.

Hesseltin A, a novel antiviral metabolite from Penicillium hesseltinei.

[structure: see text] Hesseltin A 1, a novel compound of mixed polyketide-terpenoid origins was isolated from the filamentous fungus Penicillium hesseltinei. The structure and stereochemistry were determined from extensive one- and two-dimensional NMR and mass spectral data.

Antimicrobial chlorinated bibenzyls from the liverwort Riccardia marginata.

Three new chlorinated bibenzyls 3, 4, and 5, have been isolated from the New Zealand liverwort Riccardia marginata. This is the first report of simple chlorinated bibenzyls from any natural source. Compounds 3-5 showed antimicrobial activity against Bacillus subtilis, Candida albicans, and Trichophyton mentagrophytes.