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Terpenoids are among the most ubiquitous and diverse secondary metabolites observed in nature. Although actinomycete bacteria are one of the primary sources of microbially derived secondary metabolites, they rarely produce compounds in this biosynthetic class. The terpenoid secondary metabolites that have been discovered from actinomycetes are often in the form of biosynthetic hybrids called hybrid isoprenoids (HIs). HIs include significant structural diversity and biological activity and thus are important targets for natural product discovery. Recent screening of marine actinomycetes has led to the discovery of a new lineage that is enriched in the production of biologically active HI secondary metabolites. These strains represent a promising resource for natural product discovery and provide unique opportunities to study the evolutionary history and ecological functions of an unusual group of secondary metabolites. [ABSTRACT FROM AUTHOR]

This article focuses on the fluorescent profiling of natural product producers. The biosynthesis of natural products has long been established as a means of regulating social interactions in both aquatic and terrestrial ecologies including aspects of chemical defense, symbiosis, parasitism, and predation. Several benthic dinoflagellates of the genus Prorocentrum synthesize okadaic acid, a potent protein phosphatase (PP) inhibitor associated with diarrheic shellfish poisoning and certain harmful algal blooms. A set of fluorescent analogues was synthesized to probe the cellular processing of PP inhibitors. For this study, a multiwell plate assay was used to determine the uptake of each natural product analogue.

Genome sequencing is rapidly changing the field of natural products research by providing opportunities to assess the biosynthetic potential of strains prior to chemical analysis or biological testing. Ready access to sequence data is driving the development of new bioinformatic tools and methods to identify the products of silent or cryptic pathways. While genome mining has fast become a useful approach to natural product discovery, it has also become clear that identifying pathways of interest is much easier than finding the associated products. This has led to bottlenecks in the discovery process that must be overcome for the potential of genomics-based natural product discovery to be fully realized. In this perspective, we address some of these challenges in the context of our work with the marine actinomycete genus Salinispora, which is proving to be a useful model with which to apply genome mining as an approach to natural product discovery. [ABSTRACT FROM AUTHOR]

The cancer-cell-cytotoxicity-guided fractionation of the acetone extracts of two cultured marine-derived Streptomyces strains belonging to the MAR4 group yielded six new napyradiomycins, compounds A-F ( 1- 6), together with three known compounds, napyradiomycins B2-B4 ( 7- 9). Napyradiomycins 1- 4 are new members of the napyradiomycin 'C-type' meroterpenoids, which possess a linear monoterpene bridge between C-7 and C-10a. Compound 4 has an additional tetrahydropyran ring fused to the phenol moiety. Compounds 5- 9 are related to the napyradiomycin 'B-type' meroterpenoids. The structures of all new compounds were assigned by interpretation of 1D and 2D NMR, MS, and other spectroscopic data. The relative configurations were assigned based upon interpretation of ROESY 2D NMR experiments. The cytotoxicity of 1- 9 against the human colon carcinoma cell line HCT-116 and their antibacterial activities against methicillin-resistant Staphylococcus aureus (MRSA) are presented. [ABSTRACT FROM AUTHOR]

Bacterial natural products remain an important source of new medicines. DNA sequencing has revealed that a majority of natural product biosynthetic gene clusters (BGCs) maintained in bacterial genomes have yet to be linked to the small molecules whose biosynthesis they encode. Efforts to discover the products of these orphan BGCs are driving the development of genome mining techniques based on the premise that many are transcriptionally silent during normal laboratory cultivation. Here, we employ comparative transcriptomics to assess BGC expression among four closely related strains of marine bacteria belonging to the genus Salinispora. The results reveal that slightly more than half of the BGCs are expressed at levels that should facilitate product detection. By comparing the expression profiles of similar gene clusters in different strains, we identified regulatory genes whose inactivation appears linked to cluster silencing. The significance of these subtle differences between expressed and silent BGCs could not have been predicted a priori and was only revealed by comparative transcriptomics. Evidence for the conservation of silent clusters among a larger number of strains for which genome sequences are available suggests they may be under different regulatory control from the expressed forms or that silencing may represent an underappreciated mechanism of gene cluster evolution. Coupling gene expression and metabolomics data established a bioinformatic link between the salinipostins and their associated BGC, while genetic manipulation established the genetic basis for this series of compounds, which were previously unknown from Salinispora pacifica. [ABSTRACT FROM AUTHOR]

Further chemical investigation of a marine-derived bacterium of the genus Streptomyces has led to the isolation of ansalactams B-D (1-3) along with the previously reported metabolite ansalactam A (4). Ansalactams B-D are significantly modified ansamycins, representing three new carbon skeletons and further illustrating the biosynthetic plasticity of the ansalactam class. Unlike ansalactam A, ansalactams B and D are penta- and hexacyclic metabolites, while ansalactam C illustrates an open polyene chain with a terminal carboxylic acid. [ABSTRACT FROM AUTHOR]

Peptide natural products show broad biological properties and are commonly produced by orthogonal ribosomal and nonribosomal pathways in prokaryotes and eukaryotes. To harvest this large and diverse resource of bioactive molecules, we introduce here natural product peptidogenomics (NPP), a new MS-guided genome-mining method that connects the chemotypes of peptide natural products to their biosynthetic gene clusters by iteratively matching de novo tandem MS (MSn) structures to genomics-based structures following biosynthetic logic. In this study, we show that NPP enabled the rapid characterization of over ten chemically diverse ribosomal and nonribosomal peptide natural products of previously unidentified composition from Streptomycete bacteria as a proof of concept to begin automating the genome-mining process. We show the identification of lantipeptides, lasso peptides, linardins, formylated peptides and lipopeptides, many of which are from well-characterized model Streptomycetes, highlighting the power of NPP in the discovery of new peptide natural products from even intensely studied organisms. [ABSTRACT FROM AUTHOR]

Two new diketopiperazine dipeptides, cyclomarazines A and B, were isolated and characterized along with the new cyclic heptapeptide cyclomarin D from the marine bacterium Salinispora arenicola CNS-205. These structurally related cyclic peptides each contain modified amino acid residues, including derivatives of N-(1,1-dimethylallyl)-tryptophan and δ-hydroxyleucine, which are common in the di- and heptapeptide series. Stable isotope incorporation studies in Streptomyces sp. CNB-982, which was first reported to produce the cyclomarin anti-inflammatory agents, illuminated the biosynthetic building blocks associated with the major metabolite cyclomarin A, signifying that this marine microbial peptide is nonribosomally derived largely from nonproteinogenic amino acid residues. DNA sequence analysis of the 5.8 Mb S. arenicola circular genome and PCR-targeted gene inactivation experiments identified the 47 kb cyclomarin/cyclomarazine biosynthetic gene cluster (cym) harboring 23 open reading frames. The cym locus is dominated by the 23 358 bp cymA, which encodes a 7-module nonribosomal peptide synthetase (NRPS) responsible for assembly of the full-length cyclomarin heptapeptides as well as the truncated cyclomarazine dipeptides. The unprecedented biosynthetic feature of the megasynthetase CymA to synthesize differently sized peptides in vivo may be triggered by the level of β oxidation of the priming tryptophan residue, which is oxidized in the cyclomarin series and unoxidized in the cyclomarazines. Biosynthesis of the N-(1,1-dimethyl-2,3-epoxypropyl)-β-hydroxytryptophan residue of cyclomarin A was further illuminated through gene inactivation experiments, which suggest that the tryptophan residue is reverse prenylated by CymD prior to release of the cyclic peptide from the CymA megasynthetase, whereas the cytochrome P450 CymV installs the epoxide group on the isoprene of cyclomarin C post-NRPS assembly. Last, the novel-amino acid residue 2-amino-3,5-dimethylhex-4-enoic acid in the cyclomarin series was shown by bioinformatics and stable isotope experiments to derive from a new pathway involving condensation of isobutyraldehyde and pyruvate followed by 5-adenosylmethionine methylation. Assembly of this unsaturated, branched amino acid is unexpectedly related to the degradation of the environmental pollutant 3-(3-hydroxyphenyl)propionic acid. [ABSTRACT FROM AUTHOR]

Ansalactams B-D exhibit weak antibacterial activity against methicillin-resistant S.aureus (MRSA). [ABSTRACT FROM AUTHOR]

The article offers information on an engineered biosynthesis of antiprotealide and other unnatural salinosporamide proteasome inhibitors. It states that antiprotealide is a low nanomolar synthetic proteasome inhibitor inspired by two β-lactone natural products in which the cyclohexenyl ring of salinosporamide A2 was substituted with the isopropyl functional group of omuralide.