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Bacteria are a major source of natural products that provide rich opportunities for both chemical and biological investigation. Although the vast majority of known bacterial metabolites derive from free-living organisms, increasing evidence supports the widespread existence of chemically prolific bacteria living in symbioses. A strategy based on bioinformatic prediction, symbiont cultivation, isotopic enrichment, and advanced analytics was used to characterize a unique polyketide, nosperin, from a lichen-associated Nostoc sp. cyanobacterium. The biosynthetic gene cluster and the structure of nosperin, determined from 30 μg of compound, are related to those of the pederin group previously known only from nonphotosynthetic bacteria associated with beetles and marine sponges. The presence of this natural product family in such highly dissimilar associations suggests that some bacterial metabolites may be specific to symbioses with eukaryotes and encourages exploration of other symbioses for drug discovery and better understanding of ecological interactions mediated by complex bacterial metabolites.biosynthesis | Peltigera membranacea | trans-acyltransferase polyketide synthase | 13 C nuclear magnetic resonance

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Proteasome inhibitors are rapidly evolving as potent treatment options in cancer therapy. One of the most promising drug candidates of this type is salinosporamide A from the bacterium Salinispora tropica. This marine natural product possesses a complex, densely functionalized γ-lactam-β-lactone pharmacophore, which is responsible for its irreversible binding to its target, the β subunit of the 20S proteasome. Salinosporamide A entered phase I clinical trials for the treatment of multiple myeloma only three years after its discovery. The strong biological activity and the challenging structure of this compound have fueled intense academic and industrial research in recent years, which has led to the development of more than ten syntheses, the elucidation of its biosynthetic pathway, and the generation of promising structure-activity relationships and oncological data. Salinosporamide A thus serves as an intriguing example of the successful interplay of modern drug discovery and biomedical research, medicinal chemistry and pharmacology, natural product synthesis and analysis, as well as biosynthesis and bioengineering.

Our knowledge about the gut microbiota of pigs is still scarce, despite the importance of these animals for biomedical research and agriculture. Here, we present a collection of cultured bacteria from the pig gut, including 110 species across 40 families and nine phyla. We provide taxonomic descriptions for 22 novel species and 16 genera. Meta-analysis of 16S rRNA amplicon sequence data and metagenome-assembled genomes reveal prevalent and pig-specific species within Lactobacillus, Streptococcus, Clostridium, Desulfovibrio, Enterococcus, Fusobacterium, and several new genera described in this study. Potentially interesting functions discovered in these organisms include a fucosyltransferase encoded in the genome of the novel species Clostridium porci, and prevalent gene clusters for biosynthesis of sactipeptide-like peptides. Many strains deconjugate primary bile acids in in vitro assays, and a Clostridium scindens strain produces secondary bile acids via dehydroxylation. In addition, cells of the novel species Bullifex porci are coccoidal or spherical under the culture conditions tested, in contrast with the usual helical shape of other members of the family Spirochaetaceae. The strain collection, called ‘Pig intestinal bacterial collection’ (PiBAC), is publicly available at www.dsmz.de/pibac and opens new avenues for functional studies of the pig gut microbiota.

Axially chiral biaryl compounds are frequently encountered in nature where they exhibit diverse biological properties. Many are biphenols that have C−C or C−O linkages installed by cytochrome P450 oxygenases that control the regio-and stereoselectivity of the intermolecular coupling reaction. In contrast, bipyrrolecoupling enzymology has not been observed. Marinopyrroles, produced by a marine-derived streptomycete, are the first 1,3′-bipyrrole natural products. On the basis of marinopyrrole's unusual bipyrrole structure, we explored its atropo-selective biosynthesis in Streptomyces sp. CNQ-418 in order to elucidate the N,C-bipyrrole homocoupling enzymology. Through a series of genetic experiments involving the discovery and heterologous expression of marinopyrrole biosynthesis genes, we report that two flavin-dependent halogenases catalyze the unprecedented homocoupling reaction.

The catalytic and selective construction of carbon-carbon bonds for the generation of complex molecules is one of the most important tasks in organic chemistry. This was clearly highlighted by the 2010 Nobel Prize in Chemistry, which was awarded for the development of Pd-catalyzed cross-coupling reactions. The underlying concept of cross-linking building blocks to generate molecular complexity can also be widely found in natural product biosynthesis. Impressive examples for such natural cross-coupling reactions are biosynthetic processes for the assembly of biaryl moieties in natural products--highly efficient enzymatic reactions that often achieve synthetically yet unmatched selectivities. This Minireview highlights selected examples that showcase these fascinating biotransformations.

Summary of recent advancesBacterial marine natural products are an important source of novel lead structures for drug discovery. The cytotoxic properties of many of these secondary metabolites are of particular interest for the development of new anti-cancer agents. Tremendous advances in marine molecular biology, genome sequencing, and bioinformatics have paved the way to fully exploit the biomedical potential of marine bacterial products. In addition, unique biosynthetic enzymes discovered from bacteria from the sea have begun to emerge as powerful biocatalysts in medicinal chemistry and total synthesis. The increasingly interdisciplinary field of marine natural product chemistry thus strongly impacts future developments in medicine, chemistry, and biology.