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Cloning and engineering of natural product biosynthetic pathways followed by heterologous expression in a tractable host is a widely used approach for expression and genetic modification of microbial secondary metabolites. Herein, we employed ccdB counterselection combined with oligonucleotide-mediated recombineering to efficiently create point mutations in a complex nonribosomal peptide synthetase (NRPS) from Photorabdus luminescens directing the biosynthesis of luminmides. After in depth analysis of the luminmide production profile from the native NRPS, single and double point mutations were rationally constructed within the adenylation (A) domain from NRPS module 3 which turned out to have a broad substrate tolerance. Expression of mutated versions of the 15.6 kb NRPS gene plu3263 in E. coli led to alterations in luminmide production profiles and allowed to direct the biosynthesis towards certain derivatives. These results demonstrate the suitability of counterselection recombineering for site-directed mutagenesis of complex expression constructs, e.g., genes encoding NRPS biosynthetic pathways in multi-copy plasmids.

Two new cyclic peptides, named jahnellamides A and B are isolated from the title myxobacterium.

Biological, biochemical, and structural studies presented in this paper show Chrysophaentin A (Ia) is the most potent of the isolated antibiotics, inhibited the growth of clinically relevant Gram-positive bacteria including methicillin-resistant Staphylococcus aureus, multidrug-resistant S.

The highly N-methylated linear polypeptides koshikamide C-E and the cyclic analogues F-H are isolated from Theonella swinhoei and Theonella cupola.

Seven new antibacterials, motualevic acids A−F (1−6) and (4E)-(R)-antazirine (7), have been isolated from the marine sponge Siliquariaspongia sp. and their structures elucidated by spectroscopic methods. Motualevic acids A−D are the first glycyl conjugates of the ω-brominated lipid (E)-14,14-dibromotetradeca-2,13-dienoic acid, and motualevic acid F is the first long-chain 2H-azirine 2-carboxylic acid to be found in nature. Carboxylic acid-containing compounds 1 and 6 inhibit the growth of Staphylococcus aureus and methicillin-resistant S. aureus at 1.2−10.9 μg/mL.

Six new depsipeptides belonging to two different structural classes, termed celebesides A-C and theopapuamides B-D, have been isolated from the marine sponge Siliquariaspongia mirabilis. Their structures were determined using extensive 2D NMR and ESI-MS/MS techniques. Celebesides are unusual cyclic depsipeptides that comprise a polyketide moiety and five amino acid residues, including an uncommon 3-carbamoyl threonine, and a phosphoserine residue in celebesides A and B. Theopapuamides B-D are undecapeptides with an N-terminal fatty acid moiety containing two previously unreported amino acids, 3-acetamido-2-aminopropanoic acid and 4-amino-2,3-dihydroxy-5-methylhexanoic acid. The relative configuration of the polyketide moiety in celebesides was resolved by J-based analysis and quantum mechanical calculations, the results of which were self consistent. Celebeside A neutralized HIV-1 in a single round infectivity assay with an IC50 value of 1.9 ± 0.4 μg/mL while the non-phosphorylated analog celebeside C was inactive at concentrations as high as 50 μg/mL. Theopapuamides A-C showed cytotoxicity against human colon carcinoma (HCT-116) cells with IC50 values between 2.1 and 4.0 μg/mL, and exhibited strong antifungal activity against wildtype and amphotericin B-resistant strains of Candida albicans at loads of 1-5 μg/disk.

Argeloside A and B, two novel 14,15-secopregnane glycosides characterized by the presence of two hemiketal functions involved in two five-membered rings, were isolated from Solenostemma argel fruits. Their structures have been established by ESIMS and NMR experiments. In particular the relative configuration of the molecules has been defined by combining the available NMR data with quantum chemical calculations of the geometries and 13 C chemical shifts.