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Extracts from Streptomyces sp. S4.7 isolated from the rhizosphere of edelweiss, an alpine medicinal plant, exhibited activity against Gram-positive bacteria. LC-HRMS analyses of the extracts resulted in the detection of two unknown, structurally related lipopeptides that were assumed to be responsible for the antibiotic activity. LC-MS guided isolation and structure elucidation of viennamycins A and B (1 and 2) by HR-MS/MS, 1D and 2D NMR, and Marfey's analyses revealed them to be novel compounds, with viennamycin A containing cysteic acid, a unique feature for lipopeptides. Tests for antibacterial, antifungal, and cytotoxic activities of purified viennamycins, both with and without divalent cations, did not reveal any bioactivity, suggesting that their biological function, which could not be determined in the tests used, is atypical for lipopeptides. The genome of Streptomyces sp. S4.7 was sequenced and analyzed, revealing the viennamycin biosynthetic gene cluster. Detailed bioinformatics-based analysis of the viennamycin gene cluster allowed elucidation of the biosynthetic pathway for these lipopeptides.

The culture broth of endophytic Streptomyces sp. AB100, isolated from the shoots of medicinal plant Atropa belladonna (L.) was investigated for the presence of antibacterial compounds. After initial testing followed by bioactivity-guided fractionation, six new piperazic acid (PA)-containing congeners of two known peptides, JBIR-39 and JBIR-40, were identified by HR-MS/MS and NMR analyses. Only the dehydroxylated hexapeptidic derivatives with unusual incorporation of four PA moieties exhibited weak antibacterial activity against Gram-positive test organism Bacillus subtilis. A 16S rDNA-based phylogenetic tree of known Streptomyces spp. producing PA-containing hexapeptides isolated from different habitats and endophyte Streptomyces AB100 showed considerable diversity, suggesting that these metabolites may play an important environmental role beyond their antibacterial activity.

The fast growing genome databases provide us with a large number of so far unknown secondary metabolite biosynthetic gene clusters. A key method to study these gene clusters is their heterologous expression in an engineered host strain. Gene clusters derived from actinomycetes are usually expressed in a Streptomyces host strain to identify and investigate the corresponding compounds. However, heterologous expression is often accompanied with some challenges affecting the production rates of secondary metabolites. The first step is therefore the selection of a suitable expression vector and host strain. Once production has been established, there are several possibilities to improve compound yields either by media screens, by overexpression of regulatory or transport genes or by introduction of constitutive or inducible promoters. A surely important, but hitherto little studied factor is also the regulation of a heterologously expressed gene cluster by its host strain. This review gives a short overview on the chances and challenges provided by heterologous production of secondary metabolites in Streptomyces.

The fast growing genome databases provide us with a large number of so far unknown secondary metabolite biosynthetic gene clusters. A key method to study these gene clusters is their heterologous expression in an engineered host strain. Gene clusters derived from actinomycetes are usually expressed in a Streptomyces host strain to identify and investigate the corresponding compounds. However, heterologous expression is often accompanied with some challenges affecting the production rates of secondary metabolites. The first step is therefore the selection of a suitable expression vector and host strain. Once production has been established, there are several possibilities to improve compound yields either by media screens, by overexpression of regulatory or transport genes or by introduction of constitutive or inducible promoters. A surely important, but hitherto little studied factor is also the regulation of a heterologously expressed gene cluster by its host strain. This review gives a short overview on the chances and challenges provided by heterologous production of secondary metabolites in Streptomyces.

Understanding the regulation of a heterologously expressed gene cluster in a host organism is crucial for activation of silent gene clusters or overproduction of the corresponding natural product. In this study, Streptomyces coelicolor M512(nov-BG1) containing the novobiocin biosynthetic gene cluster from Streptomyces niveus NCIMB 11891 was chosen as a model. An improved DNA affinity capturing assay (DACA), combined with semi-quantitative mass spectrometry, was used to identify proteins binding to the promoter regions of the novobiocin gene cluster. Altogether, 2475 proteins were identified in DACA studies with the promoter regions of the pathway-specific regulators novE (PnovE) and novG (PnovG), of the biosynthetic genes novH-W (PnovH) and of the vegetative σ-factor hrdB (PhrdB) as a negative control. A restrictive classification for specific binding reduced this number to 17 proteins. Twelve of them were captured by PnovH, among them, NovG, two were captured by PnovE, and three by PnovG. Unexpectedly some well-known regulatory proteins, such as the global regulators NdgR, AdpA, SlbR, and WhiA were captured in similar intensities by all four tested promoter regions. Of the 17 promoter-specific proteins, three were studied in more detail by deletion mutagenesis and by overexpression. Two of them, BxlRSc and BxlR2Sc, could be identified as positive regulators of novobiocin production in S. coelicolor M512. Deletion of a third gene, sco0460, resulted in reduced novobiocin production, while overexpression had no effect. Furthermore, binding of BxlRSc to PnovH and to its own promoter region was confirmed via surface plasmon resonance spectroscopy.