Discovery and Heterologous Production of New Cyclic Depsibosamycins

Streptomyces are producers of valuable secondary metabolites with unique scaffolds that perform a plethora of biological functions. Nonribosomal peptides are of special interest due to their variety and complexity. They are synthesized by nonribosomal peptide synthetases, large biosynthetic machineries that are encoded in the genome of many Streptomyces species. The identification of new peptides and the corresponding biosynthetic gene clusters is of major interest since knowledge can be used to facilitate combinatorial biosynthesis and chemical semisynthesis of natural products. The recently discovered bosamycins are linear octapeptides with an interesting 5-OMe tyrosine moiety and various modifications at the N-terminus. In this study, the new cyclic depsibosamycins B, C, and D from Streptomyces aurantiacus LU19075 were discovered. In comparison to the linear bosamycins B, C, and D, which were also produced by the strain, the cyclic depsibosamycins showed a side-chain-to-tail lactonization of serine and glycine, leading to a ring of four amino acids. In silico identification and heterologous expression of the depsibosamycin (dbm) gene cluster indicated that the cyclic peptides, rather than the linear derivatives, are the main products of the cluster

A Promiscuous Halogenase for the Derivatization of Flavonoids

Halogenation often improves the bioactive properties of natural products and is used in pharmaceutical research for the generation of new potential drug leads. High regio- and stereospecificity, simple reaction conditions and straightforward downstream processing are the main advantages of halogenation using enzymatic biocatalysts compared to chemical synthetic approaches. The identification of new promiscuous halogenases for the modification of various natural products is of great interest in modern drug discovery. In this paper, we report the identification of a new promiscuous FAD-dependent halogenase, DklH, from Frankia alni ACN14a. The identified halogenase readily modifies various flavonoid compounds, including those with well-studied biological activities. This halogenase has been demonstrated to modify not only flavones and isoflavones, but also flavonols, flavanones and flavanonols. The structural requirements for DklH substrate recognition were determined using a feeding approach. The homology model of DklH and the mechanism of substrate recognition are also proposed in this paper

Furaquinocins K and L : Novel Naphthoquinone-Based Meroterpenoids from Streptomyces sp. Je 1-369

Actinomycetes are the most prominent group of microorganisms that produce biologically active compounds. Among them, special attention is focused on bacteria in the genus Streptomyces. Streptomycetes are an important source of biologically active natural compounds that could be considered therapeutic agents. In this study, we described the identification, purification, and structure elucidation of two new naphthoquinone-based meroterpenoids, furaquinocins K and L, from Streptomyces sp. Je 1-369 strain, which was isolated from the rhizosphere soil of Juniperus excelsa (Bieb.). The main difference between furaquinocins K and L and the described furaquinocins was a modification in the polyketide naphthoquinone skeleton. In addition, the structure of furaquinocin L contained an acetylhydrazone fragment, which is quite rare for natural compounds. We also identified a furaquinocin biosynthetic gene cluster in the Je 1-369 strain, which showed similarity (60%) with the furaquinocin B biosynthetic gene cluster from Streptomyces sp. KO-3988. Furaquinocin L showed activity against Gram-positive bacteria without cytotoxic effects

Flavacol and Its Novel Derivative 3-β-Hydroxy Flavacol from Streptomyces sp. Pv 4-95 after the Expression of Heterologous AdpA

Actinomycetes are one of the main producers of biologically active compounds. However, their capabilities have not been fully evaluated due to the presence of many unexpressed silent clusters; moreover, actinomycetes can probably produce new or previously discovered natural products under certain conditions. Overexpressing the adpA gene into streptomycetes strains can unlock silent biosynthetic gene clusters. Herein, we showed that by applying this approach to Streptomyces sp. Pv 4-95 isolated from Phyllostachys viridiglaucescens rhizosphere soil, two new mass peaks were identified. NMR structure analysis identified these compounds as flavacol and a new 3-β-hydroxy flavacol derivative. We suggest that the presence of heterologous AdpA has no direct effect on the synthesis of flavacol and its derivatives in the Pv 4-95 strain. However, AdpA affects the synthesis of precursors by increasing their quantity, which then condenses into the resulting compounds

Identification and Heterologous Expression of the Albucidin Gene Cluster from the Marine Strain Streptomyces Albus Subsp. Chlorinus NRRL B-24108

Herbicides with new modes of action and safer toxicological and environmental profiles are needed to manage the evolution of weeds that are resistant to commercial herbicides. The unparalleled structural diversity of natural products makes these compounds a promising source for new herbicides. In 2009, a novel nucleoside phytotoxin, albucidin, with broad activity against grass and broadleaf weeds was isolated from a strain of Streptomyces albus subsp. chlorinus NRRL B-24108. Here, we report the identification and heterologous expression of the previously uncharacterized albucidin gene cluster. Through a series of gene inactivation experiments, a minimal set of albucidin biosynthetic genes was determined. Based on gene annotation and sequence homology, a model for albucidin biosynthesis was suggested. The presented results enable the construction of producer strains for a sustainable supply of albucidin for biological activity studies

Heterologous Expression of the Nybomycin Gene Cluster from the Marine Strain Streptomyces albus subsp. chlorinus NRRL B-24108

Streptomycetes represent an important reservoir of active secondary metabolites with potential applications in the pharmaceutical industry. The gene clusters responsible for their production are often cryptic under laboratory growth conditions. Characterization of these clusters is therefore essential for the discovery of new microbial pharmaceutical drugs. Here, we report the identification of the previously uncharacterized nybomycin gene cluster from the marine actinomycete Streptomyces albus subsp. chlorinus through its heterologous expression. Nybomycin has previously been reported to act against quinolone-resistant Staphylococcus aureus strains harboring a mutated gyrA gene but not against those with intact gyrA. The nybomycin-resistant mutants generated from quinolone-resistant mutants have been reported to be caused by a back-mutation in the gyrA gene that restores susceptibility to quinolones. On the basis of gene function assignment from bioinformatics analysis, we suggest a model for nybomycin biosynthesis

Dudomycins: New Secondary Metabolites Produced after Heterologous Expression of an Nrps Cluster from Streptomyces albus ssp. Chlorinus Nrrl B-24108

Since the 1950s, natural products of bacterial origin were systematically developed to be used as drugs with a wide range of medical applications. The available treatment options for many diseases are still not satisfying, wherefore, the discovery of new structures has not lost any of its importance. Beyond the great variety of already isolated and characterized metabolites, Streptomycetes still harbor uninvestigated gene clusters whose products can be accessed using heterologous expression in host organisms. This works presents the discovery of a set of structurally novel secondary metabolites, dudomycins A to D, through the expression of a cryptic NRPS cluster from Streptomyces albus ssp. Chlorinus NRRL B-24108 in the heterologous host strain Streptomyces albus Del14. A minimal set of genes, required for the production of dudomycins, was defined through gene inactivation experiments. This paper also proposes a model for dudomycin biosynthesis

Bonsecamin: A New Cyclic Pentapeptide Discovered through Heterologous Expression of a Cryptic Gene Cluster

The intriguing structural complexity of molecules produced by natural organisms is uncontested. Natural scaffolds serve as an important basis for the development of molecules with broad applications, e.g., therapeutics or agrochemicals. Research in recent decades has demonstrated that by means of classic metabolite extraction from microbes only a small portion of natural products can be accessed. The use of genome mining and heterologous expression approaches represents a promising way to discover new natural compounds. In this paper we report the discovery of a novel cyclic pentapeptide called bonsecamin through the heterologous expression of a cryptic NRPS gene cluster from Streptomyces albus ssp. chlorinus NRRL B-24108 in Streptomyces albus Del14. The new compound was successfully isolated and structurally characterized using NMR. The minimal set of genes required for bonsecamin production was determined through bioinformatic analysis and gene deletion experiments. A biosynthetic route leading to the production of bonsecamin is proposed in this paper

Novel Fredericamycin Variant Overproduced by a Streptomycin-Resistant Streptomyces albus subsp. chlorinus Strain

Streptomycetes are an important source of natural products potentially applicable in the pharmaceutical industry. Many of these drugs are secondary metabolites whose biosynthetic genes are very often poorly expressed under laboratory cultivation conditions. In many cases, antibiotic-resistant mutants exhibit increased production of natural drugs, which facilitates the identification and isolation of new substances. In this study, we report the induction of a type II polyketide synthase gene cluster in the marine strain Streptomyces albus subsp. chlorinus through the selection of streptomycin-resistant mutants, resulting in overproduction of the novel compound fredericamycin C2 (1). Fredericamycin C2 (1) is structurally related to the potent antitumor drug lead fredericamycin A

Complete Draft Genome Sequence of the Actinobacterium Nocardiopsis sinuspersici UTMC102 (DSM 45277T), Which Produces Serine Protease.

Tokovenko B, Rückert C, Kalinowski J, et al. Complete Draft Genome Sequence of the Actinobacterium Nocardiopsis sinuspersici UTMC102 (DSM 45277T), Which Produces Serine Protease. Genome Announc. 2017;5(20): e00362-17.The genome sequence of alkalohalophilic actinobacterium Nocardiopsis sinuspersici UTMC102 is provided. N. sinuspersici UTMC102 produces a highly active serine alkaline protease, and contains at least 11 gene clusters encoding the biosynthesis of secondary metabolites. The N. sinuspersici UTMC102 genome was assembled into a single chromosomal scaffold