Complete genome sequence of Streptomyces venezuelae ATCC 15439, a promising cell factory for production of secondary metabolites

Systems metabolic engineering of Streptomyces venezuelae for the enhanced production of pikromycin

Pikromycin is an important precursor of drugs, for example, erythromycin. Hence, systems metabolic engineering for the enhanced pikromycin production can contribute to the development of pikromycin-related drugs. In this study, metabolic genes in Streptomyces venezuelae were systematically engineered for the enhanced pikromycin production. For this, a genome-scale metabolic model of S. venezuelae was reconstructed and simulated, which led to the selection of 11 metabolic gene targets. These metabolic genes, including four overexpression targets and seven knockdown targets, were individually engineered first. Next, two overexpression targets and two knockdown targets were selected based on the 11 strains' production performances in order to engineer two to four of these genes together for the potential synergistic effects on the pikromycin production. As a result, the NM1 strain with AQF52_RS24510 (methenyltetrahydrofolate cyclohydrolase/methylenetetrahydrofolate dehydrogenase) overexpression and AQF52_RS30320 (sulfite reductase) knockdown showed the best production performance among all the 22 strains constructed in this study. Fed-batch fermentation of the NM1 strain produced 295.25 mg/L of pikromycin, by far the best production titer using the native producer S. venezuelae, to the best of our knowledge. The systems metabolic engineering strategy demonstrated herein can also be applied to the overproduction of other secondary metabolites using S. venezuelae. This article is protected by copyright. All rights reserved.

Biochemical characterization of an inverting S/O-HexNAc-transferase and evidence of S-linked glycosylation in Actinobacteria

Antimicrobial peptides harboring S- and or O-linked glycans are known as glycocins. Glycocins were first discovered and best characterized in Firmicutes. S-glycosylation is an enzymatic process catalyzed by S-glycosyltransferases of the GT2 family. Using a heterologous expression system, here we describe an inverting S/O-HexNAc-transferase (SvGT), encoded by ORF AQF52_3101 of S. venezuelae ATCC 15439, along with its acceptor substrate (SvC), encoded by ORF AQF52_3099. Using in vitro and in vivo assays, we define the distinct donor specificity, acceptor specificity, regioselectivity, chemoselectivity, and Y(G/A/K/Q/E ≠ ΔG)(C/S/T ≠ Y/N)(G/A ≠ P/Q)G as the minimum acceptor sequon of SvGT. Although UDP-GlcNAc served as the donor in the cellular milieu, SvGT could also utilize UDP-Glc and UDP-GalNAc as donors in vitro. Using mass spectrometry and western blotting, we provide evidence that an anti-O-GlcNAc antibody (CTD110.6) cross-reacts with S-GlcNAc and may be used to detect S-GlcNAcylated glycoconjugates directly. With an understanding of enzyme specificities, we finally employed SvGT to generate two proof-of-concept neoglycocins against L. monocytogenes. In conclusion, this study provides the first experimental evidence for S-glycosylation in Actinobacteria and the application of its S/O-HexNAc-transferase in glycocin engineering.

Anticancer Drug Discovery from Microbial Sources: The Unique Mangrove Streptomycetes

Worldwide cancer incidence and mortality have always been a concern to the community. The cancer mortality rate has generally declined over the years; however, there is still an increased mortality rate in poorer countries that receives considerable attention from healthcare professionals. This suggested the importance of the prompt detection, effective treatment, and prevention strategies. The genus Streptomyces has been documented as a prolific producer of biologically active secondary metabolites. Streptomycetes from mangrove environments attract researchers' attention due to their ability to synthesize diverse, interesting bioactive metabolites. The present review highlights research on mangrove-derived streptomycetes and the production of anticancer-related compounds from these microorganisms. Research studies conducted between 2008 and 2019, specifically mentioning the isolation of streptomycetes from mangrove areas and described the successful purification of compound(s) or generation of crude extracts with cytotoxic activity against human cancer cell lines, were compiled in this review. It is anticipated that there will be an increase in prospects for mangrove-derived streptomycetes as one of the natural resources for the isolation of chemotherapeutic agents.

Antibacterial properties of main-chain cationic polymers prepared through amine-epoxy 'Click' polymerization

Poly(β-hydroxyl amine)s are prepared through an amine-epoxy 'click' polymerization process in water under ambient conditions. These materials could be subjected to a post-polymerization protonation/alkylation reaction at the nitrogen atom to yield quaternary ammonium salts in the polymer backbone. The antimicrobial activities indicated that polymers carrying butyl chains at the nitrogen atom are effective towards Escherichia coli (E. coli) and Staphylococcus aureus (S. aureus), as only 10-20 μg mL-1 polymer concentrations are required to inhibit the bacterial growth by >90%. One of the candidates was also found to be effective towards Mycobacterium smegmatis (M. smegmatis) - a model organism to develop drugs against rapidly spreading tuberculosis (TB) infections. The hemolysis assay indicated that a majority of antimicrobial agents did not disrupt red blood cell membranes. The mechanistic studies suggested that cell wall disruption by the cationic polymers was the likely cause of bacterial death.

Lysine acetylation of the housekeeping sigma factor enhances the activity of the RNA polymerase holoenzyme

Protein lysine acetylation, one of the most abundant post-translational modifications in eukaryotes, occurs in prokaryotes as well. Despite the evidence of lysine acetylation in bacterial RNA polymerases (RNAPs), its function remains unknown. We found that the housekeeping sigma factor (HrdB) was acetylated throughout the growth of an actinobacterium, Streptomyces venezuelae, and the acetylated HrdB was enriched in the RNAP holoenzyme complex. The lysine (K259) located between 1.2 and 2 regions of the sigma factor, was determined to be the acetylated residue of HrdB in vivo by LC–MS/MS analyses. Specifically, the label-free quantitative analysis revealed that the K259 residues of all the HrdB subunits were acetylated in the RNAP holoenzyme. Using mutations that mimic or block acetylation (K259Q and K259R), we found that K259 acetylation enhances the interaction of HrdB with the RNAP core enzyme as well as the binding activity of the RNAP holoenzyme to target promoters in vivo. Taken together, these findings provide a novel insight into an additional layer of modulation of bacterial RNAP activity.

Streptomyces Cytochrome P450 Enzymes and Their Roles in the Biosynthesis of Macrolide Therapeutic Agents

The study of the genus Streptomyces is of particular interest because it produces a wide array of clinically important bioactive molecules. The genomic sequencing of many Streptomyces species has revealed unusually large numbers of cytochrome P450 genes, which are involved in the biosynthesis of secondary metabolites. Many macrolide biosynthetic pathways are catalyzed by a series of enzymes in gene clusters including polyketide and non-ribosomal peptide synthesis. In general, Streptomyces P450 enzymes accelerate the final, post-polyketide synthesis steps to enhance the structural architecture of macrolide chemistry. In this review, we discuss the major Streptomyces P450 enzymes research focused on the biosynthetic processing of macrolide therapeutic agents, with an emphasis on their biochemical mechanisms and structural insights.

Streptomyces monashensis sp. nov., a novel mangrove soil actinobacterium from East Malaysia with antioxidative potential

A new Streptomyces species discovered from Sarawak mangrove soil is described, with the proposed name - Streptomyces monashensis sp. nov. (strain MUSC 1JT). Taxonomy status of MUSC 1JT was determined via polyphasic approach. Phylogenetic and chemotaxonomic properties of strain MUSC 1JT were in accordance with those known for genus Streptomyces. Based on phylogenetic analyses, the strains closely related to MUSC 1JT were Streptomyces corchorusii DSM 40340T (98.7%), Streptomyces olivaceoviridis NBRC 13066T (98.7%), Streptomyces canarius NBRC 13431T (98.6%) and Streptomyces coacervatus AS-0823T (98.4%). Outcomes of DNA-DNA relatedness between strain MUSC 1JT and its closely related type strains covered from 19.7 ± 2.8% to 49.1 ± 4.3%. Strain MUSC 1JT has genome size of 10,254,857 bp with DNA G + C content of 71 mol%. MUSC 1JT extract exhibited strong antioxidative activity up to 83.80 ± 4.80% in the SOD assay, with significant cytotoxic effect against colon cancer cell lines HCT-116 and SW480. Streptomyces monashensis MUSC 1JT (=DSM 103626T = MCCC 1K03221T) could potentially be a producer of novel bioactive metabolites; hence discovery of this new species may be highly significant to the biopharmaceutical industry as it could lead to development of new and useful chemo-preventive drugs.

Growth and differentiation properties of pikromycin-producing Streptomyces venezuelae ATCC15439

Streptomycetes naturally produce a variety of secondary metabolites, in the process of physiological differentiation. Streptomyces venezuelae differentiates into spores in liquid media, serving as a good model system for differentiation and a host for exogenous gene expression. Here, we report the growth and differentiation properties of S. venezuelae ATCC-15439 in liquid medium, which produces pikromycin, along with genome-wide gene expression profile. Comparison of growth properties on two media (SPA, MYM) revealed that the stationary phase cell viability rapidly decreased in SPA. Submerged spores showed partial resistance to lysozyme and heat, similar to what has been observed for better-characterized S. venezuelae ATCC10712, a chloramphenicol producer. TEM revealed that the differentiated cells in the submerged culture showed larger cell size, thinner cell wall than the aerial spores. We analyzed transcriptome profiles of cells grown in liquid MYM at various growth phases. During transition and/or stationary phases, many differentiationrelated genes were well expressed as judged by RNA level, except some genes forming hydrophobic coats in aerial mycelium. Since submerged spores showed thin cell wall and partial resistance to stresses, we examined cellular expression of MreB protein, an actin-like protein known to be required for spore wall synthesis in Streptomycetes. In contrast to aerial spores where MreB was localized in septa and spore cell wall, submerged spores showed no detectable signal. Therefore, even though the mreB transcripts are abundant in liquid medium, its protein level and/or its interaction with spore wall synthetic complex appear impaired, causing thinner- walled and less sturdy spores in liquid culture.

Complete reconstitution of the diverse pathways of gentamicin B biosynthesis

Gentamicin B (GB), a valuable starting material for the preparation of the semisynthetic aminoglycoside antibiotic isepamicin, is produced in trace amounts by the wild-type Micromonospora echinospora. While the biosynthetic pathway to GB has remained obscure for decades, we have now identified three hidden pathways to GB production via seven hitherto unknown intermediates in M. echinospora. The narrow substrate specificity of a key glycosyltransferase and the C6′-amination enzymes, in combination with the weak and unsynchronized gene expression of the 2′-deamination enzymes, limit GB production in M. echinospora. The crystal structure of the aminotransferase involved in C6′-amination explains its substrate specificity. Some of the new intermediates displayed similar premature termination codon readthrough activity but with reduced toxicity compared to the natural aminoglycoside G418. This work not only led to the discovery of unknown biosynthetic routes to GB, but also demonstrated the potential to mine new aminoglycosides from nature for drug discovery.

Streptomycetes: Surrogate hosts for the genetic manipulation of biosynthetic gene clusters and production of natural products

Due to the worldwide prevalence of multidrug-resistant pathogens and high incidence of diseases such as cancer, there is an urgent need for the discovery and development of new drugs. Nearly half of the FDA-approved drugs are derived from natural products that are produced by living organisms, mainly bacteria, fungi, and plants. Commercial development is often limited by the low yield of the desired compounds expressed by the native producers. In addition, recent advances in whole genome sequencing and bioinformatics have revealed an abundance of cryptic biosynthetic gene clusters within microbial genomes. Genetic manipulation of clusters in the native host is commonly used to awaken poorly expressed or silent gene clusters, however, the lack of feasible genetic manipulation systems in many strains often hinders our ability to engineer the native producers. The transfer of gene clusters into heterologous hosts for expression of partial or entire biosynthetic pathways is an approach that can be used to overcome this limitation. Heterologous expression also facilitates the chimeric fusion of different biosynthetic pathways, leading to the generation of "unnatural" natural products. The genus Streptomyces is especially known to be a prolific source of drugs/antibiotics, its members are often used as heterologous expression hosts. In this review, we summarize recent applications of Streptomyces species, S. coelicolor, S. lividans, S. albus, S. venezuelae and S. avermitilis, as heterologous expression systems.

Genome mining reveals the biosynthetic potential of the marine-derived strain Streptomyces marokkonensis M10

Marine streptomycetes are rich sources of natural products with novel structures and interesting biological activities, and genome mining of marine streptomycetes facilitates rapid discovery of their useful products. In this study, a marine-derived Streptomyces sp. M10 was revealed to share a 99.02% 16S rDNA sequence identity with that of Streptomyces marokkonensis Ap1^T, and was thus named S. marokkonensis M10. To further evaluate its biosynthetic potential, the 7,207,169 bps of S. marokkonensis M10 genome was sequenced. Genomic sequence analysis for potential secondary metabolite-associated gene clusters led to the identification of at least three polyketide synthases (PKSs), six non-ribosomal peptide synthases (NRPSs), one hybrid NRPS-PKS, two lantibiotic and five terpene biosynthetic gene clusters. One type I PKS gene cluster was revealed to share high nucleotide similarity with the candicidin/FR008 gene cluster, indicating the capacity of this microorganism to produce polyene macrolides. This assumption was further verified by isolation of two polyene family compounds PF1 and PF2, which have the characteristic UV adsorption at 269, 278, 290 nm (PF1) and 363, 386 and 408 nm (PF2), respectively. S. marokkonensis M10 is therefore a new source of polyene metabolites. Further studies on S. marokkonensis M10 will provide more insights into natural product biosynthesis potential of related streptomycetes. This is also the first report to describe the genome sequence of S. marokkonensis-related strain.