Streptomyces sp. VN1, a producer of diverse metabolites including non-natural furan-type anticancer compound.

Streptomyces sp. VN1 was isolated from the coastal region of Phu Yen Province (central Viet Nam). Morphological, physiological, and whole genome phylogenetic analyses suggested that strain Streptomyces sp. VN1 belonged to genus Streptomyces. Whole genome sequencing analysis showed its genome was 8,341,703 base pairs in length with GC content of 72.5%. Diverse metabolites, including cinnamamide, spirotetronate antibiotic lobophorin A, diketopiperazines cyclo-L-proline-L-tyrosine, and a unique furan-type compound were isolated from Streptomyces sp. VN1. Structures of these compounds were studied by HR-Q-TOF ESI/MS/MS and 2D NMR analyses. Bioassay-guided purification yielded a furan-type compound which exhibited in vitro anticancer activity against AGS, HCT116, A375M, U87MG, and A549 cell lines with IC50 values of 40.5, 123.7, 84.67, 50, and 58.64 µM, respectively. In silico genome analysis of the isolated Streptomyces sp. VN1 contained 34 gene clusters responsible for the biosynthesis of known and/or novel secondary metabolites, including different types of terpene, T1PKS, T2PKS, T3PKS, NRPS, and hybrid PKS-NRPS. Genome mining with HR-Q-TOF ESI/MS/MS analysis of the crude extract confirmed the biosynthesis of lobophorin analogs. This study indicates that Streptomyces sp. VN1 is a promising strain for biosynthesis of novel natural products.

Exploration of cryptic organic photosensitive compound as Zincphyrin IV in Streptomyces venezuelae ATCC 15439.

Zincphyrin IV is a potential organic photosensitizer which is of significant interest for applications in biomedicine, materials science, agriculture (as insecticide), and chemistry. Most studies on Zincphyrin are focused on Zincphyrin III while biosynthesis and application of Zincphyrin IV is comparatively less explored. In this study, we explored Zincphyrin IV production in Streptomyces venezuelae ATCC 15439 through combination of morphology engineering and "One strain many compounds" approach. The morphology engineering followed by change in culture medium led to activation of cryptic Zincphyrin IV biosynthetic pathway in S. venezuelae with subsequent detection of Zincphyrin IV. Morphology engineering applied in S. venezuelae increased the biomass from 7.17 to 10.5 mg/mL after 48 h of culture. Moreover, morphology of engineered strain examined by SEM showed reduced branching and fragmentation of mycelia. The distinct change in color of culture broth visually demonstrated the activation of the cryptic biosynthetic pathway in S. venezuelae. The production of Zincphyrin IV was found to be initiated after overexpression ssgA, resulting in the increase in titer from 4.21 to 7.54 µg/mL. Furthermore, Zincphyrin IV demonstrated photodynamic antibacterial activity against Bacillus subtilis and photodynamic anticancer activity against human ovarian carcinoma cell lines.

High-Throughput Detection of Bacterial Community and Its Drug-Resistance Profiling From Local Reclaimed Wastewater Plants.

Treated wastewater from reclaimed facilities (WWTP) has become a reusable source for a variety of applications, such as agricultural irrigation. However, it is also a potential reservoir of clinically-relevant multidrug resistant (MDR) pathogens, including ESKAPE (Enterococcus faecium and Streptococcus surrogates, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter species along with the emerging nosocomial Escherichia strains). This study was performed to decipher the bacterial community structure through Illumina high throughput 16S rRNA gene sequencing, and to determine the resistance profile using the Sensititre antimicrobial susceptibility test (AST) conforming to clinical lab standards (NCCLS). Out of 1747 bacterial strains detected from wastewater influent and effluent, Pseudomonas was the most predominant genus related to ESKAPE in influent, with sequence reads corresponding to 21.356%, followed by Streptococcus (6.445%), Acinetobacter (0.968%), Enterococcus (0.063%), Klebsiella (0.038%), Escherichia (0.028%) and Staphylococcus (0.004%). Despite the different treatment methods used, the effluent still revealed the presence of some Pseudomonas strains (0.066%), and a wide range of gram-positive cocci, including Staphylococcus (0.194%), Streptococcus (0.63%) and Enterococcus (0.037%), in addition to gram-negative Acinetobacter (0.736%), Klebsiella (0.1%), and Escherichia sub-species (0.811%). The AST results indicated that the strains Escherichia along with Klebsiella and Acinetobacter, isolated from the effluent, displayed resistance to 11 antibiotics, while Pseudomonas was resistant to 7 antibiotics, and Streptococcus along with Staphylococcus were resistant to 9 antibiotics. Results herein, proved the existence of some nosocomial MDR pathogens, known for ESKAPE, with potential drug resistance transfer to the non-pathogen microbes, requiring targeted remediation.

Modular pathway engineering for resveratrol and piceatannol production in engineered Escherichia coli.

Resveratrol and its ortho-hydroxylated derivative piceatannol were biosynthesized by modular pathway engineering in Escherichia coli. The biosynthetic pathway was divided into three different modules. Module I includes polyketide biosynthetic genes; module II genes include acetyl-CoA and malonyl-CoA pool-enhancing genes from three different organisms; and module III genes are regiospecific 3'-hydroxylating enzymes. E. coli BL21(DE3) with module I produced 8.6 mg/L of resveratrol from exogenously fed 1 mM p-coumaric acid after 72 h. Combination of module I and acetyl-CoA supplementing module IIb genes from N. farcinica IFM10152 produced 2.5-fold higher (60 mg/L) titer of resveratrol than the module IIa genes from E. coli. The exogenous supplementation of sodium acetate further enhanced production to 64 mg/L. Furthermore, module I with module IIc harboring matBC from S. coelicolor A3(2) produced 73 mg/L of resveratrol, which was elevated to 151 mg/L upon supplementing disodium malonate exogenously. This increment is 17.5-fold higher than module I harboring E. coli BL21(DE3). The combination of module I and two different module II genes yielded 137 mg/L resveratrol when supplemented with both sodium acetate and disodium malonate. The high resveratrol-producing combination module was further modified with incorporation of hpaBC for the ortho-hydroxylation of resveratrol to produce piceatannol. The engineered strain harboring modules I, IIc and III produced 124 mg/L of piceatannol, the highest titer after 72 h in disodium malonate-supplemented strain, which is 2-fold higher than in non-supplemented strain. The remaining resveratrol was about 30 mg/L. Furthermore, caffeic acid (85.5 mg/L) was also produced in the same strain. Resveratrol and piceatannol were biosynthesized along with caffeic acid by three different modules overexpressing acetate and malonate assimilation pathway genes from three different sources. The production titer of both resveratrol and piceatannol could be achieved higher upon blocking acetyl-CoA and malonyl-CoA utilizing pathway genes in host strain.

Implication of orphan histidine kinase (OhkAsp) in biosynthesis of doxorubicin and daunorubicin in Streptomyces peucetius ATCC 27952.

The orphan histidine kinase (HK) from Streptomyces peucetius ATCC 27952 (ohkAsp) was found to be implicated in the regulation of doxorubicin (DOX)/daunorubicin (DNR) biosynthesis, self-defense and developmental attributes. OhkAsp is a homolog of OhkA from Streptomyces coelicolor and Streptomyces avermitilis (with 73 and 75% identity). As in its homologs, S. peucetius mutant with deletion of ohkAsp was found to enhance metabolite biosynthesis and impaired the morphological differentiation. But, unlike its homologs from Streptomyces coelicolor and Streptomyces avermitilis, differential enhancement in level of secondary metabolite production was found in overexpression mutants apart from deletion mutant. The deflection in characteristics of OhkA in its homologue from S. peucetius ATCC 27952, and its imminent implications was monitered by making various mutants with differential expression level of ohkAsp. The variations were observed in the morphology of mutants, transcriptional level of effectors and regulators of DOX/DNR biosynthesis pathway, DOX/DNR precursor pool and biomass accumulation. Based on comparisons of domain arrangements among its homologs, Low Complexity Region (LCR) present on the OhkAsp was the only domain that stood out. Further, the LCR on OhkAsp was found to be overlapping with a putative receiver domain responsible for interaction with response regulator. The imminent implications of differential expression level of ohkAsp on: regulation and biosynthesis of DOX/DNR, morphological differentiation, DOX/DNR precursor pool and biomass accumulation were explored in this study.

Genome-guided exploration of metabolic features of Streptomyces peucetius ATCC 27952: past, current, and prospect.

Streptomyces peucetius ATCC 27952 produces two major anthracyclines, doxorubicin (DXR) and daunorubicin (DNR), which are potent chemotherapeutic agents for the treatment of several cancers. In order to gain detailed insight on genetics and biochemistry of the strain, the complete genome was determined and analyzed. The result showed that its complete sequence contains 7187 protein coding genes in a total of 8,023,114 bp, whereas 87% of the genome contributed to the protein coding region. The genomic sequence included 18 rRNA, 66 tRNAs, and 3 non-coding RNAs. In silico studies predicted ~ 68 biosynthetic gene clusters (BCGs) encoding diverse classes of secondary metabolites, including non-ribosomal polyketide synthase (NRPS), polyketide synthase (PKS I, II, and III), terpenes, and others. Detailed analysis of the genome sequence revealed versatile biocatalytic enzymes such as cytochrome P450 (CYP), electron transfer systems (ETS) genes, methyltransferase (MT), glycosyltransferase (GT). In addition, numerous functional genes (transporter gene, SOD, etc.) and regulatory genes (afsR-sp, metK-sp, etc.) involved in the regulation of secondary metabolites were found. This minireview summarizes the genome-based genome mining (GM) of diverse BCGs and genome exploration (GE) of versatile biocatalytic enzymes, and other enzymes involved in maintenance and regulation of metabolism of S. peucetius. The detailed analysis of genome sequence provides critically important knowledge useful in the bioengineering of the strain or harboring catalytically efficient enzymes for biotechnological applications.

Biosynthesis of novel 7,8-dihydroxyflavone glycoside derivatives and in silico study of their effects on BACE1 inhibition.

7,8-Dihydroxyflavone (7,8-DHF) has been conjugated with glucose moiety to produce glucoside derivatives. Three analogues of 7,8-DHF (7-O-ß-d-glucosyl-8-hydroxyflavone, 7-hydroxy-8-O-ß-d-glucosyl flavone, and 7,8-di-O-ß-d-glucosylflavone) have been successfully produced from in vitro reaction using glycosyltransferase of Bacillus licheniformis. Production of these 7,8-DHF derivatives were shifted to cheaper and easier approach in this study by using engineered Escherichia coli BL21 (DE3) ΔpgiΔzwfΔushA cells in which the flow of glucose-6-phospahte toward glycolysis and pentose phosphate pathway and hydrolysis of UDP-α-d-glucose were blocked while directing the carbon flux toward UDP-α-d-glucose by overexpressing UDP-α-d-glucose pathway genes. Supplementation of 300 µM of 7,8-DHF to the culture resulted in production of 171 µM of 7-O-ß-d-glucosyl-8-hydroxyflavone, 68 µM of 7-hydroxy-8-O-ß-d-glucoxyflavone, and 55 µM of 7,8-di-O-ß-d-glucoxyflavone in laboratory-scale 3-L fermentor, representing 98% bioconversion of initially fed substrate to respective glucoside derivatives within 48 H. These products were characterized by high-performance liquid chromatography-photodiode array (HPLC-PDA), HPLC-PDA-quadruple time of flight-electron spray ionization mass spectrometry, and nuclear magnetic resonance analyses. These newly synthesized derivatives were found to be able to interact with amino acids of active site of human ß-site amyloid precursor protein cleaving ß-site amyloid precursor protein cleaving enzyme 1 (BACE1) ß-secretase enzyme in in silico studies, thus displaying possible application in cure of Alzheimer's disease.

Marine Rare Actinobacteria: Isolation, Characterization, and Strategies for Harnessing Bioactive Compounds.

Actinobacteria are prolific producers of thousands of biologically active natural compounds with diverse activities. More than half of these bioactive compounds have been isolated from members belonging to actinobacteria. Recently, rare actinobacteria existing at different environmental settings such as high altitudes, volcanic areas, and marine environment have attracted attention. It has been speculated that physiological or biochemical pressures under such harsh environmental conditions can lead to the production of diversified natural compounds. Hence, marine environment has been focused for the discovery of novel natural products with biological potency. Many novel and promising bioactive compounds with versatile medicinal, industrial, or agricultural uses have been isolated and characterized. The natural compounds cannot be directly used as drug or other purposes, so they are structurally modified and diversified to ameliorate their biological or chemical properties. Versatile synthetic biological tools, metabolic engineering techniques, and chemical synthesis platform can be used to assist such structural modification. This review summarizes the latest studies on marine rare actinobacteria and their natural products with focus on recent approaches for structural and functional diversification of such microbial chemicals for attaining better applications.

Saccharopolyspora Species: Laboratory Maintenance and Enhanced Production of Secondary Metabolites.

Saccharopolyspora spp. are aerobic, Gram-positive, non-acid-fast, and non-motile actinomycetes. Various species of the genus Saccharopolyspora have been reported with an ability to produce various bioactive compounds for pharmaceutical and agricultural uses. This unit includes general protocols for the laboratory maintenance of Saccharopolyspora species, including growth in liquid medium, growth on solid agar, long-term storage, and generation of a higher producer strain by mutagenesis. Saccharopolyspora spinosa ATCC 49460 is used as a prototype for explaining the considerations for efficient laboratory maintenance of Saccharopolyspora spp. Saccharopolyspora spinosa is a producer of spinosad, a prominent insecticide with selective activity against various insects. © 2017 by John Wiley & Sons, Inc.

Microbial production of astilbin, a bioactive rhamnosylated flavanonol, from taxifolin.

Flavonoids are plant-based polyphenolic biomolecules with a wide range of biological activities. Glycosylated flavonoids have drawn special attention in the industries as it improves solubility, stability, and bioactivity. Herein, we report the production of astilbin (ATN) from taxifolin (TFN) in genetically-engineered Escherichia coli BL21(DE3). The exogenously supplied TFN was converted to ATN by 3-O-rhamnosylation utilizing the endogeneous TDP-L-rhamnose in presence of UDP-glycosyltransferase (ArGT3, Gene Bank accession number: At1g30530) from Arabidopsis thaliana. Upon improving the intracellular TDP-L-rhamnose pool by knocking out the chromosomal glucose phosphate isomerase (pgi) and D-glucose-6-phosphate dehydrogenase (zwf) deletion along with the overexpression of rhamnose biosynthetic pathway increases the biotransformation product, ATN with total conversion of ~49.5 ± 1.67% from 100 µM of taxifolin. In addition, the cytotoxic effect of taxifolin-3-O-rhamnoside on PANC-1 and A-549 cancer cell lines was assessed for establishing ATN as potent antitumor compound.

Overexpression of a pathway specific negative regulator enhances production of daunorubicin in bldA deficient Streptomyces peucetius ATCC 27952.

The dnrO gene is the first regulator to be activated in the daunorubicin (DNR) biosynthesis pathway of Streptomyces peucetius ATCC 27952. DnrO is known for its self-repression capability while it activates rest of the DNR biosynthesis pathway through cascades of regulatory events. S. peucetius was found to contain no functional copy of bldA-tRNA while a detailed examination of dnrO codons reveals the presence of TTA codon, which is rarely encoded by bldA-tRNA. Therefore, for evaluating the role of dnrO in DNR production, multiple engineered strains of S. peucetius were generated by heterologously expressing bldA, dnrO and combination of bldA and dnrO. Using these strains, the effects of heterologously expressed bldA and overexpressed dnrO were evaluated on pathway specific regulators, mycelial densities and production of DNR. The results showed that the transcription level of dnrO and master regulator dnrI, was found to be elevated in bldA containing strain in comparison to dnrO overexpressed strain. The bldA containing strain produces 45.7% higher DNR than bldA deficient wild type strain from culture broth with OD600 of 1.45 at 72h. Heterologous expression of bldA-tRNA is accounted for increased transcription levels of the DNR pathway specific regulators and enhanced DNR production.

Enhanced production of nargenicin A1 and creation of a novel derivative using a synthetic biology platform.

Nargenicin A1, an antibacterial produced by Nocardia sp. CS682 (KCTC 11297BP), demonstrates effective activity against various Gram-positive bacteria. Hence, we attempted to enhance nargenicin A1 production by utilizing the cumulative effect of synthetic biology, metabolic engineering and statistical media optimization strategies. To facilitate the modular assembly of multiple genes for genetic engineering in Nocardia sp. CS682, we constructed a set of multi-monocistronic vectors, pNV18L1 and pNV18L2 containing hybrid promoter (derived from ermE* and promoter region of neo r ), ribosome binding sites (RBS), and restriction sites for cloning, so that each cloned gene was under its own promoter and RBS. The multi-monocistronic vector, pNV18L2 containing transcriptional terminator showed better efficiency in reporter gene assay. Thus, multiple genes involved in the biogenesis of pyrrole moiety (ngnN2, ngnN3, ngnN4, and ngnN5 from Nocardia sp. CS682), glucose utilization (glf and glk from Zymomonas mobilis), and malonyl-CoA synthesis (accA2 and accBE from Streptomyces coelicolor A3 (2)), were cloned in pNV18L2. Further statistical optimization of specific precursors (proline and glucose) and their feeding time led to ~84.9 mg/L nargenicin from Nocardia sp. GAP, which is ~24-fold higher than Nocardia sp. CS682 (without feeding). Furthermore, pikC from Streptomyces venezuelae was expressed to generate Nocardia sp. PikC. Nargenicin A1 acid was characterized as novel derivative of nargenicin A1 produced from Nocardia sp. PikC by mass spectrometry (MS) and nuclear magnetic resonance (NMR) analyses. We also performed comparative analysis of the anticancer and antibacterial activities of nargenicin A1 and nargenicin A1 acid, which showed a reduction in antibacterial potential for nargenicin A1 acid. Thus, the development of an efficient synthetic biological platform provided new avenues for enhancing or structurally diversifying nargenicin A1 by means of pathway designing and engineering.

Herboxidiene biosynthesis, production, and structural modifications: prospect for hybrids with related polyketide.

Herboxidiene is a polyketide with a diverse range of activities, including herbicidal, anti-cholesterol, and pre-mRNA splicing inhibitory effects. Thus, production of the compound on the industrial scale is in high demand, and various rational metabolic engineering approaches have been employed to enhance the yield. Directing the precursors and cofactors pool toward the production of polyketide compounds provides a rationale for developing a good host for polyketide production. Due to multiple promising biological activities, the production of a number of herboxidiene derivatives has been attempted in recent years in a search for the key to improve its potency and to introduce new activities. Structural diversification through combinatorial biosynthesis was attempted, utilizing the heterologous expression of substrate-flexible glucosyltransferase (GT) and cytochrome P450 in Streptomyces chromofuscus to generate structurally and functionally diverse derivatives of herboxidiene. The successful attempt confirmed that the strain was amenable to heterologous expression of foreign polyketide synthase (PKS) or post-PKS modification genes, providing the foundation for generating novel or hybrid polyketides.

Structural modification of herboxidiene by substrate-flexible cytochrome P450 and glycosyltransferase.

Herboxidiene is a natural product produced by Streptomyces chromofuscus exhibiting herbicidal activity as well as antitumor properties. Using different substrate-flexible cytochrome P450s and glycosyltransferase, different novel derivatives of herboxidiene were generated with structural modifications by hydroxylation or epoxidation or conjugation with a glucose moiety. Moreover, two isomers of herboxidiene containing extra tetrahydrofuran or tetrahydropyran moiety in addition to the existing tetrahydropyran moiety were characterized. The hydroxylated products for both of these compounds were also isolated and characterized from S. chromofuscus PikC harboring pikC from the pikromycin gene cluster of Streptomyces venezuelae and S. chromofuscus EryF harboring eryF from the erythromycin gene cluster of Saccharopolyspora erythraea. The compounds generated were characterized by high-resolution quadrupole-time-of-flight electrospray ionization mass spectrometry (HR-QTOF-ESI/MS) and (1)H- and (13)C-nuclear magnetic resonance (NMR) analyses. The evaluation of antibacterial activity against three Gram-positive bacteria, Micrococcus luteus, Bacillus subtilis, and Staphylococcus aureus, indicated that modification resulted in a transition from anticancer to antibacterial potency.

Enhanced production of nargenicin A(1) and generation of novel glycosylated derivatives.

Nargenicin A1, an antibacterial polyketide macrolide produced by Nocardia sp. CS682, was enhanced by increasing the pool of precursors using different sources. Furthermore, by using engineered strain Nocardia sp. ACC18 and supplementation of glucose and glycerol, enhancement was ~7.1 fold in comparison to Nocardia sp. CS682 without supplementation of any precursors. The overproduced compound was validated by mass spectrometry and nuclear magnetic resonance analyses. The novel glycosylated derivatives of purified nargenicin A1 were generated by efficient one-pot reaction systems in which the syntheses of uridine diphosphate (UDP)-α-D-glucose and UDP-α-D-2-deoxyglucose were modified and combined with glycosyltransferase (GT) from Bacillus licheniformis. Nargenicin A1 11-O-ß- D-glucopyranoside, nargenicin A1 18-O-ß-D-glucopyranoside, nargenicin A111 18-O-ß-D- diglucopyranoside, and nargenicin 11-O-ß-D-2-deoxyglucopyranoside were generated. Nargenicin A1 11-O-ß-D-glucopyranoside was structurally elucidated by ultra-high performance liquid chromatography-photodiode array (UPLC-PDA) conjugated with high-resolution quantitative time-of-flight-electrospray ionization mass spectroscopy (HR-QTOF ESI-MS/MS), supported by one- and two-dimensional nuclear magnetic resonance studies, whereas other nargenicin A1 glycosides were characterized by UPLC-PDA and HR-QTOF ESI-MS/MS analyses. The overall conversion studies indicated that the one-pot synthesis system is a highly efficient strategy for production of glycosylated derivatives of compounds like macrolides as well. Furthermore, assessment of solubility indicated that there was enhanced solubility in the case of glycoside, although a substantial increase in activity was not observed.

Metabolic engineering of rational screened Saccharopolyspora spinosa for the enhancement of spinosyns A and D production.

Spinosyns A and D are potent ingredient for insect control with exceptional safety to non-target organisms. It consists of a 21-carbon tetracyclic lactone with forosamine and tri-O-methylated rhamnose which are derived from S-adenosylmethionine. Although previous studies have revealed the involvement of metK1 (S-adenosylmethionine synthetase), rmbA (glucose-1-phosphate thymidylyltransferase), and rmbB (TDP-D-glucose-4, 6-dehydratase) in the biosynthesis of spinosad, expression of these genes into rational screened Saccharopolyspora spinosa (S. spinosa MUV) has not been elucidated till date. In the present study, S. spinosa MUV was developed to utilize for metabolic engineering. The yield of spinosyns A and D in S. spinosa MUV was 244 mg L(-1) and 129 mg L(-1), which was 4.88-fold and 4.77-fold higher than that in the wild-type (50 mg L(-1) and 27 mg L(-1)), respectively. To achieve the better production; positive regulator metK1-sp, rmbA and rmbB genes from Streptomyces peucetius, were expressed and co-expressed in S. spinosa MUV under the control of strong ermE* promoter, using an integration vector pSET152 and expression vector pIBR25, respectively. Herewith, the genetically engineered strain of S. spinosa MUV, produce spinosyns A and D up to 372/217 mg L(-1) that is 7.44/8.03-fold greater than that of wild type. This result demonstrates the use of metabolic engineering on rationally developed high producing natural variants for the production.

Enzymatic glycosylation of the topical antibiotic mupirocin.

Mupirocin is a commercially available antibiotic that acts on bacterial isoleucyl-tRNA synthetase, thereby inhibiting protein synthesis and preventing bacterial infection. An in vitro glycosylation approach was applied to synthesize glycoside derivatives of mupirocin using different NDP-sugars and glycosyltransferase from Bacillus licheniformis. Ultra pressure liquid chromatography-photo diode array analyses of the reaction mixtures revealed the generation of product peak(s). The results were further supported by high-resolution quadruple time of flight electrospray ionization mass spectrometry analyses. The product purified from the reaction mixture with UDP-D-glucose was subjected to NMR analysis, and the structure was determined to be mupirocin 6-O-ß-D-glucoside. Other glycoside analogs of mupirocin were determined based on high-resolution mass analyses. Antibacterial activity assays against Staphylococcus aureus demonstrated complete loss of antibacterial activity after glucosylation of mupirocin at the 6-hydroxyl position.