Biosynthesized selenium nanoparticles (SeNPs) have attracted much attention because of their unique physical, chemical, and biological properties. The microbial reduction of selenium salts to SeNPs has great potential, while there is a lack of elite strains. In this study, we explored the reduction of Na₂SeO₃ by Streptomyces avermitilis into SeNPs. The colonies and hyphae of the strain and the synthesized SeNPs were characterized by optical microscopy, scanning electron microscopy (SEM), transmission electron microscope (TEM), energy dispersive spectrometry (EDS), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR). At the same time, the inhibitory activity of SeNPs on Fusarium oxysporum, the main pathogen causing root rot of Lycium barbarum, was studied. The results showed that S. avermitilis converted Na₂SeO₃ into SeNPs and tolerated 300 mmol/L Na₂SeO₃, demonstrating strong tolerance. S. avermitilis synthesized spherical SeNPs in the cytoplasm, and most of SeNPs had a diameter of about 100 nm and were released by hyphal fracture. The SeNPs synthesized by S. avermitilis were amorphous, and their surfaces were dominated by C and Se, with the existence of O, N and other elements. SeNPs had functional groups such as -OH, C=O, C-N, and C-H, which were closely related to the stability and biological activity of SeNPs. The SeNPs synthesized by S. avermitilis showcased significant inhibitory activity on F. oxysporum, and 25.0 μmol/mL SeNPs showcased the inhibition rate of 77.61% and EC₅₀ of 0.556 μmol/mL. In conclusion, S. avermitilis can tolerate high Na₂SeO₃ stress and mediate the synthesis of SeNPs. The synthesized SeNPs have good stability and strong inhibitory activity, demonstrating the potential application value in the preparation of SeNPs and the control of L. barbarum root rot.
Streptomyces/metabolism* ; Fusarium/drug effects* ; Lycium/microbiology* ; Selenium/metabolism* ; Nanoparticles/chemistry* ; Plant Diseases/microbiology* ; Metal Nanoparticles/chemistry* ; Antifungal Agents/pharmacology*

In recent years, potato scab caused by Streptomyces scabies is aggravating year by year, becoming an industrial problem urgently to be resolved. Screening antagonistic bacteria with good inhibitory effect and wide adaptability is the main measure to realize effective prevention and control of the disease. This study screened three strains of antagonistic bacteria DXT2-4, T2-1 and 21-14 with good inhibitory effect on S. scabies by using plate standoff test, and identified them as Bacillus altitudinis, Bacillus safensis and Bacillus pumilus, respectively, based on morphological characteristics, physiological and biochemical properties, and 16S rRNA gene sequences. DXT2-4, T2-1 and 21-14 showed the pot control efficacy of 68.83%, 48.57%, and 57.14%, respectively. The field control efficacy of the three strains was 59.48%, 34.58% and 51.75% in Hulun Buir, Inner Mongolia Autonomous Region and 55.14%, 36.05%, and 49.05% in Huizhou, Guangdong. The three strains could grow normally in the media with pH 1.0-13.0 and with 1%-11% NaCl, and they had inhibitory effects on Rhizoctonia solani, Verticillium dahliae, Alternaria solani, and Fusarium oxysporum. The indole-3-acetic acid yields of DXT2-4, T2-1, and 21-14 were 2.23, 1.11, and 1.67 mg/L, respectively. DXT2-4 and 21-14 demonstrated strong abilities to solubilize phosphorus. The optimal carbon source, nitrogen source, and inorganic salt for fermentation of strain DXT2-4 were 2% molasses+2% corn starch, 2% soybean meal, and 0.3% MgSO₄·7H₂O, respectively. These findings suggest the three strains of bacteria can efficiently inhibit the growth of S. scabies and have strong environmental adaptability. Particularly, DXT2-4 has the best effects of inhibiting the disease and promoting plant growth, showing a high development value and broad application prospects, this is of great significance for promoting sustainable potato production and ensuring the environmentally sound utilization of resources.
Streptomyces/metabolism* ; Fermentation ; Plant Diseases/prevention & control* ; Solanum tuberosum/growth & development* ; Bacillus/growth & development* ; Antibiosis

Lysobacter harbors a plethora of cryptic biosynthetic gene clusters (BGCs), albeit only a limited number have been analyzed to date. In this study, we described the activation of a cryptic polyketide synthase (PKS)/nonribosomal peptide synthetase (NRPS) gene cluster (lsh) in Lysobacter sp. DSM 3655 through promoter engineering and heterologous expression in Streptomyces sp. S001. As a result of this methodology, we were able to isolate two novel linear lipopeptides, lysohexaenetides A (1) and B (2), from the recombinant strain S001-lsh. Furthermore, we proposed the biosynthetic pathway for lysohexaenetides and identified LshA as another example of entirely iterative bacterial PKSs. This study highlights the potential of heterologous expression systems in uncovering cryptic biosynthetic pathways in Lysobacter genomes, particularly in the absence of genetic manipulation tools.
Lysobacter/metabolism* ; Streptomyces/metabolism* ; Lipopeptides/metabolism* ; Polyketide Synthases/genetics* ; Multigene Family

Natural cyclohexapeptide AFN A₁ fromStreptomyces alboflavus 313 has moderate antibacterial and antitumor activities. An artificial designed AFN A₁ homodimer, di-AFN A₁, is an antibiotic exhibiting 10 to 150 fold higher biological activities, compared with the monomer. Unfortunately, the yield of di-AFN A₁ is very low (0.09 ± 0.03 mg·L^-1) in the engineered strain Streptomyces alboflavus 313_hmtS (S. albo/313_hmtS), which is not friendly to be genetically engineered for titer improvement of di-AFN A₁ production. In this study, we constructed a biosynthetic gene cluster for di-AFN A₁ and increased its production through heterologous expression. During the collection of di-AFN A₁ biosynthetic genes, the afn genes were located at three sites of S. alboflavus 313 genome. The di-AFN A₁ biosynthetic gene cluster (BGC) was first assembled on one plasmid and introduced into the model strain Streptomyces lividans TK24, which produced di-AFN A₁ at a titer of 0.43 ± 0.01 mg·L^-1. To further increase the yield of di-AFN A₁, the di-AFN A₁ BGC was multiplied and split to mimic the natural afn biosynthetic genes, and the production of di-AFN A₁ increased to 0.62 ± 0.11 mg·L^-1 in S. lividans TK24 by the later strategy. Finally, different Streptomyces hosts were tested and the titer of di-AFN A₁ increased to 0.81 ± 0.17 mg·L^-1, about 8.0-fold higher than that in S. albo/313_hmtS. Successful heterologous expression of di-AFN A₁ with a remarkable increased titer will greatly facilitate the following synthetic biological study and drug development of this dimeric cyclohexapeptide.
Cloning, Molecular ; Streptomyces/metabolism* ; Multigene Family ; Anti-Bacterial Agents/metabolism* ; Plasmids/genetics*

Natamycin is a safe and efficient antimycotics which is widely used in food and medicine industry. The polyene macrolide compound, produced by several bacterial species of the genus Streptomyces, is synthesized by type Ⅰ polyketide synthases using acetyl-CoA, malonyl-CoA, and methylmalonyl-CoA as substrates. In this study, four pathways potentially responsible for the supply of the three precursors were evaluated to identify the effective precursor supply pathway which can support the overproduction of natamycin in Streptomyces gilvosporeus, a natamycin-producing wild-type strain. The results showed that over-expressing acetyl-CoA synthetase and methylmalonyl-CoA mutase increased the yield of natamycin by 44.19% and 20.51%, respectively, compared with the wild type strain under shake flask fermentation. Moreover, the yield of natamycin was increased by 66.29% compared with the wild-type strain by co-overexpression of acetyl-CoA synthetase and methylmalonyl-CoA mutase. The above findings will facilitate natamycin strain improvement as well as development of strains for producing other polyketide compounds.
Natamycin/metabolism* ; Methylmalonyl-CoA Mutase/metabolism* ; Acetyl Coenzyme A/metabolism* ; Streptomyces/genetics* ; Polyketide Synthases/metabolism*

Streptomyces are major sources of bioactive natural products. Genome sequencing reveals that Streptomyces have great biosynthetic potential, with an average of 20-40 biosynthetic gene clusters each strain. However, most natural products from Streptomyces are produced in low yields under regular laboratory cultivation conditions, which hamper their further study and drug development. The production of natural products in Streptomyces is controlled by the intricate regulation mechanisms. Manipulation of the regulatory systems that govern secondary metabolite production will strongly facilitate the discovery and development of natural products of Streptomyces origin. In this review, we summarize progresses in pathway-specific regulators from Streptomyces in the last five years and highlight their role in improving the yields of corresponding natural products.
Biological Products ; Multigene Family ; Secondary Metabolism ; Streptomyces/genetics*

Endo-β-N-acetylglucosaminidase is used widely in the glycobiology studies and industries. In this study, a new endo-β-N-acetylglucosaminidase, designated as Endo SA, was cloned from Streptomyces alfalfae ACCC 40021 and expressed in Escherichia coli BL21 (DE3). The purified recombinant Endo SA exhibited the maximum activity at 35 ºC and pH 6.0, good thermo/pH stability and high specific activity (1.0×10⁶ U/mg). It displayed deglycosylation activity towards different protein substrates. These good properties make EndoSA a potential tool enzyme and industrial biocatalyst.
Cloning, Molecular ; Enzyme Stability ; Escherichia coli ; genetics ; Gene Expression ; Mannosyl-Glycoprotein Endo-beta-N-Acetylglucosaminidase ; genetics ; metabolism ; Recombinant Proteins ; genetics ; metabolism ; Streptomyces ; enzymology ; genetics

Constitutively expression of the pathway-specific activators is an effective method to activate silent gene clusters and improve natural product production. In this study, nine shunt products of aminoansamycins (1-9) were identified from a recombinant mutant strain S35-LAL by overexpressed the large-ATP-binding regulator of the LuxR family (LAL) gene aas1 in Streptomyces sp. S35. All the compounds showed no anti-microbial, anti-T3SS and cytotoxic activities.
Biological Products/metabolism* ; Lactams, Macrocyclic/metabolism* ; Multigene Family ; Organisms, Genetically Modified ; Streptomyces/metabolism*

Three new phenazine-type compounds, named phenazines SA-SC (1-3), together with four new natural products (4-7), were isolated from the fermentation broth of an earwig-associated Streptomyces sp. NA04227. The structures of these compounds were determined by extensive analyses of NMR, high resolution mass spectroscopic data, as well as single-crystal X-ray diffraction measurement. Sequencing and analysis of the genome data allowed us to identify the gene cluster (spz) and propose a biosynthetic pathway for these phenazine-type compounds. Additionally, compounds 1-5 exhibited moderate inhibitory activity against acetylcholinesterase (AChE), and compound 3 showed antimicrobial activities against Micrococcus luteus.
Animals ; Anti-Bacterial Agents ; chemistry ; metabolism ; pharmacology ; Bacterial Proteins ; genetics ; metabolism ; Crystallography, X-Ray ; Insecta ; microbiology ; Magnetic Resonance Spectroscopy ; Microbial Sensitivity Tests ; Micrococcus luteus ; drug effects ; Molecular Structure ; Multigene Family ; Phenazines ; chemistry ; metabolism ; pharmacology ; Streptomyces ; chemistry ; genetics ; metabolism

Peach brown rot, caused by Monilinia fructicola, is one of the most serious peach diseases. A strain belonging to the Actinomycetales, named Streptomyces blastmyceticus JZB130180, was found to have a strong inhibitory effect on M. fructicola in confrontation culture. Following the inoculation of peaches in vitro, it was revealed that the fermentation broth of S. blastmyceticus JZB130180 had a significant inhibitory effect on disease development by M. fructicola. The fermentation broth of S. blastmyceticus JZB130180 had an EC₅₀ (concentration for 50% of maximal effect) of 38.3 µg/mL against M. fructicola, as determined in an indoor toxicity test. Analysis of the physicochemical properties of the fermentation broth revealed that it was tolerant of acid and alkaline conditions, temperature, and ultraviolet radiation. In addition, chitinase, cellulase, and protease were also found to be secreted by the strain. The results of this study suggest that S. blastmyceticus JZB130180 may be used for the biocontrol of peach brown rot.
Ascomycota/pathogenicity* ; Bacterial Proteins/metabolism* ; Cell Wall/metabolism* ; Cellulase/metabolism* ; Chitinases/metabolism* ; Fermentation ; Fruit/microbiology* ; Pest Control, Biological/methods* ; Phylogeny ; Plant Diseases/prevention & control* ; Prunus persica/microbiology* ; Siderophores/metabolism* ; Streptomyces/physiology*