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A bioassay-guided chemical investigation of a bacterium, Streptomyces sp. CMB-MRB032, isolated from sheep feces collected near Bathurst, Victoria, Australia, yielded the known polyketide antimycins A4a (1) and A2a (2) as potent inhibitors of Dirofilaria immitis (heartworm) microfilaria (mf) motility (EC50 0.0013–0.0021 µg/mL), along with the octapeptide surugamide A (3) and the new N-methylated analog surugamide K (4). With biological data suggesting surugamides may also exhibit activity against D. immitis, a GNPS molecular network analysis of a library of microbes sourced from geographically diverse Australian ecosystems identified a further five taxonomically and chemically distinct surugamide producers. Scaled-up cultivation of one such producer, Streptomyces sp. CMB-M0112 isolated from a marine sediment collected at Shorncliff, Qld, Australia, yielded 3 along with the new acyl-surugamides A1–A4 (5–8). Solid-phase peptide synthesis provided additional synthetic analogs, surugamides S1–S3 (9–11), while derivatization of 3 returned the semi-synthetic surugamide S4 (12) and acyl-surugamides AS1–AS3 (13–15). The natural acyl-surugamide A3 (7) and semi-synthetic acyl-surugamide AS3 (15) were shown to selectively inhibit D. immitis mf motility (EC50 3.3–3.4 µg/mL), however, unlike antimycins 1 and 2, were inactive against the gastrointestinal nematode Haemonchus contortus L1–L3 larvae (EC50 > 25 µg/mL) and were not cytotoxic to mammalian cells (human colorectal carcinoma SW620, IC50 > 30 µg/mL). A structure–activity relationship (SAR) study on the surugamides 3–15 revealed that selective acylation of the Lys3-ε-NH2 correlates with anthelmintic activity.

The present study reports the isolation and molecular identification of Streptomyces sp. strain WSN‐2 using 16S rRNA gene sequencing and BLASTn analysis (GenBank Accession No. MN128377), followed by its application in the green synthesis of silver nanoparticles (AgNPs). Biomass filtrate of Streptomyces sp. WSN‐2 efficiently reduced silver ions to form stable AgNPs, confirmed by a characteristic UV‐Vis surface plasmon resonance (SPR) peak at 423 nm. Structural and morphological characterization using FTIR, SEM, TEM, and EDX revealed spherical nanoparticles with a smooth texture and well‐dispersed arrangement. TEM analysis indicated particle size predominantly between 50 and 60 nm (overall range 0.83–100 nm), while the zeta potential of –22.9 mV confirmed moderate colloidal stability. EDX spectra displayed strong elemental silver absorption peaks at 3‐4 keV, indicating crystalline Ag formation. The biosynthesized AgNPs exhibited strong antimicrobial activity against wide range of pathogenic microbes. Maximum antibacterial growth inhibition zones were observed against S. typhi (24 ± 1.53 mm), followed by E. coli (23 ± 1.25 mm), B. subtilis (23 ± 1.73 mm), and P. aeruginosa (22 ± 1.53 mm). Antifungal assays revealed highest antifungal activity against A. flavus (16 ± 1.15 mm), and notable inhibition of A. niger (16 ± 1.25 mm), A. fumigatus (15 ± 1.70 mm), and F. oxysporum (14 ± 1.53 mm). MIC values ranged from 8.00 ± 0.05 µg/mL for P. aeruginosa to 18.000.07 µg/mL for A. fumigatus. The AgNPs also demonstrated remarkable antioxidant potential, achieving 65.2% H₂O₂ scavenging activity at 50 µg/mL, surpassing L‐ascorbic acid (45.1%). These findings highlight Streptomyces sp. WSN‐2 as a promising biogenic source for the synthesis of stable AgNPs with significant antibacterial, antifungal, and antioxidant potential. Green‐synthesized AgNPs from Streptomyces sp. WSN‐2 with robust antibacterial, antifungal, and antioxidant properties, revealing a powerful and eco‐friendly route for producing bioactive nanomaterials.

Ralstonia solanacearum is an important soil-borne bacterial plant pathogen. In this study, an actinomycete strain named NEAU-HV9 that showed strong antibacterial activity against Ralstonia solanacearum was isolated from soil using an in vitro screening technique. Based on physiological and morphological characteristics and 98.90% of 16S rRNA gene sequence similarity with Streptomyces panaciradicis 1MR-8T, the strain was identified as a member of the genus Streptomyces. Tomato seedling and pot culture experiments showed that after pre-inoculation with the strain NEAU-HV9, the disease occurrence of tomato seedlings was effectively prevented for R. solanacearum. Then, a bioactivity-guided approach was employed to isolate and determine the chemical identity of bioactive constituents with antibacterial activity from strain NEAU-HV9. The structure of the antibacterial metabolite was determined as actinomycin D on the basis of extensive spectroscopic analysis. To our knowledge, this is the first report that actinomycin D has strong antibacterial activity against R. solanacearum with a MIC (minimum inhibitory concentration) of 0.6 mg L−1 (0.48 μmol L−1). The in vivo antibacterial activity experiment showed that actinomycin D possessed significant preventive efficacy against R. solanacearum in tomato seedlings. Thus, strain NEAU-HV9 could be used as BCA (biological control agent) against R. solanacearum, and actinomycin D might be a promising candidate for a new antibacterial agent against R. solanacearum.

Background Actinomycetes are gram positive bacteria with high G + C content in their DNA and are capable of producing variety of secondary metabolites. Many of these metabolites possess different biological activities and have the potential to be developed as therapeutic agents. The aim of the present study was to screen actinomycetes inhabiting halophilic environment such as Khewra salt mines present in Pakistan for cytotoxic and antitumor compounds. Results An actiomycetes strain designated as Streptomyces sp. KML-2 was isolated from a saline soil of Khewra salt mines, Pakistan. The strain Streptomyces sp. KML-2 showed 84 % cytotoxic activity against larvae of Artemia salina . In the screening phase, the strain exhibited significant antitumor activity with IC 50 values of 12, 48 and 56 µg/ml against Hela, MDBK and Vero cell lines, respectively. After that extract from 20 l fermentation was used to purify secondary metabolites by several chromatographic techniques. Structure elucidation of isolated compounds revealed that it is highly stable producer of Chromomycin SA (1) and 1-(1 H -indol-3-yl)-propane-1,2,3-triol (2). Both of the isolated compounds showed significant antitumor activity against Hela and MCF-7 cancer cell lines (IC 50 values 8.9 and 7.8 µg/ml against Hela; 12.6 and 0.97 µg/ml against MCF-7, respectively). The 16S rRNA gene sequence (1437 bp) of the strain confirm its identity (99 %) with Streptomyces griseus. Conclusions From this research work we were successful in isolating two potent antitumor compounds, Chromomycin SA and 1-(1 H -indol-3-yl)-propane-1,2,3-triol from Streptomyces KML-2 strain, isolated from Khewra salt mine. As such this is the second report which confirms that S. griseus can produce Chromomycin SA without introducing any mutagenesis in its biosynthesizing gene cluster and isolated indole derivative is being reported first time from any member of actinomycetes group with having novel antitumor activity against Hela and MCF-7 cells. Nucleotide sequences: Nucleotide sequence data reported are available in the GenBank database under the accession number: GenBank KJ009562.

Highlight ResearchThe chitinase production by Streptomyces sp. PB2 was studiedThe critical medium component for chitinase production were identifiedThe optimum medium composition for chitinase production was obtainedMedium optimization improved chitinase production by 6-fold increase in activityAbstractChitin is a polysaccharide compound composed of N-acetylglucosamine (NAG), which is linked by β-1,4-glycoside bonds. In producing NAG from chitin, enzymatic method using chitinase offer advantages compared to chemical degradation. Streptomyces sp. PB2 is a good candidate of chitinase producer which was previously isolated from shrimp pond sediment. However, optimization of chitinase production by Streptomyces sp. PB2 is required for large-scale production of this enzyme. This study aimed to find the optimal medium composition to increase the chitinase enzyme activity of Streptomyces sp. PB2 using the Response Surface Method. Initial screening was done to determine additional carbon and nitrogen sources in colloidal chitin broth suitable for increasing chitinase activity. Optimization of the medium composition was conducted using the Plackett-Burman design to determine the critical components in the colloidal chitin broth medium and continued by Box-Behnken model to optimize the concentration of the medium components. Chitinase activity was obtained by measuring the amount of reducing sugar (NAG) released from enzymatic reaction using DMAB reagent by means of spectrophotometer. The medium components showing high contribution in increasing chitinase activity were K2HPO4, colloidal chitin and peptone, with the confidence level value of 0.66, 0.48, and 0.38, respectively. The Box-Behnken model analysis shows that the combination of K2HPO4 0.007 g/ml, colloidal chitin 1.5 g/ml and peptone 1.5 g/ml in colloidal chitin broth are the optimal medium for Streptomyces sp. PB2, resulted in chitinase activity of 0.0125 U/ml. The increase of 6-fold in chitinase activity was achieved in this study.

Two novel actinomycetes, designated strains 2C-SSA16(2) T and 1C-GS8 T , were isolated from the cuticle of Camponotus japonicus Mayr, collected from Northeast Agricultural University, Heilongjiang Province, north China. Both of them contained genes (involved in antibiotics biosynthesis) of the ketosynthase (KS) and methyl malonyl transferase domains (PKS-I) and the adenylation domain (NRPS). A polyphasic study was carried out to establish the taxonomic positions of these strains. The 16S rRNA gene sequence analysis showed that the two novel isolates 2C-SSA16(2) T and 1C-GS8 T exhibited 98.8% similarity with each other and that they are most closely related to Streptomyces umbrinus JCM 4521 T (99.0, 98.6%), Streptomyces ederensis JCM 4958 T (98.9, 98.7%), Streptomyces aurantiacus JCM 4453 T (98.6, 98.2%), Streptomyces glomeroaurantiacus JCM 4677 T (98.6, 98.1%), Streptomyces tauricus JCM4837 T (98.2, 98.0%) and Streptomyces phaeochromogenes JCM 4070 T (98.2, 99.2%). The corresponding phylogenetic analysis based on partial gyr B gene sequences showed that strains 2C-SSA16(2) T and 1C-GS8 T formed a cluster with the above-mentioned strains. The DNA–DNA hybridization data and phenotypic characteristics indicated that strains 2C-SSA16(2) T and 1C-GS8 T could be readily distinguished from each other and their closest phylogenetic relatives. Therefore, these two strains are suggested to represent two novel species of the genus Streptomyces , for which the names Streptomyces camponoti sp. nov. and Streptomyces cuticulae sp. nov. are proposed. The type strains are 2C-SSA16(2) T (=CGMCC 4.7276 T  = DSM 100522 T ) and 1C-GS8 T (=CGMCC 4.7348 = DSM 103127 T ), respectively.

Microbial enzymes are used as organic catalysts in different industrial processes. In this study, we aimed to produce and investigate alkaline proteases from a novel actinobacterium strain isolated from a Black Sea marine sediment. The optimal production conditions for Streptomyces sp. K47 alkaline proteases was 4-days incubation at 28ºC in a salt-free medium buffered with 50 mM Tris-HCl buffer (pH 9.0) and containing glucose (1.0%, w v-1) and yeast extract (0.5%, w v-1). The enzyme solution was partially purified using (NH4)2SO4 precipitation (40-70%). After desalting, it was purified 1-84 fold with a recovery of 19.42%. Zymogram analyses revealed the presence of more than one protease enzyme. The enzyme solution exhibited maximum activity at pH 9.0 and 37ºC, remaining stable after a 2-hour incubation at all tested conditions. Streptomyces sp. K47 has the potential to be used in industrial processes because of its ability to produce multiple protease enzymes displaying stability in a broad pH and temperature range.

Abstract 3-Methoxy-2-methyl-carbazole-1,4-quinone (1) together with carbazomycins D (2) and F (3) were isolated from the crude extract of Streptomyces CMU-JT005, an actinomycete with nematicidal activity. 3-Methoxy-2-methyl-carbazole-1,4-quinone is reported here for the first time from nature. In this paper, we describe the isolation and structure elucidation of the compounds together with the characterization of the Streptomyces strain CMU-JT005.

Two novel actinomycetes, designated strains ZLN81T and ZLN712T, were isolated from a frozen soil sample which was collected from the Arctic region. Chemotaxonomic and morphological characteristics were found to be typical of members of the genus Streptomyces. Based on 16S rRNA gene sequence analyses, the two strains show high similarity with Streptomyces polygonati NEAU-G9T (99.45%, 99.17%) and Streptomyces yanglinensis 1307T (98.17%, 98.10%). DNA–DNA relatedness between each of the strains and their close phylogenetic neighbours showed that they belonged to distinct species. Multilocus sequence analysis (MLSA) using four housekeeping genes (atpD, gyrB, recA and rpoB) for comparing Streptomyces type strains showed that the MLSA distance of strains ZLN81T and ZLN712T to the closely related species was greater than the 0.007 threshold. The cell wall amino acids of the two strains were identified as alanine, glycine, asparagine, ll-diaminopimelic acid and meso-diaminopimelic acid. The whole cell sugars were identified as galactose and glucose for strain ZLN81T and galactose, glucose and xylose for strain ZLN712T. The predominant menaquinones were identified as MK-10(H8), MK-9(H4) and MK-9(H6) for strain ZLN81T and MK-9(H0), MK-10(H8) and MK-9(H6) for strain ZLN712T. The polar lipid profile of strain ZLN81T was found to contain diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol, phosphatidylinositol mannosides and two unidentified phospholipids, while that of strain ZLN712T consisted of diphosphatidylglycerol, phosphatidylethanolamine, a ninhydrin-positive glycophospholipid, phosphatidylinositol mannosides and two unidentified phospholipids. The major fatty acids were identified as iso-C16:0, anteiso-C17:0, C16:0 and anteiso-C15:0 for strain ZLN81T and iso-C16:0, C16:0, anteiso-C15:0 and iso-C14:0 for strain ZLN712T. The DNA G+C contents were found to be 73.96 and 72.77 mol% for strains ZLN81T and ZLN712T, respectively. On the basis of these phenotypic and genotypic data, strains ZLN81T (= CCTCC AA 2018010T = DSM 107255T) and ZLN712T (= CCTCC AA 2018011T = DSM 107266T) are concluded to represent two novel species of the genus Streptomyces, for which the names Streptomyces polaris sp. nov. and Streptomyces septentrionalis sp. nov. are proposed, respectively.

Abstract The process of solid-state fermentation (SSF) offers a sustainable platform for enzyme production, particularly proteases with industrial relevance. In this study, protease synthesis was investigated using a thermotolerant Streptomyces sp. strain C8, isolated from arid soil of Tamanrasset, Algeria. The strain, Gram-positive with biverticillate spore chains, grew optimally at 45°C, pH 7, tolerated 5% NaCl, and exhibited 93.21% 16S rRNA similarity to Streptomyces griseorubens NBRC 12780 (GenBank accession PV834194), suggesting novelty. Under SSF, various agro-industrial wastes were tested, with spent brewing grains (SBGs) emerging as the most promising substrate. Initial optimization via the One-Factor-at-a-Time approach identified incubation time, temperature, pH, and moisture as critical parameters, yielding maximum activity (82 U/mL) under 30°C, pH 7, 4 days, and 75% humidity. Further optimization using response surface methodology of Box–Behnken design confirmed significant model performance (F = 8.47, P = 0.0003, R² = 0.9081), highlighting moisture, incubation time, and pH as key factors. The refined conditions (31°C, 55% moisture, 3 days, and pH 7) resulted in 128.70 U/mL activity. Overall, these findings demonstrate that low-cost agro-industrial byproducts, particularly SBGs, can serve as efficient, eco-friendly substrates for protease production using thermotolerant Streptomyces strains, offering promising applications in biotechnology. Thermotolerant Streptomyces produces proteases on spent brewing grains.