We report synthesis of silver nanoparticles (AgNPs) from Streptomyces xinghaiensis OF1 strain, which were characterised by UV–Vis and Fourier transform infrared spectroscopy, Zeta sizer, Nano tracking analyser, and Transmission electron microscopy. The antimicrobial activity of AgNPs alone, and in combination with antibiotics was evaluated against bacteria, namely Escherichia coli, Pseudomonas aeruginosa, Staphylococcus aureus and Bacillus subtilis, and yeasts viz., Candida albicans and Malassezia furfur by using micro-dilution method. The minimum inhibitory concentration (MIC) and minimum biocidal concentration of AgNPs against bacterial and yeast strains were determined. Synergistic effect of AgNPs in combination with antibacterial and antifungal antibiotics was determined by FIC index. In addition, MTT assay was performed to study cytotoxicity of AgNPs alone and in combination with antibiotics against mouse fibroblasts and HeLa cell line. Biogenic AgNPs were stable, spherical, small, polydispersed and capped with organic compounds. The variable antimicrobial activity of AgNPs was observed against tested bacteria and yeasts. The lowest MIC (16 µg ml−1) of AgNPs was found against P. aeruginosa, followed by C. albicans and M. furfur (both 32 µg ml−1), B. subtilis and E. coli (both 64 µg ml−1), and then S. aureus and Klebsiella pneumoniae (256 µg ml−1). The high synergistic effect of antibiotics in combination with AgNPs against tested strains was found. The in vitro cytotoxicity of AgNPs against mouse fibroblasts and cancer HeLa cell lines revealed a dose dependent potential. The IC50 value of AgNPs was found in concentrations of 4 and 3.8 µg ml−1, respectively. Combination of AgNPs and antibiotics significantly decreased concentrations of both antimicrobials used and retained their high antibacterial and antifungal activity. The synthesis of AgNPs using S. xinghaiensis OF1 strain is an eco-friendly, cheap and nontoxic method. The antimicrobial activity of AgNPs could result from their small size. Remarkable synergistic effect of antibiotics and AgNPs offer their valuable potential in nanomedicine for clinical application as a combined therapy in the future.

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This study indicates potential application of biogenic silver nanoparticles as an antimicrobial agent in nanomedicine.

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A genomic-based polyphasic study was undertaken to establish the taxonomic status and biotechnological and ecological potential of a Streptomyces strain, isolate SF28 T , that was recovered from the litter layer in a polish Pinus sylvestris forest. The isolate had morphological characteristics and chemotaxonomic properties consistent with its classi cation in the genus Streptomyces. It formed long straight chains of spores with smooth surfaces, contained LL-diaminopimelic acid and glucose and ribose in whole-organism hydrolysates, produced major proportions of straight, isoand anteisofatty acids, hexa-and octa-hydrogenated menaquinones with nine isoprenoid units and had a polar lipid pattern composed of diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylmethylethanolamine, glycophospholipids and three uncharacterized components. Phylogenetic trees prepared using 16S rRNA gene and multilocus gene sequences of conserved housekeeping genes showed that the isolate formed a branch that was loosely associated with the type strains of several validly published Streptomyces species. A draft genome generated for the isolate was rich in natural product-biosynthetic gene clusters with the potential to produce new specialised metabolites, notably antibiotics, and stress related genes which provide an insight into how they may have adapted to the harsh conditions that prevail in acidic forest soils. A phylogenomic tree based on the genomes of the isolate and its phylogenetic neighbours con rmed that it formed a distinct lineage well separated from its closest evolutionary relatives. The isolate shared low average nucleotide index and digital DNA:DNA hybridization values with its phylogenomic neighbours and was also distinguished from them using a combination of cultural and micromorphological properties. Given this wealth of taxonomic data it is proposed that isolate SF28 T (=DSM 113360 T =PCM 3163 T ) be classi ed in the genus Streptomyces as Streptomyces pinistramenti sp. nov. The isolate showed pronounced antimicrobial activity, especially against fungal plant pathogens.