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A novel genistein-producing actinobacterial strain, designated strain CRPJ-33T, was isolated from the healthy leaves of a medicinal plant Xanthium sibiricum collected from Hunan Province, PR China. 16S rRNA gene sequence analysis indicated strain CRPJ-33T belonged to the genus Streptomyces and had 99.7, 99.0, 98.9, 98.9, 98.8 and 98.7% sequence similarities to Streptomyces zhihengii YIM T102T, Streptomyces eurocidicus NRRL B-1676T, Streptomyces xanthochromogenes NRRL B-5410T, Streptomyces michiganensis NBRC 12797T, Streptomyces mauvecolor LMG 20100T and Streptomyces lavendofoliae NBRC 12882T, respectively. Phylogenetic analysis of 16S rRNA gene sequences showed that strain CRPJ-33T was most closely related to S. zhihengii YIM T102T. However, digital DNA–DNA hybridization (dDDH) and average nucleotide identity (ANI) values between them were much less than the recommended threshold values. Furthermore, differential comparisons of the phenotypic characteristics were enough to distinguish strain CRPJ-33T from S. zhihengii YIM T102T. Meanwhile, the ANI and dDDH values or MLSA distances between strain CRPJ-33T and other type strains, which exhibited ≥98.7 % 16S rRNA gene sequence similarities to strain CRPJ-33T, were far away from the recommended threshold values. Based on these results, it is thought that strain CRPJ-33T should represent a novel species of the genus Streptomyces , for which the name Streptomyces genisteinicus sp. nov. is proposed. The type strain is CRPJ-33T (=MCCC 1K04965T=JCM 34526T). In addition, the phenotypic, chemotaxonomic and genotypic characteristics, as well as phylogenetic information revealed that the type strains of S. xanthochromogenes and S. michiganensis should belong to same genomic species. Consequently, it is proposed that S. michiganensis is a heterotypic synonym of S. xanthochromogenes for which an emended description is given.

The search for novel bioactive compounds from the natural environment has been rapidly increased with the increase in multi-drug resistant (MDR) pathogens. In the present study, the antimicrobial potential of novel actinomycetes has been evaluated by initial screening of six soil samples. Primary and secondary screening was performed against Bacillus subtilis, Staphylococcus aureus, Escherichia coli, Candida albicans, Candida tropicalis, Trichophyton rubrum, and other MDR bacterial and fungal test strains, and at the end thirteen active isolates were selected for further study. Microbial strains were identified on the basis of growth conditions and other biochemical characters. Five most active microbial strains were identified using 16S rRNA sequence homology and designated as Streptomyces xanthophaeus MTCC 11938, Streptomyces variabilis MTCC 12266, Streptomyces xanthochromogenes MTCC 11937, Streptomyces levis EU 124569 and Streptomyces sp. NCIM 5500. Four antibacterial and three antifungal compounds isolated from the above five isolates were purified and partially characterized using UV absorption and IR spectra. Two antibacterial metabolites, belong to chromone and peptide antibiotic, respectively. The antifungal compounds were found to be of non-polyene nature. In conclusion, we study the isolation of novel bacterial strains of actinomycetes for producing novel compounds having antibacterial and antifungal activities from the unexplored agro-ecological niches of India. Also, this study paves the way for further characterization of these isolates of Streptomyces sp. for their optimum utilization for antimicrobial purposes.

The impact of microwaves on the germination of spores of Streptomyces xanthochromogenes in a liquid nutrient medium and in a peat soil was studied. The treatment of inoculums with microwave radiation affected the development of the microorganisms from the stage of spore germination to the stage of the formation of microcolonies of actinomycetes upon the spore cultivation in the liquid medium. Typical hypnum-herbaceous peat was used to study the rate of germination of the actinomycetal spores in soil. The study of the dynamics of the Streptomyces xanthochromogenes population in the control soil (without treatment with microwaves) showed that the most active development of the culture took place in the soil moistened to 60% of the maximum water capacity. When the soil was moistened to the minimum adsorption capacity, the streptomyces did not complete their full cycle of development. The stimulation of the spore germination and mycelium growth with microwaves in the soil medium required a longer period in comparison with that for the liquid medium. The stimulation of the spore germination was observed in the liquid nutrient medium in the case of 30-s treatment and in the soil in the case of 60-s treatment.

A novel actinobacterium MBRL 251(T), isolated from a sample collected from a limestone quarry at Hundung, Manipur, India, was characterized using a polyphasic approach. The 16S ribosomal RNA gene sequence of strain MBRL 251(T) showed closest similarities with Streptomyces xanthochromogenes NRRL B-5410(T) (99.6%) and Streptomyces michiganensis NBRC 12797(T) (99.6%). The DNA relatedness between MBRL 251(T) and S. xanthochromogenes NBRC 12828(T), and S. michiganensis NBRC 12797(T) was 46.6% and 40.7%, respectively. Strain MBRL 251(T) contained LL-diaminopimelic acid as the diagnostic diamino acid, with glucose and xylose as the main cell wall sugars, whereas small amounts of galactose, mannose, rhamnose and ribose were also detected in the whole-cell wall hydrolysates. The major fatty acids identified were anteiso-C15:0 (35.1%), iso-C16:0 (21.1%) and anteiso-C17:1 (13.2%). The predominant menaquinones detected were MK-9(H6) and MK-9(H8), whereas the polar lipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylinositolmannosides. The G+C content of the genomic DNA was 72.3%. The phenotypic and genotypic data showed that strain MBRL 251(T) merits the recognition as a representative of a novel species of the genus Streptomyces. It is proposed that the isolate should be classified in the genus Streptomyces as a novel species, Streptomyces hundungensis sp. nov. The type strain is MBRL 251(T) (=JCM 17577(T)=KCTC 29124(T)).

The culture medium of Streptomyces xanthochromogenes JH903 was found to show selective activity against DNA-repair-deficient Escherichia coli CM871 strain. In this report we describe a simple method to locate and isolate DNA binding compounds from the fermentation broth. The method is based on the retention of DNA-reacting compounds in cellulose complexed with DNA, and purification of these compounds with thin-layer chromatography. Screening of microbial metabolites from chloroform extracts of fermentation media resulted in detection of five genotoxic fractions.

The present investigation was aimed to explore in vitro and in silico antimicrobial potential of secondary metabolites produced by terrestrial actinomycetes, S. xanthochromogenes JAR5 isolated from deep forest of Kodaikanal, Tamil Nadu, India and was confirmed by 16S rRNA gene sequencing analysis. The bioactive metabolites produced by the strain JAR5 were obtained from the optimized culture medium through solvent extraction method. The crude extract obtained was purified using silica gel column chromatography and partially purified active elute was characterized using UV, FTIR and GC-MS spectroscopic analysis. The partially purified bioactive metabolites produced by strain JAR5 showed 23.333±0.471 diameter zone of inhibition and minimum inhibitory concentration of 80 μg/ml against Enterococcus sp. In silico molecular docking studies revealed binding into crystal structure of topoisomerase II using Autodock vina 4.2 program. The molecular docking of biological active compounds is in good agreement with in vitro antimicrobial screening where the bioactive metabolites showed effective inhibitory effect against Enterococcus sp.