Biosynthesis, characterization, and antimicrobial applications of silver nanoparticles.

In the present study, the strain Brevibacterium frigoritolerans DC2 was explored for the efficient and extracellular synthesis of silver nanoparticles. These biosynthesized silver nanoparticles were characterized by ultraviolet-visible spectrophotometry, which detected the formation of silver nanoparticles in the reaction mixture and showed a maximum absorbance at 420 nm. In addition, field emission transmission electron microscopy revealed the spherical shape of the nanoparticles. The dynamic light scattering results indicated the average particle size of the product was 97 nm with a 0.191 polydispersity index. Furthermore, the product was analyzed by energy dispersive X-ray spectroscopy, X-ray diffraction, and elemental mapping, which displayed the presence of elemental silver in the product. Moreover, on a medical platform, the product was checked against pathogenic microorganisms including Vibrio parahaemolyticus, Salmonella enterica, Bacillus anthracis, Bacillus cereus, Escherichia coli, and Candida albicans. The nanoparticles demonstrated antimicrobial activity against all of these pathogenic microorganisms. Additionally, the silver nanoparticles were evaluated for their combined effects with the commercial antibiotics lincomycin, oleandomycin, vancomycin, novobiocin, penicillin G, and rifampicin against these pathogenic microorganisms. These results indicated that the combination of antibiotics with biosynthesized silver nanoparticles enhanced the antimicrobial effects of antibiotics. Therefore, the current study is a demonstration of an efficient biological synthesis of silver nanoparticles by B. frigoritolerans DC2 and its effect on the enhancement of the antimicrobial efficacy of well-known commercial antibiotics.

Microbacterium panaciterrae sp. nov., isolated from the rhizosphere of ginseng.

Strain DCY56(T) was isolated from a soil sample taken from a ginseng field. The strain was Gram-reaction positive, catalase-positive, oxidase-negative, aerobic and non-motile. Phylogenetic analysis, based on 16S rRNA gene sequence analysis, indicated that strain DCY56(T) belonged to the genus Microbacterium. The closest relatives were Microbacterium azadirachtae AI-S262(T), Microbacterium aerolatum V-73(T) and Microbacterium phyllosphaerae DSM 13468(T) (98.0 %, 98.0 % and 97.5 % gene sequence similarity, respectively). The G+C content of the genomic DNA of strain DCY56(T) was 68.5 mol%. The DNA-DNA relatedness values between strain DCY56(T) and the most closely related type strains were lower than 36 %. The major polar lipids were phosphatidylglycerol, diphosphatidylglycerol and an unidentified glycolipid. The predominant fatty acids contained iso-C16 : 0, anteiso-C15 : 0 and anteiso-C17 : 0. The menaquinones were MK-12 and MK-13. The diagnostic diamino acid of strain DCY56(T) was ornithine. The dominant whole-cell sugars were glucose, rhamnose and ribose. The results of the genotypic analysis, in combination with chemotaxonomic and physiological data, demonstrate that strain DCY56(T) represents a novel species within the genus Microbacterium, for which the name Microbacterium panaciterrae sp. nov. is proposed. The type strain is DCY56(T) ( = KCTC 19884(T) = JCM 17839(T)).

Epilithonimonas ginsengisoli sp. nov., isolated from soil of a ginseng field.

A novel Gram-staining-negative, rod-shaped bacterium, designated DCY78(T), was isolated from soil of a ginseng field in Yeon-cheon province (38° 04' 00″ N 126° 57' 00″ E), Republic of Korea. The phylogenetic analysis based on 16S rRNA gene sequences showed that strain DCY78(T) belonged to the genus Epilithonimonas and was most closely related to Epilithonimonas lactis DSM 19921(T) (98.5 % sequence similarity) and Epilithonimonas tenax DSM 16811(T) (97.8 %). Growth occurred at 10-30 °C with an optimum temperature of 28 °C. The pH range for growth was pH 5.5-8.0. The major polar lipids were found to be phosphatidylethanolamine three unidentified amino lipids and one unidentified polar lipid. The only predominant quinone was MK-6. The major polyamines were sym-homospermidine and spermidine. The major fatty acids were summed feature 3 (comprising C16 : 1ω6c and/or C16 : 1ω7c), iso-C15 : 0 and iso-C17 : 0 3-OH. The DNA G+C content was 37.9 mol%. On the basis of the phenotypic and genotypic analysis, the isolate is classified as representative of a novel species in the genus Epilithonimonas, for which the name Epilithonimonas ginsengisoli is proposed. The type strain is DCY78(T) ( = KCTC 32174(T) = JCM 19896(T)).