Nanomaterials are widely used in biomedical research as drug and antibody carriers, and some nanomaterials have been shown to exhibit antimicrobial activity. Previously, silver nanoclusters (AgNCs) were predicted to interact with the bacterial TolC protein, which is involved in the development of multidrug resistance in pathogens. In this study, glutathione-coated AgNCs were synthesized and characterized. Their toxicological properties were studied in a microplate assay against five bacterial strains, both as single components and in mixtures with heavy metal salts and antibiotics. The resulting AgNCs had a diameter of 2.2 ± 0.5 nm, with excitation and emission maxima of λ = 490 nm and λ = 638 nm, respectively. No significant growth inhibition was observed at the concentrations used in resistance modulation assays (≤2.5 µg/mL Ag), except for transient effects at very high concentrations. A decrease in bacterial resistance to copper (II) and cadmium (II) cations and the antibiotics erythromycin and levofloxacin was observed upon the addition of AgNCs containing 2.5 μg/mL silver to the nutrient medium. A dose-dependent effect of AgNCs on bacterial resistance to toxicants was established. Thus, nanoclusters can be considered as inhibitors of bacterial resistance to heavy metals and antibiotics, which may be useful in studying bacterial adaptation mechanisms and developing technologies for overcoming multidrug resistance in bacteria.

Seven indigenous strains of Bradyrhizobium japonicum subsp. saratovii isolated from soybean nodules (Glycine max (L.) Merr.) grown in the arid Lower Volga region of Russia were investigated. A complete set of the major symbiotic genes was detected in all strains. Single synonymous nucleotide substitutions were identified in nifH and nifD, whereas a missense mutation, Ser149Phe, was found in the nifK gene of strain II-2. Homology modelling showed that this substitution did not cause any noticeable rearrangement of the overall structure of the nitrogenase β-subunit, although it was located near the conserved Cys152 residue. The nodB and nodC genes were completely conserved; the nodC sequence corresponded to symbiovar glycinearum. Structural disruptions in the nap operon were detected in strains II-2 and III-2, which was consistent with the absence of nitrate-reducing activity. Comparison of the genomic data with the inoculation results showed that the most effective strain, II-2, combined strong growth-promoting and yield-enhancing effects with the presence of a complete set of symbiotic genes and disruption of napA. These findings indicate that the integration of genomic analysis with phenotypic assessment improves the accuracy of selecting promising indigenous Bradyrhizobium strains for soybean inoculation.

Orchid plants, due to their high aesthetic qualities of large inflorescences, long flowering period, and ease of care, have high commercial potential; however, when grown industrially in factories, they are susceptible to infectious diseases. In this study, we isolated from Phalaenopsis spp. plants epiphytic, rhizospheric, and endophytic bacteria associated with soft rot symptoms. Twenty-nine isolates exhibiting pectolytic activity were identified as strains of the genera Bacillus, Klebsiella, Microbacterium, Paenibacillus, Paracidovorax, Pseudomonas, and Psychrobacillus based on 16S rRNA analysis. These isolates were tested for their ability to produce cellulase, amylase, sucrase, proteinase, and lipase; to form biofilms; and to exhibit motility (swimming and swarming). Potato microplants under in vitro conditions were used as a model object for initial screening of the strains’ potential phytotoxicity. Most strains were shown to inhibit plant growth, particularly root development. Injection of suspensions of these strains into orchid leaves caused symptoms of soft rot. Thus, we isolated Gram-positive bacteria for the first time from orchid tissues with soft rot symptoms and demonstrated an association of these strains with plant tissue maceration in potato and orchids. Gram-positive bacteria with pectolytic activity are not typical pathogens of orchid soft rot and may require changes in approaches to the monitoring of phytopathogens for this group of plants.