The current research reports the antibacterial effects of silver (Ag) and citric acid coated iron oxide (Fe 3 O 4 ) NPs on Escherichia coli wild type and kanamycin-resistant strains, as well as on Salmonella typhimurium MDC1759. NPs demonstrated significant antibacterial activity against these bacteria, but antibacterial effect of Ag NPs is more pronounced at low concentrations. Ag NPs inhibited 60–90% of S. typhimurium and drug-resistant E. coli. The latter is more sensitive to Fe 3 O 4 NPs than wild type strain: the number of bacterial colonies is decreased ~ 4-fold. To explain possible mechanisms of NPs action, H + -fluxes through the bacterial membrane and the H + -translocating F O F 1 -ATPase activity of bacterial membrane vesicles were studied. N,N′- Dicyclohexylcarbodiimide (DCCD)-sensitive ATPase activity was increased up to ~ 1.5-fold in the presence of Fe 3 O 4 NPs. ATPase activity was not detected by Ag NPs even in the presence of DCCD, which confirms the bactericidal effect of these NPs. The H + -fluxes were changed by NPs and by addition of DCCD. H 2 yield was inhibited by NPs; the inhibition by Ag NPs is stronger than by Fe 3 O 4 NPs. NPs showed antibacterial effect in bacteria studied in concentration-dependent manner by changing in membrane permeability and membrane-bound enzyme activity. The F O F 1 -ATPase is suggested might be a target for NPs.

Microorganisms have a large number of tools to withstand different, and sometimes strong, environmental stresses, including irradiation, but this ability should be further evaluated for certain applications. Growth inhibition and morphological alterations of Escherichia coli M-17 and Pseudomonas aeruginosa GRP3 wild-type cells caused by UV-A irradiation have been detected in the present study. Comparative analysis was carried out using well-established microbiological methods (determination of specific growth rate, growth lag phase duration, and colony-forming unit number-CFU) and computational approaches, employing light microscopy and digital image analysis to evaluate bacterial cell morphology. Decreases in the specific growth rate, prolonged lag-phases, and lowered CFUs were observed after 5 and 10 min of UV irradiation (approx. 40 Gy) compared to the control (nonirradiated) cells. Accordingly, two computational parameters-the average bacterial cell surface area and the bacterial cell perimeter (i.e., of the 2D projection of bacterial cells in microscopy image)-were reduced. The ratio of bacterial cell surface area (S) to the square of the perimeter (p (2) ) was reduced after 5 min of irradiation, but after 10 min of irradiation the studied bacterial cells became flat cylinders. The revealed findings are concluded to be highly useful in developing new, rapid analysis methods to monitor environmental and UV irradiation effects on bacteria and to detect bacterial cell morphology alterations.

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Abstract-Microorganisms

A novel strain of an iron- and sulfur-oxidizing bacterium was isolated from a natural biotope at Kashen copper ore (Martakert Province, Republic of Artsakh). The strain is able to grow and oxidize ferrous ions in the range of pH 1.4–2.6 with optimal pH 2.0. The optimal temperature for growth is 35°C. Acidithiobacillus sp. Ksh has shown the highest activity for pyrite oxidation among other strains. It also demonstrated high activity in oxidation for copper and copper-gold bearing ores (Armenia). The isolate Acidithiobacillus sp. Ksh was identified as Acidithiobacillus ferrooxidans based on phylogenetic and physiological studies. Comparative studies of EPS production by cells grown on ferrous ions or pyrite were carried out. The chemical composition of capsular and colloidal EPS produced by Acidithiobacillus (At.) ferrooxidans Ksh were revealed to be proteins and carbohydrates. Exosaccharide produced by At. ferrooxidans Ksh is present mainly as polysaccharide in contrast to Leptospirillum (L.) ferriphilum CC, which is oligosaccharide. The structural difference of colloidal particles of these polysaccharides was due to the degree of hydration of the saccharide molecules.