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Silver nanoparticles (Ag NPs) represent one of the most widely employed metal-based engineered nanomaterials with a broad range of applications in different areas of science. Plant extracts (PEs) serve as green reducing and coating agents and can be exploited for the generation of Ag NPs. In this study, the phytochemical composition of ethanolic extract of black currant (Ribes nigrum) leaves was determined. The main components of extract include quercetin rutinoside, quercetin hexoside, quercetin glucuronide, quercetin malonylglucoside and quercitrin. The extract was subsequently employed for the green synthesis of Ag NPs. Consequently, R. nigrum leaf extract and Ag NPs were evaluated for potential antibacterial activities against Gram-negative bacteria (Escherichia coli ATCC 25922 and kanamycin-resistant E. coli pARG-25 strains). Intriguingly, the plant extract did not show any antibacterial effect, whilst Ag NPs demonstrated significant activity against tested bacteria. Biogenic Ag NPs affect the ATPase activity and energy-dependent H+-fluxes in both strains of E. coli, even in the presence of N,N’-dicyclohexylcarbodiimide (DCCD). Thus, the antibacterial activity of the investigated Ag NPs can be explained by their impact on the membrane-associated properties of bacteria.

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The photodependent production of hydrogen (H2) as a promising source of renewable energy is currently of great interest. Green algae carry out photoproduction of H2 associated with electron transport during photosynthesis and catalyzed by [Fe]-hydrogenase, which is sensitive to oxygen and is inactivated by water photolysis. The issue of incompatibility between water photolysis and hydrogenase can be solved by creating deprivation of nutrients such as nitrogen and sulfur. The results have shown that H2 generation by Chlorella vulgaris Pa-023 is stimulated 2.5 times by sulfur deprivation and 2.7 times by nitrogen deprivation compared to algae grown on a complete Tamiya medium. The use of a specific inhibitor of PS II, DCMU (3-(3,4-dichlorophenyl)-1,1-dimethylurea), demonstrated that during nutrient deprivation in algae operates a PS II-dependent pathway of H2 generation. Thus, sulfur and nitrogen deprivation stimulates photoproduction of H2 by C. vulgaris.