AgNPs biosynthesized from Pseudomonas Z9.3 metabolites as antimicrobial agents against bacterial and fungal pathogens

Svitlana Plokhovska ^1,2* Elena Fuente-González ¹ Enrique Gutierrez-Albanchez ¹ Francisco-Javier Gutierrez-Mañero ¹ Beatriz Ramos-Solano ^1*

• ¹ Faculty of Pharmacy, Universidad San Pablo-CEU Universities, Madrid, Spain
• ² Institute of Food Biotechnology and Genomics NAS of Ukraine, Kyiv, Ukraine

An eco-friendly method for the biosynthesis of functional silver nanoparticles (AgNPs) using plant growth promoting bacteria (PGPB), in particular Pseudomonas sp. Z9.3, has been developed. The influence of physicochemical parameters (temperature, pH and concentrations of AgNO3) on the synthesis of AgNPs was studied, setting two optimal physicochemical conditions at 37 °C, pH 9, and a 5:1 ratio of bacterial supernatant to 5 mM AgNO3(S1-9) and 37 °C, pH 7, and a 2:4 ratio (S4-7). The formation of AgNPs was confirmed by UV-visible spectroscopy with an absorption range between 400 and 450 nm. The SEM and TEM analysis showed the spherical shape of AgNPs with a good distribution of nanoparticles and the average size ranged from 8.24 ± 0.26 to 13.32 ± 0.4 nm. Antibacterial activity against different pathogenic bacteria and fungi was tested. Antibacterial activity of AgNPs against 6 human pathogens and 3 phytopathogens was evaluated. The antibacterial potential of S1-9 against Gram-negative strains was lower than against Gram-positive strains; in particular, S. epidermidis was the most sensitive (93.76 %) compared to the equivalent concentration of Ag. In the case of fungi, S4-7 exhibited better inhibitory activity compared to the negative control. The highest dose (120 ppm) of S4-7 AgNP inhibited fungal growth being the most sensitive Alternaria sp. (74.97 %), followed by Stemphylium sp. (66.30 %), Fusarium sp. (45.62 %) and Rhizopus sp. (32.68 %).