Extracellular synthesis of silver nanoparticles by Thiosphaera pantotropha and evaluation of their antibacterial and cytotoxic effects

Abstract

Extracellular biosynthesis of silver nanoparticles (AgNPs) was explored using Thiosphaera pantotropha since this strain exhibits both nitrate-and nitrite-reductase enzyme activity (NaR and NiR, respectively). Optimal AgNP synthesis was achieved using 2 mM AgNO 3 , culture supernatant of nutrient broth grown T. pantotropha, and incubation at 37 °C and 180 rpm. Under these conditions, the localized surface plasmon resonance peak of silver at 404 nm matched well with the average size of the spherical AgNPs based on FEG-TEM micrographs, i.e., 14.6 nm (range: 5-51 nm). The zeta potential of −33.6 mV indicated good stability of the biosynthesized nanoparticles. The XRD spectra demonstrated the simultaneous presence of face-centered cubic crystal structure of AgNPs and AgCl NPs. Ag + ions were possibly reduced by the NaR and NiR enzymes released into the culture media. The FTIR spectra confirmed the stabilization of the AgNPs by biomolecules present in the culture supernatant of T. pantotropha. The synthesized Ag/AgCl NPs exhibited good antibacterial efficacy against both Gram-negative (Escherichia coli and Pseudomonas aeruginosa) and Gram-positive bacteria (Bacillus subtilis and Staphylococcus aureus). The minimum inhibitory concentration (MIC) was 2.5 µg/ml for all the bacteria except B. subtilis (MIC of 10 µg/ml). The minimum bactericidal concentration (MBC) was 2.5, 10, 20, and 5 µg/ml for E. coli, P. aeruginosa, B. subtilis, and S. aureus, respectively. At MBC and higher AgNP concentration, both plating and CLSM imaging confirmed the absence of viable bacteria in treated water. The biogenic AgNPs depicted IC 50 of 34.8 µg/ml for MCF-7 cells.

Green Synthesis of Silver Nanoparticles Using Pecan Nut (Carya illinoinensis) Shell Extracts and Evaluation of Their Antimicrobial Activity

“…It can be observed that all the samples contain AgNPs, since all the samples show a peak within the characteristic wavelength range associated with this type of nanoparticle. Bharti (2020) [ 26 ] reported that, in the case of silver nanoparticles, the plasmon peak appears at a wavelength around 400–450 nm, and its exact position depends on the diameter, shape and size distribution of the nanoparticles.…”

Screening for extracellular synthesis of silver nanoparticles by bacteria isolated from Al-Halfaya oil field reservoirs in Missan province, Iraq

“…The NR enzyme is a NADH-dependent enzyme that accepts two electrons freed via NADH oxidation to reduce nitrate to nitrite. Silver ions (Ag + ) can also be reduced to AgNPs by liberated electrons (Bharti et al 2020).…”

Silver Nanoparticles' Therapeutic Antibacterial, Antiproliferative, and Toxicological Effects.

“…In fact, the natural aquatics ecosystem has a complicated dynamics between its residents, the environment, other nanoparticles, and contaminants, as well as a long-term chemical transformation of the many types of silver at extremely low levels (ng/L to g/L). As a result, more work has to be done to fully understand the environmental and health dangers connected with silver nanoparticles in practical settings (Bharti et al, 2020). Latest evidence, though, demonstrates that silver at concentrations as low as 10 to 102 μg/mL has antimicrobial activity (Ghosh, 2022) Several processes can be used to account for the toxic effects of silver nanoparticles.…”