Effect of culture medium on the extracellular synthesis of silver nanoparticles using Klebsiella pneumoniae, Escherichia coli and Pseudomonas jessinii

Because green biosynthesis using microorganisms is advertised as a promising, eco-friendly and biocompatible approach for the production of silver nanoparticles (AgNPs), many studies were focused on the extracellular production of nanoparticles enabling an easy downstream processing. However, the influence of the culture media on extracellular AgNP synthesis was rarely investigated. In this study, the effect of various culture media and their components on the extracellular AgNP synthesis of Klebsiella pneumoniae UVHC5, Escherichia coli ATCC 8739 and Pseudomonas jessinii UVKS19) was investigated. UV-Vis spectroscopy, DLS, SEM and EDX spectroscopy were used to verify the particles formed. Culture media, bacterial supernatants and the individual medium components were added to AgNO3 solutions. After 7 days of incubation the liquids contained particles of different shapes, sizes and composition. The formation of specific particle species mainly depended on the composition of the culture media (especially the Cl- content), in which the bacteria were inoculated. Samples incubated with bacterial supernatant of STI, NB, LB or MH showed AgCl particles of cubic or star-/flowerlike shapes coated with AgNPs. In contrast, silver nanoclusters were observed in the inoculants of bacterial supernatants grown in MRS or AgNPNB. However, small effects of bacterial metabolites on the formation of the particles could be observed and indicate an influence of the media alteration by bacterial growth on the particle formation. When the individual medium components were added to AgNO3, different absorbance spectra were obtained. Therefore, we conclude that the formation of Ag/AgCl nanoparticles results from the interaction of all medium components.