Abstract:
Silver nanoparticles (AgNPs) have been commonly used due to their antimicrobial ability, which can inhibit the growth of bacteria. Their uses may lead to their contamination and adverse effects on environmental bacteria, especially bacteria in biofilms. The objective of this study is to investigate the effects of different levels of AgNP concentrations on the biofilm formation, biomass quantity, and EPS composition of Pseudomonas putida KT2440, which is the representative of environmental bacteria used in this study. Biofilm formation was conducted in 96-well plates and 24-well plates under the presence of AgNPs (size distribution of 5-20 nm) at 0, 0.1, 0.5, 1, 10, 50, 100, 500 and 1000 mg/L. The biomass quantity was determined by crystal violet staining. The results showed higher biomass in the biofilms forming under 0.05, 0.1, 0.5 and 1 mg/L for 12-h and 18-h biofilms in the 96-well plates and 24-well plates, respectively, compared with the control (0 mg/L of AgNPs). EPS of biofilms was analyzed using Fourier Transform Infrared Spectroscopy (FT-IR), and the results showed no effect of AgNPs on biofilm chemical compositions. The effect of low AgNP concentrations on the biomass of biofilms was also proved by the observation under the confocal scanning laser microscope (CLSM). The data from this research point out that the low contamination level of AgNPs to the environment might result in the increased formation of biofilms, which requires further studies to determine its effects on the growth rate of other microorganisms in the environment.