The impact of zero-valent iron nanoparticles on a river water bacterial community

Zero-valent iron (ZVI) nanoparticles are of interest because of their many potential biomedical and environmental applications. However, these particles have recently been reported to be cytotoxic to bacterial cells. The overall objective of this study was to determine the impact of 100mg/L ZVI nanoparticles on the diversity and structure of an indigenous river water bacterial community. Response during exposure for 36 days was determined by denaturing gel gradient electrophoresis (DGGE) analysis of bacterial 16S rRNA genes, amplified from extracted DNA, and viable and total cell abundances were determined by plate counting and fluorescent microscopy of DAPI-stained cells. Changes in river water chemistry were also monitored. Addition of ZVI nanoparticles led to a rapid decrease in oxidation-reduction potential (ORP) (+196 to -281 mV) and dissolved oxygen (DO) concentration (8.2-0.6 mg/L), both of which stabilized during the experiment. Interestingly, both viable and total bacterial cell abundances increased and pH decreased, characteristic of an active microbial community. Total community structure was visualized using rank-abundance plots fitted with linear regression models. The slopes of the regression models were used as a descriptive statistic of changes in evenness over time. Importantly, despite bacterial growth, addition of ZVI nanoparticles did not influence bacterial community structure.