Changes in Bacterial Community Structure after Exposure to Silver Nanoparticles in Natural Waters

Silver nanoparticles (AgNPs) are widely used in commercial products as antibacterial agents, but AgNPs might be hazardous to the environment and natural aquatic bacterial communities. Our recent research demonstrated that AgNPs rapidly but temporarily inhibited natural bacterioplankton production. The current study investigates the mechanism for the observed bacterial reaction to AgNPs by examining how AgNPs impact bacterial abundance, metabolic activity (5-cyano-2,3-ditolyl tetrazolium chloride (CTC+) cells), and 16S rRNA community composition. Natural bacterioplankton communities were dosed with carboxy-functionalized AgNPs at four concentrations (0.01-1 mg-Ag/L), incubated in triplicate, and monitored over 5 days. Ionic silver (AgNO3) and Milli-Q water treatments were used as a positive and negative control, respectively. Four general AgNP exposure responses, relative to the negative control, were observed: (1) intolerant, (2) impacted but recovering (3) tolerant, and (4) stimulated phylotypes. Relationships between cell activity indicators and bacterial phylotypes, suggested that tolerant and recovering bacteria contributed the most to the community's productivity and rare bacteria phylotypes stimulated by AgNPs did not appear to contribute much to cell activity. Overall, natural bacterial communities tolerated single, low level AgNP doses and had similar activity levels to the negative control within five days of exposure, but bacterial community composition was different from that of the control.