The growing use of carbon nanotubes (CNTs) in industrial and consumer products raises important questions about their environmental fate and impact on prokaryotes. In the environment, CNTs are exposed to a variety of conditions (e.g. UV light) that could lead to decomposition and changes in their chemical properties. Therefore, the potential cytotoxic effect of both pristine and artificially aged carboxyl functionalized single-walled CNTs at neutral and acidic conditions on Escherichia coli K12 was analyzed using a minimal inhibitory concentration (MIC) assay, which also allowed monitoring of non-lethal growth effects. However, there were no observable MIC or significant changes in growth behavior in E. coli K12 when exposed to pristine or aged CNTs. Exposure to pristine CNTs did not appear to influence cell morphology or damage the cells when examined by electron microscopy. In addition, RNA sequencing revealed no observable regulatory changes in typical stress response pathways. This is surprising considering that previous studies have claimed high cytotoxicity of CNTS, including carboxyl functionalized single-walled CNTs
