Toxic Effects of Single-Walled Carbon Nanotubes in the Development of E. coli Biofilm

The impact of single-walled carbon nanotubes (SWNTs) on the different developmental stages of biofilms has been investigated using E. coli K12 as a model organism. Specifically, we investigated (i) the impact of SWNT concentration on cell growth and biofilm formation, (ii) toxic effects of SWNTs on mature biofilms, and (iii) formation of biofilm on SWNT-coated surfaces. The results show that at the initial stage of biofilm formation, SWNTs come into contact with bacterial cells prior to biofilm maturation and inhibit their growth. Furthermore, the results suggest that bacteria in mature biofilms are less sensitive to the presence of SWNTs than cells in other biofilm stages, similar to previous observations of biofilm resistance to antimicrobials. In mature biofilms, the soluble exopolymeric substances (EPS) secreted by the biofilm play an important role in mitigating the toxic effects of SWNTs. Upon exposure to SWNTs, biofilms without soluble EPS in the supernatant had a much more significant loss of biomass because of cell detachment from the biofilm than biofilms containing soluble EPS. To observe similar cell loss, biofilms with soluble EPS needed SWNT concentrations that were 10 times higher compared to biofilms without soluble EPS. Finally, SWNTs deposited onto surfaces affected significantly the subsequent biofilm development. Analysis of the total biomass and the area occupied by cells indicates that a SWNT-coated substratum has 10 times less biofilm colonization and biomass production than a control substratum without SWNTs.