Effect of Pristine Multi-Walled Carbon Nanotubes on Formation and Degradation of Bacterial Biofilms

The effect of pristine multi-walled carbon nanotubes (MWCNT) on the biofilms of gram-negative bacteria, typical members of the activated sludge community, and gram-positive rhodococci involved in xenobiotic biodegradation, was investigated. Nanomaterials of this type not only did not inhibit biofilm formation completely, but were shown to have a probiofilm effect on the studied bacteria. In the presence of MWCNT in dynamic equilibrium with suspension cultures, less massive biofilms of Burkholderia dolosa BOS, Rhodococcus erythropolis 4-1, and R. ruber gt1, but reliably more massive biofilms of Acinetobacter guillouiae 11h, Alcaligenes faecalis 2, and R. erythropolis 11-2 were formed. However, after preliminary cell adhesion and in the absence of suspension culture, all studied strains formed reliably more massive biofilms. More pronounced degradation in the presence of MWCNT was observed for the biofilms of motile gram-negative bacteria. The effect of carbon nanomaterials on the metabolic activity and viability of the studied strains was assessed by reduction of a tetrazolium salt and of the redox indicator resazurin, total ATP content, and cell membrane disturbance. The respiratory activity reliably increased in the biofilms of R. erythropolis 11-2 and R. ruber gt1 grown in the presence of MWCNT, as well as in mature biofilms of R. erythropolis IL BIO and R. erythropolis 11-2 grown in LB medium and then treated with MWCNT. MWCNT were shown to have no negative effect on reduction of metabolized stain XTT by the cells. Comprehensive investigation of biofilm formation and metabolic activity of bacterial cells confirmed the absence of cytotoxic effect of pristine MWCNT on the cells of gram-negative activated sludge bacteria and gram-positive rhodococci in biofilms.