The effect of TiO2 nanoparticles on sulfate-reducing bacteria and their consortium under anaerobic conditions

Abstract

Sulfate-reducing bacteria are one of the most commonly occurring strains in industrial and waste water samples. TiO2 NPs (titanium dioxide nanoparticles) are an important component of cosmetics and toothpastes and are also useful agents as disinfectants in treatment of wastewater. The study delineates the effect of TiO2 NPs on sulfate-reducing bacteria (Desulphovibrio desulfuricans and Desulfotomaculum nigrificans) and their consortium. The specific growth of these bacteria under UVA, visible light, and dark was found to be exposure dependent. With an increase in the concentration of TiO2 NPs, insignificant changes were observed in the sulfate reduction rate. The specific growth rate of bacteria was reduced upon exposure of 1μg/mL of TiO2, whereas lower concentrations did not have any significant impact. The exopolymer release, which is indicative of the bacterial defense response, demonstrated a nanoparticle exposure-dependent increase over time, and it was significantly higher in the consortium as compared to individual strains. Similarly, the biofilm thickness and density showed a linear dependence on the NP exposure time. The surface chemical changes of exopolymers were analyzed with help of FT-IR analysis. Distortion of the consortium cells embedded within the biofilm matrix when exposed with the highest exposure dose of NPs and UV was prominent as compared to control cells. The consortium demonstrated enhanced ability to counter stress under all the experimental conditions as compared with the single bacterial strains. The sulfate-reducing potency of these bacteria under low exposure concentrations of TiO2 NPs could be used as a bioremediation tool in wastewater treatment plants.