Nano-TiO2 enhances biofilm formation in a bacterial isolate from activated sludge of a waste water treatment plant

• M. caseolyticus with TiO2 NPs under UVA, visible light and dark conditions.
• The reduction in viability was dose and exposure dependent.
• EPS was enhanced with concentration of NPs and exposure conditions.
• Biofilm thickness and density in correlation with the EPS release.

TiO2 NPs is one of the major components of paints and sunscreens and also acts as a catalyst for waste water treatment. The study demonstrates the toxic effects of TiO2 NPs on an anaerobic bacterium, Macrococcus caseolyticus, isolated from the activated sludge of a waste water treatment facility. The cytotoxicity assessment under UVA, visible light, and dark conditions revealed a dose- and exposure-dependent reduction in viability. The examination of cytotoxicity was performed with membrane permeability assessment through LDH (Lactate dehydrogenase) detection. The formation of exopolymeric substances (EPS) was observed to be dose-dependent, and maximum EPS release was noted under UVA condition. The scanning electron microscopy described the aggregation tendency of biofilm to be more pronounced under UVA condition when treated with TiO2 NPs as compared to the control biofilm. Uptake of TiO2 NPs by the biofilm indicated possible remediation of the NPs in waste water by these organisms.