Prevention of Phormidium tenue Biofilm Formation by TiO₂ Photocatalysis

Abstract

We showed that the photocatalytic effect of a coating of TiO₂ greatly reduces the formation of a biofilm by Phormidium tenue (P. tenue), a filamentous cyanobacterium, on glass plates. Sample plates were immersed in P. tenue culture solution (OD₇₃₀=0.3) under concurrent illumination with white fluorescent (WF) and UV light (0.3 mW cm^-2, each) for 11 days. TiO₂-coated glass plates showed greatly reduced adhesion of P. tenue over 11 days compared to bare plates. The number of P. tenue adhering to bare glass plates increased to over 10⁶ cells cm^-2 in 6 days. The photocatalytic anti-biofilm effect was also observed under WF light, although it was small and lasted only a few days. The addition of 1 mM mannitol, a scavenger for the hydroxyl radical (·OH), suppressed the effect. The surface of TiO₂-coated plates was maintained in a highly hydrophilic state for 11 days, regardless of the addition of mannitol. Therefore, we conclude that the photocatalytic oxidation of P. tenue is effective in preventing the formation of a biofilm.