Photocatalytic disinfection of spoilage bacteria Pseudomonas fluorescens and Macrococcus caseolyticus by nano-TiO2

Abstract

Photocatalytic disinfection of gram-negative (G−) Pseudomonas fluorescens and gram-positive (G+) Macrococcus caseolyticus spoilage bacteria by nano-TiO2 under different experimental conditions and its disinfection mechanism were investigated. The disinfection mechanism was determined by the release of cellular K+, lipid oxidation, and the TEM morphological images. Photocatalytic treatments showed the similar effects on both G− and G+ bacteria regardless of experimental conditions and disinfection mechanism. The lower the initial bacterial population was, the shorter the time that was required to eliminate the bacteria. Increased TiO2 contents and light intensity resulted in increased bacterial killing. Both K+ leakage and lipid oxidation increased significantly after the TiO2 treatment. Electronic images illustrate that bacterial cells started showing damages in cell walls and membranes after 30 min treatment, cytoplasm leakage after 90 min treatment, and lysis after 150 min treatment. The greater reduction population of M. caseolyticus was observed than that of P. fluorescens. These results demonstrate that effectiveness of nano-TiO2 depends on the initial bacterial population, TiO2 content, and UVA light intensity. TiO2 treatments results in increased lipid peroxidation and damaged cell membrane integrity before cell death. G+M. caseolyticus is more susceptible to photocatalytic disinfection by nano-TiO2 under light than G−P. fluorescens regardless of experimental conditions.