Bacterial effects and interfacial inactivation mechanism of nZVI/Pd on Pseudomonas putida strain

With the introduction of nano zero valent iron (nZVI) technology into our environment, its potential environmental risk to environmental microorganisms has attracted considerable attention. In this study, Pseudomonas putida was chosen as a typical strain to study the bacterial toxicity of nZVI/Pd. The CFU assay results indicated that nZVI/Pd was toxic to P. putida cells but the toxicity decreased with an increase in DO. The experiments isolated by dialysis bag and flow cytometry analysis suggested that both membrane disruption caused by direct contact and oxidative stress were the main bactericidal mechanisms under the aerobic condition, while membrane disruption resulting from direct contact was the primary bactericidal mechanism in the anaerobic system. Furthermore, according to TEM, SEM, EDS, XRD, FTIR and XPS, it was indicated that in the aerobic system, the reactive oxygen species (ROS) generated by nZVI/Pd could oxidize the amide and hydroxyl groups into carboxyl groups, resulting in a decline in peptides and increase in polysaccharides. In addition, the ROS also accumulated inside the cell and caused cell inactivation via oxidative stress. In the anaerobic system, the adhered nZVI/Pd particles would attack the functional groups such as carboxyl, ester and amide, leading to the decline in proteins and polysaccharides and subsequent damage of the membrane. The findings provide a significant guide for the application of nano-bio combined technology.