Evidence for Compression ofEscherichia coliK12 Cells under the Effect of TiO₂Nanoparticles

Abstract

It has been shown that treatment with titanium dioxide nanoparticles (TiO2 NPs) combined with near-ultraviolet (UV-A) irradiation or in certain dark conditions reduced the numbers of various microorganisms, but the mechanism of this effect remains unclear. In this study to further clarify the mechanism of the antibacterial effect of TiO2 NPs the physiological state of E. coli K12 cells was estimated after incubation with the NPs (0.2 g/L) for different periods of time, with or without UV-A irradiation. Cell incubation with TiO2 NPs, combined or not combined with UV-A irradiation, showed that inactive cells were located only within cell aggregates formed after incubation with TiO2 NPs and that the larger the aggregate, the greater the number of such cells. When the formation of large aggregates was prevented, exposure to NPs under UV-A irradiation failed to result in cell inactivation. A comparative analysis of fluorescence and optical microscopic images of the same aggregates showed that the location of inactivated cells coincided with the zone of increased optical density within the aggregate. After treatment with TiO2 NPs under UV-A for 30, 60, or 120 min cells within the aggregates were the first to be inactivated. Cells on which NPs irradiated more strongly (at the periphery of large aggregates and single) remained active for a longer time than cells within the aggregates. As the time of treatment increased, so did the degree of cell compaction, with some zones of the aggregates eventually transforming into an acellular mass. After UV-A irradiation the cell aggregates spontaneously moved toward each other and gradually fused into larger structures, indicating that such exposure enhanced mutual attraction of cells treated with the NPs. Present study provides evidence for hypothesis that bacterial cells covered with TiO2 NPs are inactivated due to their mutual attraction and consequent compression.

Antibacterial Metal Oxide Nanoparticles: Challenges in Interpreting the Literature

“…Of particular concern in the NP literature is the use of bacterial strains which are not typically considered pathogenic or of industrial significance. The most common are K12 strains of E. coli which are commonly used in molecular biology laboratories as expression or cloning vectors(60, 61). Although these strains are convenient, they are engineered strains and typically lack many of the highly evolved and redundant defense mechanism of true pathogens.…”

The antimicrobial activity of nanoparticles: present situation and prospects for the future

“…Iron can also cause bacterial cell decomposition, 114 and NPs can cause bacterial cells to aggregate, resulting in inactivation due to compression. 115 Physical damage of bacterial membranes is the most important mechanism of the antibacterial activity of graphene. Tu et al 116 investigated the antibacterial molecular mechanisms of graphene nanosheets against E. coli.…”

“…TiO 2 NPs allow bacterial DNA compression, degeneration, and fragmentation, thereby reducing the physiological activity of genes. 115 The affinity and binding mode of nanotitanium dioxide and DNA were predicted by molecular docking, which indicated that TiO 2 NPs targeted DNA rich in G-C. 130 In addition, whole-genome analysis can be used to characterize the molecular mechanisms of bacterial apoptosis.…”

Simultaneous bacterial inactivation and degradation of an emerging pollutant under visible light by ZnFe2O4co-modified with Ag and rGO

“…The complete inactivation of bacteria in -Ag/rGO NC was also carried out to distinguish the bacterial inactivation caused by the physical contact from that caused by the photocatalytic process. 38 The log reduction of only 1.5 in 60 min during the dark control experiment clearly states that the bacterial inactivation is actually a photocatalytic process and not just due to physical contact with NC. The enhanced photocatalytic properties of ZnFe 2 O 4 -Ag/rGO as compared to those of ZnFe 2 O 4 and ZnFe 2 O 4 /rGO can be attributed to the increased surface area and better charge generation and separation due to the presence of rGO and Ag NPs.…”