27.3.3 Interruption of Protein Oxidation, Membrane Collapse,

and Electron Transport

Protein, cell membrane, and electron transport are important component of bacterial

cell structure, and their smooth functioning is important for cell survival. Protein

oxidation occurred at cellular level, and these modifications lead to functional

changes which disturb the cellular metabolism. The disturbance in electron transport

chain effects the redox reactions which coupled to produce adenosine triphosphate

(ATP). Positive zeta potential on the ENMs plays a crucial role in interaction with

anionic bacterial cell wall which binds strongly to each other and enters the cell

membrane. In this way, it may rupture the cell wall of bacteria and disturb the

electron transport and also oxidize the protein of the cell which results in cell death

(Allaker 2010). Contact of the ENMs to cell also creates different oxidative and

non-oxidative stress to bacterial cell wall which also changes cell physiology and

indorses DNA deprivation (Jayaram et al. 2017). Shi and co-workers found that by

irradiating the light on silver NP, light is absorbed and transfers energy to protein

which is oxidized and gets aggregate protein which leads to cell death (Shi et al.

2019).

Recently, Singh and co-workers used ZnO NPs on D. radiodurans which is an

extremophilic bacteria and can survived in all toughest environment. ZnO NPs tempt

DNA harm and protein oxidation by internalization of ENMs inside the

D. radiodurans cell (Singh et al. 2020). Cadmium oxide was tested against

S. aureus, S. dysenteriae, and P. aeruginosa which shows that on generating ROS

protein leakage is observed from bacterial cell (Azam et al. 2020). Further, interrup-

tion of electron transport and leakage of DNA, protein, and carbohydrate occurred

when ZnO ENMs generates the ROS and damaged the cell wall (Wang et al. 2014).

Chen and co-workers fabricated CuO ENM by a biosynthesized method using soil

borne pathogenic R. solanacearum bacteria which shows that CuO interacts with the

bacterial cell wall and disturbs the ATP synthesis which is followed by cyto-

membrane damage (Chen et al. 2019).

27.3.4 Release of Dissolved Ions

The ability of the dissolved metal ions to interact with bacterial cell is also consid-

ered as a major mechanism for bacterial cell killing. Wang and co-workers studied

the antibacterial effect of NiO and ZnO and α-Fe2O3, γ-Fe2O3, and Fe3O4 ENMs on

photo-bacterium phosphorus bacteria. The effect of these metal oxide particles was

combined with the release of ions which attributed to the antagonistic, synergistic,

and the additive effect of ENMs (Wang et al. 2014). Ag NPs are well studied for the

release of such ions (Ag⁺) which interact with the cell metabolic system by

penetrating the bacterial cell wall. These Ag⁺ ions then damage the DNA of the

cell (Niskanen et al. 2010; Stensberg et al. 2011).

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