Size-dependent cytotoxicity of silver nanoparticles to Azotobacter vinelandii: Growth inhibition, cell injury, oxidative stress and internalization

Abstract

The influence of nanomaterials on the ecological environment is becoming an increasingly hot research field, and many researchers are exploring the mechanisms of nanomaterial toxicity on microorganisms. Herein, we studied the effect of two different sizes of nanosilver (10 nm and 50 nm) on the soil nitrogen fixation by the model bacteria Azotobacter vinelandii. Smaller size AgNPs correlated with higher toxicity, which was evident from reduced cell numbers. Flow cytometry analysis further confirmed this finding, which was carried out with the same concentration of 10 mg/L for 12 h, the apoptotic rates were20.23% and 3.14% for 10 nm and 50 nm AgNPs, respectively. Structural damage to cells were obvious under scanning electron microscopy. Nitrogenase activity and gene expression assays revealed that AgNPs could inhibit the nitrogen fixation of A. vinelandii. The presence of AgNPs caused intracellular reactive oxygen species (ROS) production and electron spin resonance further demonstrated that AgNPs generated hydroxyl radicals, and that AgNPs could cause oxidative damage to bacteria. A combination of Ag content distribution assays and transmission electron microscopy indicated that AgNPs were internalized in A. vinelandii cells. Overall, this study suggested that the toxicity of AgNPs was size and concentration dependent, and the mechanism of antibacterial effects was determined to involve damage to cell membranes and production of reactive oxygen species leading to enzyme inactivation, gene down-regulation and death by apoptosis.

Advancements in Plant and Microbe-Based Synthesis of Metallic Nanoparticles and Their Antimicrobial Activity against Plant Pathogens

“…DNA damages, such as mutations, deletions, single-strand breaks, double-strand breaks, and cross-linking with proteins, may occur [168]. Zhang et al revealed that damaging cell membrane and generating ROS are involved in the antibacterial mechanisms [169]. They observed damage of cell membrane and AgNPs inside Azotobacter vinelandii cells using TEM and revealed AgNP-induced hydroxyl radicals inside bacterial cells using electron spin resonance.…”

Understanding gold toxicity in aerobically-grown Escherichia coli

“…Currently, nanostructures (NS) containing some of these non-essential metals are used in diverse applications such as water treatment, photocatalysis, optics and therapeutic procedures, among others [5,17]. In particular, gold nanostructures (AuNS) behave as potent antimicrobial agents against multidrug resistant Gram-negative and Gram-positive bacteria [18].…”

“…In particular, gold nanostructures (AuNS) behave as potent antimicrobial agents against multidrug resistant Gram-negative and Gram-positive bacteria [18]. In general, it has been suggested that AuNS would be toxic because they can generate ROS, similar to that seen in many other antibacterial materials such as ZnO, TiO 2 and Ag nanoparticles (NPs) [17,19,20]. Other targets depend on the route of gold(III) complexes synthesis or composition; for instance, AuNPs covered with organic molecules such as 4,6-diamino-2-pyrimidinethiol produce i) a change in membrane potential that limits ATPase activity and ii) inhibit tRNA binding to the ribosome, thus leading to a collapse of several biological processes without ROS production [21].…”

Novel Bioactive and Therapeutic Root Canal Sealers with Antibacterial and Remineralization Properties

“…The adherence of silver ions to the bacterial cell wall can also cause cell wall destruction and release of essential cellular components [41]. Due to the high affinity of silver to sulfur, nitrogen and oxygen, silver ions can bind to sulfhydryl groups in proteins and cause protein denaturation or bind to N atoms from nucleic acids and prevent DNA replication [42].…”