Low Concentrations of Silver Nanoparticles and Silver Ions Perturb the Antioxidant Defense System and Nitrogen Metabolism in N₂-Fixing Cyanobacteria

Abstract

Although toxic effects of silver nanoparticles (AgNPs) on aquatic organisms have been extensively reported, responses of nitrogen-fixing cyanobacteria to AgNPs/Ag + under environmentally relevant concentrations are largely unknown. Here, cyanobacteria were exposed to different concentrations of AgNPs (0.01, 0.1, and 1 mg/L) or Ag + (0.1, 1, and 10 μg/L) for 96 h. The impacts of AgNPs and Ag + on photosynthesis and N 2 fixation in cyanobacteria (Nostoc sphaeroides) were evaluated. In addition, gas chromatography−mass spectrometry (GC−MS)-based metabolomics was employed to give an instantaneous snapshot of the physiological status of the cells under AgNP/Ag + exposure. Exposure to high doses of AgNPs (1 mg/L) or Ag + (10 μg/L) caused growth inhibition, reactive oxygen species overproduction, malondialdehyde accumulation, and decreased N 2 fixation. In contrast, low doses of AgNPs (0.01 and 0.1 mg/L) and Ag + (0.1 and 1 μg/L) did not induce observable responses. However, metabolomics revealed that metabolic reprogramming occurred even at low concentrations of AgNP and Ag + exposure. Levels of a number of antioxidant defense-related metabolites, especially phenolic acid and polyphenols (gallic acid, resveratrol, isochlorogenic acid, chlorogenic acid, cinnamic acid, 3-hydroxybenzoic acid, epicatechin, catechin, and ferulic acid), significantly decreased in response to AgNPs or Ag +. This indicates that AgNPs and Ag + can disrupt the antioxidant defense system and disturb nitrogen metabolism even at low-dose exposure. Metabolomics was shown to be a powerful tool to detect "invisible" changes, not observable by typical phenotypic-based endpoints.

MoS2 Nanosheets–Cyanobacteria Interaction: Reprogrammed Carbon and Nitrogen Metabolism

“…In addition, our previous study found that antioxidant related metabolites, such as phenolic acids and polyphenols, are very sensitive to environmental stressors. For example, Ag NPs at 0.1 mg/L resulted in a considerable decrease of antioxidant compounds . In contrast, all of the detected antioxidants in Nostoc , including catechin, 4-hydroxycinnamic acid, resveratrol, 1,2,4-benzenetriol, epicatechin, pelargonic acid, 3,4-dihydroxycinnamic acid, chlorogenic acid, and α-tocopherol, were unaffected upon MoS 2 exposure (data not shown).…”

“…For example, Ag NPs at 0.1 mg/L resulted in a considerable decrease of antioxidant compounds. 27 In contrast, all of the detected antioxidants in Nostoc, including catechin, 4-hydroxycinnamic acid, resveratrol, 1,2,4-benzenetriol, epicatechin, pelargonic acid, 3,4-dihydroxycinnamic acid, chlorogenic acid, and α-tocopherol, were unaffected upon MoS 2 exposure (data not shown). This indicates that MoS 2 had limited impacts on oxidative stress in Nostoc, which is consistent with the above-mentioned data on MDA and the growth rate.…”

Changes in primary metabolites and volatile organic compounds in cotton seedling leaves exposed to silver ions and silver nanoparticles revealed by metabolomic analysis

“…Previous studies showed that ionic silver induced more toxic effects than AgNPs in green algae. Low concertation Ag + induced more significantly changed metabolites than AgNPs in N 2 -fixing cyanobacteria ( Huang et al, 2020 ). In this experiment, the changes in the metabolic profiles of the Ag + group was greater than that in the AgNP group, which may be because Ag + from AgNO 3 is more available than Ag + from AgNPs.…”

Oxygen‐Vacancy‐Mediated ROS Generation Mechanism of MgO Nanoparticles against Escherichia coli

“…After MgO 650 treatment, the fluorescence intensity of E.coli suspension was 9 times higher than that of the control group, suggesting that MgO 650 with abundant oxygen vacancies could induce overproduction of ROS and increase the ROS level in E. coli, thus resulting in the damage of the antioxidant defense system. [40] Additionally, the contribution of single ROS ( * O 2 À , * OH and H 2 O 2 ) to the antibacterial effect of MgO 650 was investigated by the ROS scavenging test. In Figure S3 (Supporting Information Summary), the SOD, CAT and D-mannitol had minimal impact on the number of E. coli colonies, suggesting that addition of the scavenger had almost no influence on the antibacterial activity, in accordance with previous reports.…”