Effects of WS2 Nanosheets on N2-fixing Cyanobacteria: ROS overproduction, cell membrane damage, and cell metabolic reprogramming

The ecotoxicity of tungsten disulfide (WS2) nanomaterials remains unclear so far. Here, the toxicity of WS2 nanosheets on N2-fixing cyanobacteria (Nostoc sphaeroides) was evaluated. Specifically, Nostoc were cultivated in media spiked with different concentrations of WS2 nanosheets (0, 0.05, 0.1 and 0.5 mg/L) for 96 h. Relative to unexposed cells, WS2 nanosheets at 0.5 mg/L significantly decreased cell density, content of total sugar and protein by 10.9 %, 0.43 %, and 6.1 %, respectively. Gas chromatography–mass spectrometry (GC–MS)-based metabolomics revealed that WS2 nanosheets exposure altered the metabolite profile of Nostoc in a dose-dependent manner. Energy metabolism related pathways, including the Calvin-Benson-Bassham (CBB) cycle and tricarboxylic acid (TCA) cycle, were significantly inhibited. In addition, WS2 nanosheets exposure resulted in downregulation (20–40 %) of S-containing amino acids (cystine, methionine, and cysteine) and sulfuric acid. Additionally, fatty acids and antioxidant-related compounds (formononetin, catechin, epigallocatechin, dehydroascorbic acid, and alpha-tocopherol) in Nostoc were drastically decreased by 4–50 % upon exposure to WS2 nanosheets, which implies oxidative stress induced by the nanomaterials. Biochemical assays for reactive oxygen species (ROS) and malondialdehyde (MDA) confirmed that WS2 nanosheets triggered ROS overproduction and induced lipid peroxidation. Taken together, WS2 exposure perturbed carbon (C), nitrogen (N), and sulfate (S) metabolism of Nostoc, which may influence C, N, and S cycling, given the important roles of cyanobacteria in these processes. These results highlight the need for caution in the application and environmental release of WS2 nanomaterials to prevent unintended environmental impacts due to their potential ecotoxicity.