Selenium nanoparticles (SeNPs) can mitigate cadmium (Cd2+) toxicity in crop cultivation and aquaculture. This study investigates the impact of SeNPs on Cd-induced toxicity in Chlamydomonas reinhardtii, a model organism, aiming to mitigate Cd damage in crops. SeNPs were synthesized using sodium carboxymethyl cellulose (CMC) as a dispersant and vitamin C to reduce H2SeO3. Characterization by transmission electron microscopy (TEM) and nanoparticle granulator revealed uniform, stable spherical SeNPs. Cd2+ and SeNPs of varying concentrations were introduced into culture media of wild type (CC125mt+) and cell wall defect type (CC400mt+) Chlamydomonas reinhardtii. Growth curves, photosynthetic pigment content, enzyme activities (T-SOD and CAT), MDA content, and ROS levels were assessed. Fluorescence induction kinetics, QA oxidation kinetics, and Cd2+ content in cells were measured to evaluate SeNPs' effect on Cd toxicity. Results showed SeNPs exacerbated Cd2+ toxicity in CC125mt+ by inhibiting growth and increasing catalase activity, indicating enhanced oxidative damage. SeNPs intensified PSII damage by Cd2+ and increased intracellular Cd2+ content, possibly exacerbating toxicity. SeNPs had no effect on Cd2+ toxicity in CC400mt+. Overall, SeNPs exacerbated Cd2+ toxicity in wild type CC125mt+ but not in cell wall defective CC400mt+. These findings caution against indiscriminate use of nano-selenium to mitigate Cd damage, stressing the importance of careful target selection, dosage, and range considerations.

Selenium nanoparticles (SeNPs) has higher bioavailability and safety than inorganic selenium, and was widely used in medical, agricultural, nutritional supplements, and antibacterial fields. The present study screened a strain L11 producing SeNPs from a selenium rich dairy cow breeding base in Hubei Province, China. The strain was identified as Bacillus subtilis through physiological, biochemical, and molecular biology analysis. Through optimization of cultivation conditions, the optimal cultivation parameters for L11 to produce SeNPs were pH=6, cultivation temperature of 37 °C, 4 mmol/L Na2SeO3, and cultivation for 48 hours. XPS, SEM-EDS, and TEM were used to verify that the Se particles produced by L11 are SeNPs with diameters ranging from 50 to 200 nm. The combination of protein analysis of different cell components and TEM analysis showed that L11 mainly produces SeNPs through the transformation of the cell's periplasmic space, cell membrane, and cell wall. Adding L11 SeNPs complex to sheep feed can significantly enhance the antioxidant activity and immunity of sheep, and increase the Se content in the neck muscles, liver, and spleen tissues.