The effect of silver nanoparticles on the microalgae Haematococcus pluvialis

Abstract

The green alga Haematococcus pluvialis is highly regarded as a producer of astaxanthin. Due to its antioxidant properties, astaxanthin has become a popular nutritional ingredient. Astaxanthin has demonstrated potential pharmacological effects including antidiabetic, anti-inflammatory, and antioxidant activities and cardiovascular and neurological protective properties. Nanoparticles have become integral components of microalgal technologies, serving as stimulators for producing biologically active compounds. The stimulating effect of nanoparticles is based on the induction of oxidative stress. In this study, oxidative stress was induced by silver nanoparticles (AgNPs) and combined with stress from a nutrient-deficient cultivation medium. Citrate-stabilized AgNPs of 10 nm and 20 nm were used. They were applied to the mineral medium from the first day of the cultivation cycle in concentrations ranging from 0.01 mM to 10 mM. The microalgal culture in the red cyst phase was used as the inoculum. The results demonstrated a significant increase of 50-80% in the astaxanthin content in the biomass of the red cysts without altering the biomass content. Additionally, the lipid content in the biomass also increased significantly. The dose/effect relationship between the concentrations of 20 nm AgNPs and astaxanthin values was direct. For 10 nm AgNPs, low concentrations resulted in increased astaxanthin values. Combined stress, with the variable factor being the concentrations of silver nanoparticles, can be proposed as a strategy in the biotechnology of Haematococcus pluvialis for astaxanthin production.