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Silver nanoparticles (AgNPs) have been extensively investigated for their biostimulatory or toxic effects on microalgae. However, the influence of the inoculum’s developmental stage on astaxanthin biosynthesis in the microalga Haematococcus pluvialis remains largely unexplored. This study aimed to assess the effects of AgNPs on biomass and astaxanthin production in Haematococcus pluvialis by comparing cultures initiated with two distinct inoculum types: green vegetative cells and aplanospores. Experimental cultures were exposed to silver nanoparticles of 40 and 60 nm, each applied at five concentrations (from 0.01 to 1.0 mg/L). Biomass and astaxanthin content were quantified to evaluate the metabolic responses induced by AgNPs exposure. Both inoculum types exhibited a similar response profile: exposure to 40 nm AgNPs did not induce astaxanthin synthesis at any tested concentration. When astaxanthin was determined in the aplanospore stage, the green-cell inoculum showed inhibited accumulation at all concentrations, with over a 20% reduction, while the aplanospore inoculum-maintained control levels. For 60 nm AgNPs, final astaxanthin content in Haematococcus pluvialis cultures with green motile cell inoculum increased by 8.7–13.3%, mainly at higher concentrations. With the aplanospore inoculum, red-stage astaxanthin increased by 50–80% at all concentrations. A slight reduction in biomass was observed in green-cell cultures treated with 40 nm AgNPs, while aplanospore-based cultures maintained more stable biomass growth. The results underline the critical role of the inoculum’s developmental stage in modulating the metabolic response of Haematococcus pluvialis to AgNPs and provide a foundation for optimizing astaxanthin yield through nanoparticle-assisted cultivation strategies.
Keywords: Haematococcus pluvialis, silver nanoparticle, inoculum stage, biomass, astaxanthin© This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.