Selenium Biofortification of Spirulina platensis for Safe and Nutrient-Rich Functional Supplements

Abstract

Spirulina platensis (SP) is a filamentous cyanobacterium widely cultivated as a sustainable source of protein and bioactive compounds. Selenium (Se), an essential trace element with critical roles in antioxidant defense and immune regulation, is often deficient in human diets, including in regions of Turkey. However, inorganic Se supplements have limited bioavailability and safety margins. This study investigated the effects of different sodium selenite concentrations (0, 100, 200, and 500 µg L⁻¹) on the growth, pigment content, and Se enrichment of SP under controlled culture conditions, aiming to identify an optimal strategy for producing Se-biofortified biomass. Growth performance was monitored via optical density, dry cell weight (DCW), specific growth rate (SGR), and biomass productivity (BP). Pigment synthesis, including chlorophyll a (Chl-a) and total phycobiliproteins, was quantified, while Se accumulation was measured in both biomass and culture media by ICP-OES. Moderate Se supplementation (100–200 µg L⁻¹) significantly enhanced growth parameters and biomass yield compared to the control (p < 0.05). The Se-1 treatment (100 µg L⁻¹) yielded the highest SGR (0.0213 day⁻¹), while Se-2 (200 µg L⁻¹) achieved the greatest BP (0.00032 g L⁻¹ day⁻¹). Notably, Se-1 promoted the highest phycobiliprotein content (2.65 mg L⁻¹ at day 30), whereas Se-3 (500 µg L⁻¹) induced elevated Chl-a accumulation but suppressed overall growth, reflecting stress-induced pigment overproduction. Se enrichment in biomass increased dose-dependently, reaching 21, 33, and 102 mg kg⁻¹ in Se-1, Se-2, and Se-3 treatments, respectively. Biomass grown in Se-2 contained ~33 µg Se per gram, allowing a 2 g daily intake to safely deliver 120% of the recommended dietary allowance without exceeding toxicity thresholds. These results demonstrate that SP efficiently converts inorganic Se into bioavailable organic forms while maintaining growth and functional compound content. Cultivation at 200 µg L⁻¹ Se represents an optimal balance between productivity, safety, and enrichment, highlighting SP’s biotechnological potential as a scalable platform for natural, Se-enriched functional foods and nutraceuticals.