Chlorella vulgaris microalgae as a potential source of vitamins B₁₂ and D₂

The research relevance is determined by the need to summarise current knowledge on the mechanisms of vitamin B₁₂ and D₂ accumulation in Chlorella vulgaris and the factors determining their biochemical variability in microalgae cultures. The study aimed to systematise literature data for 2020-2025 and identify key factors regulating sterol metabolism and vitamin profile in Chlorella vulgaris . The study was based on targeted information search, content analysis, critical comparison, and qualitative synthesis of previous scientific works. Based on the analysis of sources, the study demonstrated that the type of nutrient medium determined the level of micronutrients in the biomass of Chlorella vulgaris . Mineral media provided stable growth but did not contain cobalamin (vitamin B₁₂), while organic substrates – liver extract, whey, permeates, and anaerobic digestates demonstrated a higher potential for cell enrichment due to natural coenzymes, proteins and trace elements. Cobalt ions (Co²⁺) were shown to promote greater accumulation of cobalamin in biomass, while magnesium (Mg²⁺), zinc (Zn²⁺), iron (Fe²⁺/Fe³⁺) and copper (Cu²⁺) were substantial cofactors for enzymes and transport systems that influenced sterogenesis. Regarding vitamin D₂ (ergocalciferol), the literature confirmed the decisive role of ultraviolet radiation in the B range (UV-B), which initiated the photoconversion of ergosterol. The intensity and spectral composition of light determined the rate of sterol accumulation, while salinity, nitrogen or phosphorus deficiency, and other stress factors contributed to increased lipidation and changes in the sterol pool. The study determined that in the stationary phase of the culture, lipid and sterol fractions accumulated more intensively than during the period of active cell division. A generalised analysis of sources showed that the most effective enrichment of Chlorella vulgaris with vitamins B₁₂ and D₂ is achieved by combining organic nutrient media, an optimised lighting spectrum with a UV-B component, and a controlled mineral composition of the medium