Role of Abiotic Stress in Modulating Secondary Metabolite Production in Microalgal Cells

This review highlights the significant capacity of microalgae to produce a wide range of phenolic compounds and other secondary metabolites. It discusses the major abiotic stress factors affecting microalgal cells and their influence on secondary metabolite production and accumulation. Microalgae synthesize numerous bioactive compounds that contribute to their biological significance, such as antimicrobial, antioxidant, and antiviral properties. These biological properties make microalgae promising resources for various applications in pharmaceuticals, functional foods, biofertilizers, biopolymers, and other industrial sectors. Moreover, several abiotic stressors—such as salinity, light intensity, chemical exposure, and heavy metals—have been reported to stimulate the biosynthesis of secondary metabolites in microalgae. These stress conditions are often associated with increased production of protective compounds that help mitigate reactive oxygen species (ROS)-mediated oxidative stress within algal cells. This review also summarizes the impact of abiotic stress on key classes of secondary metabolites, particularly phenolic compounds, carotenoids, and flavonoids, whose concentrations tend to increase under stress conditions. Understanding the relationship between oxidative stress and secondary metabolite biosynthesis in microalgae may provide valuable insights for optimizing their biotechnological and industrial applications.