Effect of magnetic field on the growth, productivity and nutritional value of <i>Arthrospira platensis</i>

Arthrospira platensis, a filamentous cyanobacterium, is widely valued in biotechnology for its rapid growth and rich nutritional profile, particularly as a source of single-cell protein (SCP). Static magnetic field (MF) exposure has emerged as a potential non-invasive tool to alter microbial metabolism. However, its effects remain complex and dose-dependent. This study investigates the impact of static magnetic field exposure on the growth, biochemical composition and amino acid profile of A. platensis cultivated in bubble column photobioreactors using Zarrouk’s medium. Magnetic fields were applied using neodymium magnets (~30 mT), and changes in biomass yield, proteins, carbohydrates, lipids, pigments and amino acid composition were assessed. When compared to the control, MF exposure resulted in an increase in final biomass concentration by ~13.2% (4-magnet treatment), protein content by ~46.9% and carbohydrate content by ~16.6%. In contrast, chlorophyll a decreased by ~12.9% and phycobiliproteins showed a consistent decline with increasing magnetic field intensity, while carotenoid content increased by ~16.9%. Amino acid profiling using HRLCMS–QTOF revealed a general decreasing trend in free amino acid abundance with increasing magnetic field intensity, suggesting a potential shift in nitrogen metabolism and intracellular resource allocation. Although total protein content increased, the reduction in free amino acids may indicate enhanced incorporation into structural or functional proteins under magnetic field-induced stress. These findings provide preliminary insights into magnetic field-induced metabolic responses in A. platensis, indicating that MF exposure influences both macro- and micronutrient synthesis. This study lays the foundation for future investigations with higher replication, controlled conditions and advanced analytical validation.