Stimulating EPA Biosynthesis in <i>Microchloropsis salina</i> through Cultivation with Selected Myxobacterial Culture Supernatants

Microalgae have emerged as a promising and sustainable platform for the production of omega-3 polyunsaturated fatty acids, offering an alternative to fish-derived sources. Among these, <i>Microchloropsis salina</i> (formerly <i>Nannochloropsis salina</i>) is particularly attractive as a candidate due to its naturally high eicosapentaenoic acid (EPA) content. In this study, bacterial supernatants from various myxobacterial strains were evaluated for their ability to enhance microalgal growth and EPA production. Remarkably, the supernatant derived from <i>Nannocystis</i> sp. KYC 2844 significantly improved biomass accumulation when added at 20% (v/v) to f/2 medium, increasing dry cell weight from 1.69 g/l (control) to 2.13 g/l. Although total lipid content decreased from 25.1% to 13.0%, the EPA fraction within the lipid markedly increased from 9.46% to 27.2%. As a result, the overall EPA titer reached 75.5 mg/l, representing a 1.87-fold improvement over the control. Subsequent nutrient analysis revealed that the KYC 2844 supernatant contained 127.3 ppm of ammonium (NH₄⁺), which served as a preferred nitrogen source for <i>M. salina</i> and delayed nitrate utilization. These findings indicate that nitrogen speciation plays a critical role in shaping microalgal lipid profiles. Collectively, this study demonstrates that microbial supernatants can serve as effective medium supplements to enhance both growth and EPA productivity in microalgae and offers a potential strategy for improving the efficiency of microalgal-based omega-3 production systems.