Effect of Salinity Stress on Growth, Omega-3 Accumulation, and Desaturase Gene Expression in Spirogyra sp.

Abstract

Salinity is well known to enhance omega-3 biosynthesis in marine algae. However, the effect of salinity on freshwater algae, Spirogyra sp., remains unexplored. This study investigated the effect of salinity on growth, omega-3 accumulation, and desaturase genes, SAD (stearoyl-ACP desaturase), FAD2 (fatty acid desaturase 2), and FAD3 (fatty acid desaturase 3), expression in Spirogyra sp. The Spirogyra sp. was cultivated in Blue Green-11 (BG-11) medium for 12 days using an airlift bioreactor. Salinity stress was applied by adding NaCl in concentrations of 75 mg/L and 125 mg/L, respectively. Biomass was harvested every two days for growth-phase analysis. Omega-3 was quantified by gas chromatography mass spectrometry (GC-MS), while desaturase gene expression was analysed by quantitative reverse transcription polymerase chain reaction. Results showed that 125 mg/L NaCl enhanced growth from 14±0.0 g to 27.10±0.20 g, omega-3 accumulation from 25.87±5.77% to 31.50±14.55%, and expression of FAD3 from 1±0.0 to 4.13 ± 0.28. Correlation analysis showed that FAD3 expression in the exponential phase was strongly related to omega-3 accumulation (ρ = 0.735).  In conclusion, cultivation of Spirogyra sp. with 125 mg/L NaCl improved growth and omega-3 production by enhancing desaturase gene expression, suggesting potential for large-scale use.