Growth and Biochemical Responses of Haematococcus pluvialis to Different Arginine Concentrations under Red LED Light

Haematococcus pluvialis is a microalgal species of considerable biotechnological interest due to its outstanding capacity for natural astaxanthin production. However, one of the major constraints limiting astaxanthin productivity in this organism is its relatively slow growth and the resulting low biomass yield. In this study, the time-dependent effects of different concentrations of exogenous L-arginine (0.1, 0.5, and 1.0 mM) on the growth performance and biochemical composition of H. pluvialis cultures were investigated under red LED illumination. Cultures were maintained for 10 days under a 16/8 h light–dark photoperiod at an irradiance of 3000 lux, and optical density (OD₆₈₀) as well as the contents of protein, lipid, astaxanthin, chlorophyll a, and chlorophyll b were determined. The results indicated that red light alone promoted cellular growth and metabolite accumulation only to a limited extent compared with the control. In contrast, supplementation with higher arginine concentrations markedly enhanced growth and substantially altered the biochemical profile of the cultures. The highest optical density and the greatest accumulation of protein, lipid, and astaxanthin were observed in cultures treated with 1.0 mM L-arginine under red light. Similarly, chlorophyll-a and b contents increased in an arginine concentration-dependent manner. Overall, these findings demonstrate that L-arginine supplementation in combination with red-wavelength illumination represents an effective and feasible strategy to improve both biomass formation and, in particular, astaxanthin production in H. pluvialis. This approach may contribute to the development of more sustainable and economically viable cultivation systems for natural astaxanthin production.