Characteristics of energy distribution for N, P and C sequestration by Microcystis aeruginosa under blue and orange light

Investigating the mechanisms of cyanobacterial bloom is a crucial topic in the field of bloom control. Previous studies showed that orange light promotes cyanobacteria growth, whereas blue light increases the production of phycobiliprotein. But the underlying mechanisms remain inadequately understood. In this study, Microcystis aeruginosa (FACHB-905) was cultured on different nitrogen and phosphorus concentrations under blue, orange, and white LED light. The researchers measured growth rates, nutrient uptake rates, and key enzyme activities to investigate the effect of light quality on nutrient uptake and energy distribution. The results showed that M. aeruginosa grew faster under orange light, with higher glutamine synthetase (GS) (1.39 ×10⁻⁷ U·cell⁻¹), H⁺-ATPase (3.31 ×10⁻⁷ μ·mol·h⁻¹·cell⁻¹) activity, but low carbon fixation efficiency (0.017 mg·L⁻¹·d⁻¹·cell⁻¹). Under blue light, the growth rate was the lowest, the activities of carbonic anhydrase (CA) (3.15 ×10⁻⁶ EU·cell⁻¹) and carbon fixation efficiency (0.076 mg·L⁻¹·d⁻¹·cell⁻¹) were highest. GS activity (1.19 ×10⁻⁷U·cell⁻¹) and nitrite reductase (NR) activity (0.06 ×10⁻⁴ nmol·h⁻¹·cell⁻¹) were the lowest. Under white light, the activities of NR (0.63 ×10⁻⁴ nmol·h⁻¹·cell⁻¹), GS (1.58 ×10⁻⁷ U·cell⁻¹), and H⁺-ATPase (4.12 ×10⁻⁷μ·mol·h⁻¹·cell⁻¹) were highest, carbon fixation efficiency (0.057 mg·L⁻¹·d⁻¹·cell⁻¹) was lower. These results suggested that the energy absorbed by photosynthesis is primarily used for the NH₄⁺ absorption process under orange light, mainly for carbon sequestration under blue light, and mainly for NO₃⁻ uptake under white light. Our results indicated that orange light can promote the growth of M. aeruginosa by enhancing its nitrogen uptake, while blue light can increase its carbon sequestration.