Transition between germination and dormancy for non-motile cells of Haematococcus pluvialis: dependence on nitrogen availability through metabolic flux of amino acids and nucleotides

The slow growth and time-consuming cultivation process of Haematococcus pluvialis hinder its large-scale production. Germination of red, non-motile cells presents a novel strategy to improve cultivation efficiency; however, the underlying metabolic adaptations remain poorly understood. This study reveals the regulatory role of nitrogen in the dormancy-to-germination transition. Upon nitrogen supplementation, dormant cells initially reactivated respiration, followed by the restoration of photosynthesis. By contrast, nitrogen deficiency restricted zoospore release and caused carbon accumulation by limited nitrogen assimilation and impaired mitochondrial respiration. Notably, nitrogen deficiency disrupted nucleotide balance by reducing levels of amino acids and purine nucleotides while increasing pyrimidines (uracil, uridine monophosphate, orotate), ultimately impeding DNA replication. Moreover, reactive oxygen species may function as signaling molecules to trigger metabolic reactivation during germination. These findings highlight nitrogen as a central regulator of cell cycle progression in H. pluvialis , offering possible insights into the population dynamics of eukaryotic microalgae with dormant life stages.