Growth bottlenecks of microalga <i>Dunaliella tertiolecta</i> in response to an up-shift in light intensity

Microalgae are a potential source of valuable products including drugs, chemicals, food supplements, biofuels, animal feed and fertilizers. In outdoor culture, biomass productivity is dependent on how well the microalgae respond to fluctuations in light during the day. <i>Dunaliella tertiolecta</i> is a halotolerant, photoautotrophic microalga. Our objective is to identify rate-limiting steps in growth as <i>D. tertiolecta</i> acclimates to changing light intensity. We studied the physiological, metabolic and transcriptomic changes of <i>D. tertiolecta</i> in a low dilution rate chemostat culture to determine rate-limiting processes in cell growth in response to changes in light intensity. Upon a 10-fold increase in light intensity from 40 to 400 µmol photons m^–2 s^–1 (HL), the photosynthetic efficiency and maximum photosynthetic rate (PR) per cell, or per chlorophyll, did not change significantly during lag (2 h) and exponential growth (8 h) phases, which suggests that the photosynthetic system was not the growth rate limiting step in response to higher light intensity. The expression of most genes in 2 h and 8 h samples was similar. Some genes involved in synthesis of cellular structures, protein processing and the cell cycle might be bottlenecks in the HL response, because they were expressed only at 8 h. It might not be practical to increase biomass by genetic modification of <i>D. tertiolecta</i> because of the numerous pathways and genes that are potential bottlenecks. Instead, future research can be directed to improving carbon sequestration by channelling it to storage compounds or excretion as extracellular glycerol.微藻是一类极具潜力的珍贵产物来源，涵盖药物、化工品、食品补充剂、生物燃料、动物饲料与肥料等品类。户外培养场景中，生物质产率取决于微藻对日间光照波动的响应效率。盐生杜氏藻（*Dunaliella tertiolecta*）是一种耐盐光合自养型微藻。本研究旨在明确盐生杜氏藻适应光照强度变化过程中其生长的限速步骤。为探明该藻在光照强度变化下细胞生长的限速过程，本研究通过低稀释率恒化器培养体系，分析了盐生杜氏藻的生理、代谢与转录组变化。当光照强度从40 μmol光子·m⁻²·s⁻¹提升10倍至400 μmol光子·m⁻²·s⁻¹（即高光条件，HL）后，滞缓期（2小时）与指数生长期（8小时）内，单位细胞或单位叶绿素的光合效率与最大光合速率（PR）均无显著变化，这表明光合系统并非高光胁迫下生长速率的限速步骤。2小时与8小时样本中的绝大多数基因表达模式相近。部分参与细胞结构合成、蛋白质加工与细胞周期调控的基因仅在8小时样本中表达，推测它们可能是高光响应过程中的限速瓶颈。由于存在大量潜在的限速通路与基因，通过基因改造盐生杜氏藻以提升生物质产量可能并不具备可行性。未来研究可转向通过将碳代谢导向储存产物或胞外分泌甘油，以提升其固碳能力。