Cyanobacteria use a carbon dioxide (CO₂)-concentrating mechanism (CCM) that enhances their carbon fixation efficiency and is regulated by many environmental factors that impact photosynthesis, including carbon availability, light levels, and nutrient access. Efforts to connect the regulation of the CCM by these factors to functional effects on carbon assimilation rates have been complicated by the aqueous nature of cyanobacteria. Here, we describe the use of cyanobacteria in a semiwet state on glass fiber filtration discs—cyanobacterial discs—to establish dynamic carbon assimilation behavior using gas exchange analysis. In combination with quantitative PCR (qPCR) and transmission electron microscopy (TEM) analyses, we linked the regulation of CCM components to corresponding carbon assimilation behavior in the freshwater, filamentous cyanobacterium Fremyella diplosiphon. Inorganic carbon (C_i) levels, light quantity, and light quality have all been shown to influence carbon assimilation behavior in F. diplosiphon. Our results suggest a biphasic model of cyanobacterial carbon fixation. While behavior at low levels of CO₂ is driven mainly by the C_i uptake ability of the cyanobacterium, at higher CO₂ levels, carbon assimilation behavior is multifaceted and depends on C_i availability, carboxysome morphology, linear electron flow, and cell shape. Carbon response curves (CRCs) generated via gas exchange analysis enable rapid examination of CO₂ assimilation behavior in cyanobacteria and can be used for cells grown under distinct conditions to provide insight into how CO₂ assimilation correlates with the regulation of critical cellular functions, such as the environmental control of the CCM and downstream photosynthetic capacity.

中文翻译：

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将二氧化碳浓缩机制的动态响应与双叶藻的碳同化行为联系起来。

蓝藻使用二氧化碳 (CO ₂ ) 浓缩机制 (CCM) 来提高其碳固定效率，并受到许多影响光合作用的环境因素的调节，包括碳可用性、光照水平和养分获取。由于蓝藻的水性，将这些因素对 CCM 的调节与碳同化速率的功能影响联系起来的努力变得复杂化。在这里，我们描述了在玻璃纤维过滤盘（蓝藻盘）上使用半湿状态的蓝藻，通过气体交换分析建立动态碳同化行为。结合定量 PCR (qPCR) 和透射电子显微镜 (TEM) 分析，我们将 CCM 成分的调节与淡水丝状蓝藻Fremyella dilosiphon中相应的碳同化行为联系起来。无机碳 (C _i ) 水平、光量和光质量均已被证明会影响双倍管虫的碳同化行为。我们的结果提出了蓝藻固碳的双相模型。虽然低 CO ₂水平下的行为主要由蓝藻的C _i吸收能力驱动，但在较高 CO ₂水平下，碳同化行为是多方面的，并且取决于 C _i可用性、羧基形态、线性电子流和细胞形状。通过气体交换分析生成的碳响应曲线 (CRC) 能够快速检查蓝藻中的 CO ₂同化行为，并可用于在不同条件下生长的细胞，以深入了解 CO ₂同化与关键细胞功能调节的关系，例如CCM 和下游光合能力的环境控制。