Dataset for "Heterologous expression in E. coli reveals the bicarbonate transporter BicA2 drives carbon uptake in marine Prochlorococcus spp."

The widespread oceanic cyanobacterial Prochlorococcus clade is a major contributor to global carbon fixation, yet mechanisms enabling this lineage to elevate intracellular inorganic carbon as a substrate for photosynthesis remain unresolved. Cyanobacterial CO2 concentrating mechanisms (CCMs) typically rely on membrane-bound bicarbonate (HCO3-) transporters SbtA1, SbtA2, BicA and BCT1, and CO2-to-HCO3- conversion uptake systems (CO2 pumps; NDH-I3 and NDH-I4), to elevate a cellular HCO3- pool for use by Rubisco-containing carboxysomes. Evidence suggests Prochlorococcus harbours carboxysomes with a low-CO2-specificity Rubisco, implying a functional CCM dependent on active HCO3- uptake. However, canonical CO2 pumps are absent, leaving distant HCO3- transporter homologues, BicA2 and SbtA2, as prime candidates for HCO3- transport in this group. Yet these have not been functionally characterised. Here we demonstrate that BicA2 from P. marinus CCMP1375 mediates Na+-dependent HCO3- uptake in E. coli, while BicA2 from P. marinus CCMP1986 is inactive in its native form but acquired transport function through a single amino acid substitution during adaptive laboratory evolution. These findings confirm BicA2 as a low-affinity, Na+-dependent bicarbonate transporter with variable flux, revealing a previously uncharacterized CCM component in Prochlorococcus. This mechanistic insight reshapes our understanding of carbon acquisition strategies in the most abundant photosynthetic organism on Earth and highlights evolutionary plasticity in transporter function with implications for global biogeochemical cycles.广泛分布于海洋的蓝细菌原绿球藻（Prochlorococcus）演化支是全球碳固定的主要贡献者，但该演化支提升细胞内无机碳水平以作为光合作用底物的具体机制仍未阐明。蓝细菌的二氧化碳浓缩机制（CO2 concentrating mechanisms, CCMs）通常依赖于膜结合型碳酸氢根（HCO3-）转运蛋白SbtA1、SbtA2、BicA与BCT1，以及CO2向HCO3-转化的摄取系统（CO2泵；NDH-I3与NDH-I4），以提升细胞内HCO3-池，供携带核酮糖-1,5-二磷酸羧化酶/加氧酶（Rubisco）的羧酶体（carboxysomes）使用。已有证据表明，原绿球藻拥有带有低CO2特异性Rubisco的羧酶体，暗示其功能性CCM依赖于主动HCO3-摄取。然而，该类群缺少典型的CO2泵，因此亲缘关系较远的HCO3-转运蛋白同源物BicA2与SbtA2成为该类群HCO3-转运的核心候选对象，但目前尚未对这些转运蛋白进行功能表征。本研究证实，来自海洋原绿球藻CCMP1375的BicA2可在大肠杆菌（E. coli）中介导钠依赖型HCO3-摄取；而来自海洋原绿球藻CCMP1986的BicA2在天然状态下无转运活性，但通过适应性实验室进化过程中的单个氨基酸替换即可获得转运功能。上述研究结果确认BicA2是一种可变通量的低亲和力钠依赖型碳酸氢根转运蛋白，揭示了原绿球藻中此前未被表征的CCM组分。这一机制层面的研究发现重塑了我们对地球上丰度最高的光合生物的碳获取策略的认知，并凸显了转运蛋白功能的进化可塑性，该发现对全球生物地球化学循环具有重要启示意义。