Why do alpha-cyanobacteria with form 1A RuBisCO dominate aquatic habitats worldwide? (CYANORUB)

RuBisCO是地球上最丰富的酶之一。几乎所有的食物网都依赖于它来提供固定碳。在有氧环境中，RuBisCO很难有效地区分CO2和O2。作为补偿，许多光合生物已经发展出二氧化碳浓缩机制（CCMs）来增加RuBisCO活性位点周围的[CO2]。在蓝藻中，羧酸体代表一种这样的CCM，其中存在两种独立的形式：α和β。这个古老的光自养谱系已经成功地殖民了世界各地的栖息地，是具有重要生态意义的初级生产者。其中，原绿球藻属和聚球藻属的细胞是地球上最丰富的两个光合类群，在海洋生态系统中占主导地位。这些海洋蓝藻菌具有IA RuBisCO和α -羧酸体（所谓的α -蓝藻菌）。蓝藻辐射的剩余部分被认为具有β -羧酸体和一种形式IB RuBisCO （β -蓝藻），包括淡水单细胞和丝状开花形成的分类群，包括世界各地实验室中使用的模式生物，如长聚球菌和聚囊藻。然而，最近我已经分离并测序了许多新的单细胞淡水picocyanobacteria的基因组，它们在系统发育上更接近于它们的海洋同类，并且也具有IA RuBisCO和α -羧酸体的形式。此外，这些生物在世界各地的淡水湖和水库中被检测到大量存在。因此，蓝藻在所有水生系统中占主导地位。CYANORUB试图解决为什么会出现这种情况。我们假设α蓝藻主导了大的、暂时稳定的水团，其特征是ph值缓冲良好，碳酸盐化学变化相对缓慢。CYANORUB对于准确预测生物圈对二氧化碳、pH值和碳酸盐化学变化的反应至关重要，并具有旨在改善植物生长的生物技术应用。

RuBisCO is one of the most abundant enzymes on Earth. Virtually all food webs depend on it to supply fixed carbon. In aerobicenvironments, RuBisCO struggles to distinguish efficiently between CO2 and O2. To compensate, many photosynthetic organismshave developed CO2-concentrating mechanisms (CCMs) to increase the [CO2] around the RuBisCO active site. In cyanobacteria,carboxysomes represent one such CCM, of which two independent forms exist: alpha and beta. This ancient photoautotrophiclineage has succeeded in colonizing habitats worldwide, being primary producers of great ecological importance. Amongst them,cells of the genera Prochlorococcus and Synechococcus, the two most abundant photosynthetic taxa on Earth, dominate oceanicecosystems. These marine picocyanobacteria possess a form IA RuBisCO and alpha-carboxysomes (so-called alpha-cyanobacteria).The remainder of the cyanobacterial radiation was thought to possess beta-carboxysomes and a form IB RuBisCO (beta-cyanobacteria), including freshwater unicellular and filamentous bloom-forming taxa comprising model organisms used inlaboratories worldwide e.g. Synechococcus elongatus and Synechocystis. However, recently I have isolated and sequenced thegenomes of many new unicellular freshwater picocyanobacteria that are phylogenetically much closer to their marine counterpartsand which also possess a form IA RuBisCO and alpha-carboxysomes. Moreover, these organisms have been detected in highabundance in freshwater lakes and reservoirs worldwide. Thus, alpha-cyanobacteria dominate all aquatic systems. CYANORUB seeksto address why this is the case. We hypothesize that alpha-cyanobacteria dominate large, temporally stable water masses,characterized by well-buffered pHs and relatively slow changes in carbonate chemistry. CYANORUB will be crucial for accuratelypredicting the biosphere's response to changing CO2, pH and carbonate chemistry and has biotechnological applications aimed atimproving plant growth.