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它来提供固定碳。在有氧环境中，RuBisCO努力有效地区分CO2和O2。为了补偿，许多光合生物发展了CO2浓缩机制（CCM）来增加RuBisCO活性位点周围的[CO2]。在蓝藻中，羧基体代表了这样一种CCM，其中存在两种独立的形式：α和β。这一古老的光合自养谱系已经成功地在世界范围内殖民栖息地，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两个最丰富的光合类群，主导着海洋生态系统。这些海洋微蓝细菌具有IA型RuBisCO和α-羧基体（所谓的α-蓝细菌）。蓝细菌辐射的其余部分被认为具有β-羧基体和IB型RuBisCO（β-蓝细菌），包括淡水单细胞和丝状水华形成分类群，包括世界各地实验室使用的模式生物，例如细长聚球藻和集胞藻。然而，最近我已经分离和测序了许多新的单细胞淡水微蓝细菌的基因组，这些微蓝细菌在遗传学上更接近于它们的海洋对应物，并且也具有IA型RuBisCO和α-羧基体。此外，在世界各地的淡水湖泊和水库中发现了高丰度的这些生物。因此，α-蓝藻主宰所有水生系统。CYANOUB寻求解决为什么会出现这种情况。我们假设，α-蓝藻占主导地位的大，时间稳定的水体，其特点是缓冲良好的pH值和碳酸盐化学相对缓慢的变化。CYANOUB对于准确预测生物圈对不断变化的CO2、pH值和碳酸盐化学的反应至关重要，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.