Molecular and physiological analysis of the cyanobacterial CO2 concentrating mechanism

蓝藻是生活在世界海洋、湖泊和土壤中的一种非常小的微生物。就像“绿色”植物一样，它们从阳光中获取生长所需的能量，并将这些能量与二氧化碳(CO2)和水一起用来制造糖，作为它们的食物来源。这个过程被称为光合作用，也会产生氧气作为副产品。其他不能进行光合作用的生物以蓝藻为食物来源，从而间接从太阳获得能量。事实上，蓝藻和藻类是海洋和湖泊中制造的大多数“食物”的初级生产者，它们可能贡献了地球初级生产量的50%。我们实验室感兴趣的是了解控制光合作用效率的因素，从而影响初级生产力。影响光合作用的一个主要因素是二氧化碳转化为糖的有效性。我们已经发现，蓝藻有一种机制，允许它们在细胞内浓缩二氧化碳，比环境中的二氧化碳高出1000倍。这意味着光合作用将以高速率进行，从而增加产量。细胞内高浓度的二氧化碳也会抑制光呼吸，这会无意中浪费糖分，降低产量。我们已经发现，蓝藻中非常小的隔间，称为羧基体，对驱动光合作用的二氧化碳浓缩系统非常重要。我们正在使用重组DNA技术和其他复杂的程序来探索羧基体的结构和功能，以及它们如何帮助改善光合作用。我们还在确定控制二氧化碳浓缩系统表达的环境因素，以了解蓝藻细胞如何感知环境的变化并做出适当的反应。我们大多数重要的经济作物缺乏二氧化碳浓缩机制，因此由于光呼吸的浪费过程，它们的年产量损失了约30%。有朝一日，我们可能会利用我们新发现的关于二氧化碳浓缩系统的知识来提高农作物的产量，或者使用蓝藻来生产生物燃料。

Cyanobacteria are very small microorganism that live in the oceans, lakes and soil of the world. Like "green" plants they derive the energy needed to grow by harvesting the energy in sunlight and using this energy along with carbon dioxide (CO2) and water to make sugars, which serve as their food source. This process is called photosynthesis and also yields oxygen as a byproduct. Other organisms, which can not carry out photosynthesis, eat cyanobacteria as their food source and thereby gain energy from the sun indirectly. In fact, cyanobacteria and algae are the primary producers of most of the "food" manufactured in oceans and lakes and may contribute up to 50 % of the primary production of the earth. Our laboratory is interested in understanding the factors that control the efficiency of photosynthesis and therefore affect primary productivity. One major factor that affects photosynthesis is the availability of CO2 for conversion to sugars. We have discovered that the cyanobacteria have a mechanism which allows them to concentrate CO2 inside the cell up to1,000 times higher than in their environment. This means that photosynthesis will proceed at a high rate, increasing yield. The high concentration of CO2 inside the cells also suppresses photorespiration which inadvertently wastes sugars and reduces yield. We have found that very small compartments inside cyanobacteria, called carboxysomes, are quite important to the CO2 concentrating system that drives photosynthesis. We are using recombinant DNA technology and other sophisticated procedures to explore the structure and function of carboxysomes and how they help to improve photosynthesis. We are also determining the environmental factors that control the expression of the CO2-concentrating system in order to understand how cyanobacterial cells sense changes in their environment and respond appropriately. Most of our economically important crop plants lack a CO2 concentrating mechanism and thus lose about 30 % of their annual yield to the wasteful process of photorespiration. One day, it may be possible to use our new-found knowledge about the CO2 concentrating system to improve the yield of our crop plants or to use cyanobacteria to produce biofuels.