Molecular and physiological analysis of the cyanobacterial CO2 concentrating mechanism

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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.