Carbon Availability Affects Diurnally Controlled Processes and Cell Morphology of Cyanothece 51142

Cyanobacteria are oxygenic photoautotrophs notable for their ability to utilize atmospheric CO 2 as the major source of carbon. The prospect of using cyanobacteria to convert solar energy and high concentrations of CO 2 efficiently into biomass and renewable energy sources has sparked substantial interest in using flue gas from coal-burning power plants as a source of inorganic carbon. However, in order to guide further advances in this area, a better understanding of the metabolic changes that occur under conditions of high CO 2 is needed. To determine the effect of high CO 2 on cell physiology and growth, we analyzed the global transcriptional changes in the unicellular diazotrophic cyanobacterium Cyanothece 51142 grown in 8% CO 2 -enriched air. We found a concerted response of genes related to photosynthesis, carbon metabolism, respiration, nitrogen fixation, ribosome biosynthesis, and the synthesis of nucleotides and structural cell wall polysaccharides. The overall response to 8% CO 2 in Cyanothece 51142 involves different strategies, to compensate for the high C/N ratio during both phases of the diurnal cycle. Our analyses show that high CO 2 conditions trigger the production of carbon-rich compounds and stimulate processes such as respiration and nitrogen fixation. In addition, we observed that high levels of CO 2 affect fundamental cellular processes such as cell growth and dramatically alter the intracellular morphology. This study provides novel insights on how diurnal and developmental rhythms are integrated to facilitate adaptation to high CO 2 in Cyanothece 51142.