Abstract
Cyanobacteria are oxygenic photoautotrophs notable for their ability to utilize atmospheric CO2 as the major source of carbon. The prospect of using cyanobacteria to convert solar energy and high concentrations of CO2 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 CO2 is needed. To determine the effect of high CO2 on cell physiology and growth, we analyzed the global transcriptional changes in the unicellular diazotrophic cyanobacterium Cyanothece 51142 grown in 8% CO2-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% CO2 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 CO2 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 CO2 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 CO2 in Cyanothece 51142.
Highlights
The significant increase in global energy consumption together with current and prospective economic growth is linked to severe concerns about rising CO2 emissions
Nitrogen fixing cultures of Cyanothece 51142 aerated with ambient and 8% CO2 grow at similar but significantly lower rates as compared to 1% CO2 (Figure 1). This result suggests that high CO2 conditions generate a nutritional and/or energetic imbalance that outweighs the beneficial effect of elevated CO2 on the growth rate
Almost all genes associated with photosynthesis exhibit reduced transcript levels whereas genes related to respiration are up-regulated in 8% CO2 conditions (Table S2)
Summary
The significant increase in global energy consumption together with current and prospective economic growth is linked to severe concerns about rising CO2 emissions. CO2 is the primary source of all organic carbon, and life on earth depends on the assimilation of CO2. Oxygenic photoautotrophic organisms such as cyanobacteria efficiently convert light into chemical energy using atmospheric CO2 and electrons from H2O while splitting off O2, and contribute significantly to the global carbon cycle. Many cyanobacterial strains thrive when provided with higher levels of CO2 because the rate limiting enzyme ribulose bisphosphate carboxylase-oxygenase (Rubisco) has a low affinity for CO2 [1]. The effects of CO2 on physiology and morphology in cyanobacteria have been primarily used to understand the mechanisms of carbon concentration under CO2 limiting conditions [2,3,4,5]
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