Acclimation to High CO Requires the Subunit of the RNA Polymerase in .

Inactivation of the nonessential ω-subunit of the RNA polymerase core in the ΔrpoZ strain of the model cyanobacterium sp. PCC 6803 leads to a unique high-CO-sensitive phenotype. Supplementing air in the growth chamber with 30 mL L (3%) CO accelerated the growth rate of the control strain (CS) 4-fold, whereas ΔrpoZ did not grow faster than under ambient air. The slow growth of ΔrpoZ during the first days in high CO was due to the inability of the mutant cells to adjust photosynthesis to high CO The light-saturated photosynthetic activity of ΔrpoZ in high CO was only half of that measured in CS, Rubisco content was one-third lower, and cells of ΔrpoZ were not able to increase light-harvesting phycobilisome antenna like CS upon high-CO treatment. In addition, altered structural and functional organization of photosystem I and photosystem II were detected in the ΔrpoZ strain compared with CS when cells were grown in high CO but not in ambient air. Moreover, respiration of ΔrpoZ did not acclimate to high CO Unlike the photosynthetic complexes, the RNA polymerase complex and ribosomes were produced in high CO similarly as in CS Our results indicate that the deletion of the ω-subunit specifically affects photosynthesis and respiration, but transcription and translation remain active. Thus, the specific effect of the ω-subunit on photosynthesis but not on all household processes suggests that the ω-subunit might have a regulatory function in cyanobacteria.