The Freshwater Cyanobacterium Synechococcus elongatus PCC 7942 Does Not Require an Active External Carbonic Anhydrase.

Under standard laboratory conditions, Synechococcus elongatus PCC 7942 lacks EcaA Syn , a periplasmic carbonic anhydrase (CA). In this study, a S. elongatus transformant was created that expressed the homologous EcaA Cya from Cyanothece sp. ATCC 51142. This additional external CA had no discernible effect on the adaptive responses and physiology of cells exposed to changes similar to those found in S. elongatus natural habitats, such as fluctuating CO 2 and HCO 3 - concentrations and ratios, oxidative or light stress, and high CO 2 . The transformant had a disadvantage over wild-type cells under certain conditions (Na + depletion, a reduction in CO 2 ). S. elongatus cells lacked their own EcaA Syn in all experimental conditions. The results suggest the presence in S. elongatus of mechanisms that limit the appearance of EcaA Syn in the periplasm. For the first time, we offer data on the expression pattern of CCM-associated genes during S. elongatus adaptation to CO 2 replacement with HCO 3 - , as well as cell transfer to high CO 2 levels (up to 100%). An increase in CO 2 concentration coincides with the suppression of the NDH-1 4 system, which was previously thought to function constitutively.