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

Under standard laboratory conditions, PCC 7942 lacks EcaA, a periplasmic carbonic anhydrase (CA). In this study, a transformant was created that expressed the homologous EcaA from 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 natural habitats, such as fluctuating CO and HCO concentrations and ratios, oxidative or light stress, and high CO. The transformant had a disadvantage over wild-type cells under certain conditions (Na depletion, a reduction in CO). cells lacked their own EcaA in all experimental conditions. The results suggest the presence in of mechanisms that limit the appearance of EcaA in the periplasm. For the first time, we offer data on the expression pattern of CCM-associated genes during adaptation to CO replacement with HCO, as well as cell transfer to high CO levels (up to 100%). An increase in CO concentration coincides with the suppression of the NDH-1 system, which was previously thought to function constitutively.