Periplasmic α-carbonic anhydrase plays an essential role in Ralstonia eutropha CO2 metabolism

Background Carbonic anhydrase (CA) enzymes catalyze the interconversion of CO2 and bicarbonate. These enzymes play important roles in cellular metabolism such as CO2 transport, ion transport, and internal pH regulation. Understanding the roles of CAs in the chemolithotropic betaproteobacteria Ralstonia eutropha is important for the development of fermentation processes based on the bacterium’s capacity for carbon fixation using the CalvinBenson-Bassham cycle. Of the five classes of CA, the alpha-CA is the best-characterized thus far. The gene encoding a periplasmic alpha-CA (caa, H16 B2403) has been identified in the R. eutropha H16 genome, along with three others CA from different classes. In this study, we evaluated the importance of Caa in the metabolism of R. eutropha by examination of CA activity and growth in caa gene deletion, complementation, and overexpression strains. Localization of Caa in the cell was accessed by fluorescent microscopy.