Research Article Dispensabilities of Carbonic Anhydrase in Proteobacteria

Copyright © 2012 Kenji Ueda et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Carbonic anhydrase (CA) (E.C. 4.2.1.1) is a ubiquitous enzyme catalysing interconversion between CO2 and bicarbonate. The irregular distribution of the phylogenetically distinct classes of CA in procaryotic genome suggests its complex evolutionary history in procaryotes. Genetic evidence regarding the dispensability of CA under high-CO2 air in some model organisms indicates that CA-deficient microorganisms can persist in the natural environment by choosing high-CO2 niches. In this study, we studied the distribution of CA in the genome of Proteobacteria. While a large majority of the genome-sequenced Proteobacteria retained a CA gene(s), intracellular bacterial genera such as Buchnera and Rickettsia contained CA-defective strains. Comparison between CA-retaining and CA- deficient genomes showed the absence of whole coding sequence in some strains and the presence of frameshifted coding sequence in other strains. The evidence suggests that CA is inactivated and lost in some proteobacteria during the course of evolution based on its dispensability. Carbonic anhydrase (CA) (EC 4.2.1.1) is a ubiquitous en-zyme catalysing interconversion between CO2 and bicarbon-ate (HCO3 −) [1, 2]. CA is fundamental to various biologica