Carbonic Anhydrase in Anoxygenic Phototrophic Bacteria

— The genes encoding carbonic anhydrase (CA) were found in all anoxygenic purple bacteria. The genes of α- and β-CA were found in purple nonsulfur bacteria of the class Alphaproteobacteria: Rhodospirillum rubrum , Rhodospirillum fulvum , Rhodoblastus acidophilus , and Rhodopseudomonas palustris . The alphaproteobacteria Rhodomicrobium vannielii , Blastochloris viridis , Rhodobacter sphaeroides , Rhodobacter capsulatus , Rhodobacter veldkampii , Rhodovulum euryhalinum , and Rhodovulum sulfidophilum possessed only the β-CA genes. Both nonsulfur purple bacteria of the class Betaproteobacteria ( Rubrivivax gelatinosus ) and purple sulfur bacteria (class Gammaproteobacteria ) contained the α- and β-CA. No CA genes were found in green sulfur bacteria Chlorobaculum limnaeum and Chlorobaculum parvum , as well as in filamentous green nonsulfur bacteria Chloroflexus aurantiacus . However, the β-CA gene was revealed in Oscillochloris trichoides , which belonged to the latter taxonomic group. No γ-CA genes were detected in the genomes of the phototrophic bacteria studied in the present work. Although CA genes were present in all purple bacteria, the α- and β-CA activity was observed only in four species of purple nonsulfur Alphaproteobacteria : Rhodospirillum rubrum , Rhodopseudomonas palustris , Rhodoblastus acidophilus , and Rhodospirillum fulvum . These bacteria are able to synthesize CA under both photoautotrophic and photoheterotrophic conditions in the media with acetate, malate, or fructose. These bacteria (except for Rhodospirillum fulvum , which is unable to grow under aerobic conditions), also exhibit CA activity when grown under aerobic conditions in the dark.