CARBON-CONCENTRATING MECHANISMS: PHYLOGENETIC STUDIES OF CARBOXYSOME PROTEINS IN CYANOBACTERIA

MARTIN, MV; CAINZOS, M; KOLMAN, MA; SALERNO, G

Mar del Plata

Congreso; X Congreso de Microbiologia General; 2014

SAMIGE

Cyanobacteria live in a diverse range of ecological habitats, including both freshwater and marine ecosystems and play a key role in the biogeochemical carbon and nitrogen cycle. The ability of this diverse group of photoautotrophs to assimilate carbon dioxide (CO2) from the environment comes from the Carbon Concentrating Mechanisms (CCM). The CCM comprises inorganic carbon (Ci, as CO2 and HCO3-) transporters for Ci uptake and protein microbodies called carboxysomes for CO2 concentration and fixation by Rubisco. There are two main phylogenetic groups within the cyanobacteria based on Rubisco and carboxysome phylogenies. Alpha-cyanobacteria have alpha-carboxysomes with form-IA Rubisco, whereas beta-cyanobacteria have beta-carboxysomes with form-IB Rubisco. The two types of carboxysomes are morphologically similar but differ in that shell proteins are encoded by the cso (csoS123AB) operon, in the case of alpha-carboxysomes, or by ccm (ccmKLMN) operon, in the case of beta-carboxysomes. HCO3- dehydration is catalyzed by carbonic anhydrase (CA) specifically localized in the center of the carboxysomes. Its function results in the accumulation of CO2 in high concentrations in the vicinity of Rubisco to promote Ci fixation. Recently, the number of sequenced cyanobacterial genomes has been duplicated and more than 190 genomes are available. Thus, new phylogenetic and genetic studies are needed. In this work, phylogenetic analyses indicate that beta-cyanobacteria evolved first than alpha-cyanobacteria. Beta-cyanobacteria are widely distributed and occupy a more diverse range of habitats than alpha-cyanobacteria, including freshwater, estuarine, and hot springs. Furthermore, alpha-cyanobacteria, which inhabit in marine environments, have evolutionary relationship to the Proteobacteria. Alpha-cyanobacteria include only marine genera Prochlorococcus and Synechococcus. Besides, our genetic analyses, summarized the genetic diversity in the presence/absence of the CCM genes of the sequenced genomes. Most beta-cyanobacteria have beta-CAs inside its carboxysomes, but those that live in hot springs have a gamma-CA, potentially active, because they have the appropriate amino acids for a correct structure and a functional enzyme. Alpha cyanobacteria have only epsilon-CAs in their carboxysomes. Our results are the first step to a more comprehensive study of these proteins to shed some light on the evolution and function of cyanobacterial carboxysomes.