Sucrose catabolism pathways in cyanobacteria

SALERNO, G; KOLMAN, MA; PEREZ-CENCI, M; NISHI, CN

Mar del Plata

Congreso; X Congreso de Microbiologia General; 2014

Sociedad Argentina de Microbiologia General

The increasing number of complete sequenced genomes of oxygenic photosynthetic organisms let us to continue our study on sucrose metabolism proteins. Sucrose synthesis through a similar two-step pathway has been described in both unicellular and filamentous nitrogen-fixing strains. In addition, sucrose catabolism can take place through its hydrolysis by alkaline/neutral invertases or its cleavage by sucrose synthase (SuS, UDP?glucose:D-fructose 2-a-D-glucosyltransferase, EC 2.4.1.13), supplying sugar nucleotides, precursors in the formation of structural and storage polysaccharides. Recently, a new hydrolysis pathway has been described involving an amylosucrase (AMS) that belongs to glycoside hydrolase (GH) family 13 that not only to hydrolyze Suc to monosaccharides supplying carbon and energy, but also to synthesize amylose-like polymers. Based on the presence of sus homologs in the most recently radiated cyanobacterial species, whose genomes have been fully sequenced (198 in total), and after phylogenetic analysis, we concluded that SuS may play a key role in heterocyst-forming strains, while in unicellular strains is likely to be dispensable in some cases or related to environmental adverse conditions as has been demonstrated in M. aeruginosa. The presence of inv homologs is found in the 65% of all cyanobacteria and its early origin is reflected by its presence at the base of the radiation. Additionally, in the 60% of cases are nitrogen-fixing cyanobacteria and, as occurs with SuS, InvA/N are ubiquitous in all heterocyst-forming cyanobacteria, where plays a crucial function in the heterotrophic metabolism in the heterocysts. There is little information about the AMS, homology searches show its presence in 2 filamentous and in 8 unicellular cyanobacteria, where this was the only catabolic pathway. The phylogenetic analysis showed that this enzyme has a bacterial origin and would have been acquired in separate events.Phylogenetic analysis of the different paths of cleavage / hydrolysis of sucrose in cyanobacteria show that the origin of the InvA/N was early in the evolution, while the appearance of SuS was posterior and fundamental in the development of more evolved morphological forms, this is reflected in the fact that their presence shows a pattern of patches in unicellular cyanobacteria, while filamentous heterocyst- and akinete- forming as well as in branched strains, is always present.