A new appraisal on sucrose cleavage in cyanobacteria

Los Angeles

Workshop; 10th Cyanobacterial Molecular Biology Worshop; 2010

In cyanobacteria, sucrose synthesis through a similar two-step pathway has been described in both unicellular and filamentous nitrogen-fixing strains [1]. 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 [1,2]. SuS occurrence has been reported to be restricted to filamentous diazotrophic strains [1]. In the present work, by heterologous expression and biochemichal and immunological studies, we functionally characterized SuS encoding genes (sus) in three no nitrogen-fixing unicellular strains. Based on the presence of sus homologs in the most recently radiated cyanobacterial species, whose genomes have been fully sequenced (57 in total), and after phylogenetic analysis, we concluded that SuS may play a key role in phylamentous-nitrogen fixing strains. However, in unicellular strains, sus genes might have been acquired by horizontal gene transfer, and its physiological function has not been elucidated yet. This hypothesis is reinforced by the fact that sus gene is located in the middle of a sucrose metabolism gene cluster in the Microcystis aeruginosa genome. Supported by PICT 21227, PIP 2008, UNMdP and FIBA. [1] G.L.Salerno, L.Curatti. Trends Plant Scie 8, 63-69 (2003); [2] W. Vargas, A. Cumino, G.L.Salerno. Planta 216, 951-960 (2003).