Sucrose catabolism in filamentous and unicellular cyanobacteria under stress conditions.

KOLMAN, MA; NISHI, CN; SALERNO, G

Puerto Madryn, Chubut

Congreso; XLVI Reunion Anual Sociedad Argentina de la Investigacion Bioquimica y Biologia Molecular.; 2010

In cyanobacteria Suc is synthesized through a two-step pathway involving Suc-phosphate synthase and Suc-phosphate phosphatase and degraded by Suc Synthase (SuS) or Alkaline-Neutral Invertases (A/N-Inv). Suc cleavage by SuS had only been reported in filamentous heterocyst-forming cyanobacteria. Microcystis aeruginosa is a unicellular non-N fixing strain, well-known as one 2 of the most common bloom-forming strain in fresh water environments. By sequence analysis we retrieved an open reading frame homologous to SuS encoding gene in the M. aeruginosa PCC7806 genome. The sequence was cloned and functionally characterized by expression in E. coli cells. In addition, the SuS activity was measured in cell free extracts. The expression of SuS and A/N-Invs was also studied in Nostoc sp. PCC7120, a filamentous strain and in M. aeruginosa. Cultures of both cyanobacteria were subjected to different conditions of light, nitrogen and salt stress. Expression analysis showed that while the response to salt stress was similar in both strains, a different expression pattern was obtained for SuS and A/N-Inv encoding genes under dark and light conditions. Also SuS and A-N/Inv expression was activated in diazotrophic growth. Our results indicate a distinct role for the Suc catabolism proteins in unicellular and filamentous nitrogen fixing strains.