Genetic modification of sucrose levels in Anabaena sp.: towards the understanding of the role ofsucrose in cyanobacteria

CURATTI LEONARDO; SALERNO GRACIELA

Villa Carlos Paz, Argentina

Congreso; ###### Reunión Anual de la SAIBBM; 2001

Sucrose-phosphate synthase (SPS), sucrose-phosphate phosphatase (SPP), sucrose synthase (SuS) and invertase (Inv) control sucrose levels in plants and cyanobacteria. Sucrose is essential in plant life, being the major product of photosynthesis, with a central role in transport, growth, development, and stress tolerance. Much less is known about sucrose metabolism in cyanobacteria. In this work we have analyzed its role by genetic modification of the SuS levels in Anabaena sp. Two susA mutants (LC30, an insertional mutant, and LC60, a SusA overexpressing strain) were constructed. In LC30, both SuS activity and SusA polypeptide were not detected; conversely, in LC60, they were 10-fold increased. Sucrose levels were dramatically high in LC30, while they were not detected in LC60. The LC60 phenotype showed several pleiotrophic differences in comparison with LC30 and Anabaena sp. Its generation time was incremented in basal medium containing NO3- and its diazotrophic growth was severely affected. The vegetative cell/heterocyst size ratio, the accumulation of inclusion bodies and the trichome length were also modified. These results indicate that sucrose plays a relevant role in Anabaena sp. Basal metabolism. Importantly, the diazotrophic growth sensitivity of LC60 is, as far as we know, the most reliable evidence supporting a role of sucrose as a reductant carrier molecule from vegetative cells to heterocysts during Anabaena sp. Nitrogen fixation