Differential roles of alkaline/neutral invertases in Nostoc sp. PCC 7120: Inv-B isoform is essential for diazotrophic growth

The presence of two alkaline/neutral invertases (Inv-A and Inv-B) in the filaments of Nostoc (also named Anabaena) sp. strain PCC 7120 and the involvement of sucrose metabolism in nitrogen fixation led us to investigate the physiological function of those isoforms in cells growing under different nitrogen sources. The highest expression level of each encoding gene was obtained in the presence of ammonium. These results were paralleled by polypeptide and enzyme activity level. In cells of N2-fixing filaments, localization of gene expression and subcellular enzyme activity assays demonstrated that invA gene (alr1521) expresses only in vegetative cells, whereas for invB (alr0819), expression is detected in both vegetative cells and heterocysts. In contrast to invA, when invB was knocked out, the filaments were unable to grow on diazotrophic conditions and the accumulation of sucrose and glycogen was altered. Our results demonstrate an essential role for Inv-B for diazotrophic growth and that Inv-B plays a key role in the coordination of sucrose and glycogen metabolism. We can also suggest that invB is likely to integrate the repertoire of genes regulated by a cyanobacterial transcription factor (NtcA) that plays a central role in global nitrogen control.Fil: Vargas, Walter Alberto. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación para Investigaciones Biológicas Aplicadas; Argentina. Universidad de Salamanca; España. Fundación para Investigaciones Biológicas Aplicadas; ArgentinaFil: Nishi, Carolina Nancy. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación para Investigaciones Biológicas Aplicadas; ArgentinaFil: Giarrocco, Laura Estela. Fundación para Investigaciones Biológicas Aplicadas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Salerno, Graciela Lidia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fundación para Investigaciones Biológicas Aplicadas; Argentin