title: Catabolic function of compartmentalized alanine dehydrogenase in the heterocyst-forming cyanobacterium Anabaena sp. strain PCC 7120.
abstract: In the diazotrophic filaments of heterocyst-forming cyanobacteria, an exchange of metabolites takes place between vegetative cells and heterocysts that results in a net transfer of reduced carbon to the heterocysts and of fixed nitrogen to the vegetative cells. Open reading frame alr2355 of the genome of Anabaena sp. strain PCC 7120 is the ald gene encoding alanine dehydrogenase. A strain carrying a green fluorescent protein (GFP) fusion to the N terminus of Ald (Ald-N-GFP) showed that the ald gene is expressed in differentiating and mature heterocysts. Inactivation of ald resulted in a lack of alanine dehydrogenase activity, a substantially decreased nitrogenase activity, and a 50% reduction in the rate of diazotrophic growth. Whereas production of alanine was not affected in the ald mutant, in vivo labeling with [14C]alanine (in whole filaments and isolated heterocysts) or [14C]pyruvate (in whole filaments) showed that alanine catabolism was hampered. Thus, alanine catabolism in the heterocysts is needed for normal diazotrophic growth. Our results extend the significance of a previous work that suggested that alanine is transported from vegetative cells into heterocysts in the diazotrophic Anabaena filament.
authors.affiliation: Instituto de Bioquímica Vegetal y Fotosíntesis, Centro de Investigaciones Científicas Isla de la Cartuja, Américo Vespucio 49, E-41092, Seville, Spain.
authors.forename: Rafael
authors.initials: R
authors.lastname: Pernil
authors.forename: Antonia
authors.initials: A
authors.lastname: Herrero
authors.forename: Enrique
authors.initials: E
authors.lastname: Flores
mesh_terms: D000409:Alanine / Q000378:metabolism; D050788:Alanine Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D017033:Anabaena / Q000235:genetics / Q000378:metabolism*; D001426:Bacterial Proteins / Q000235:genetics / Q000378:metabolism*; D015964:Gene Expression Regulation, Bacterial; D018613:Microscopy, Confocal; D019289:Pyruvic Acid / Q000378:metabolism
chemical_list: D001426:Bacterial Proteins; D019289:Pyruvic Acid; D050788:Alanine Dehydrogenase; D000409:Alanine