Anabaena sp. PCC 7120 is a nitrogen-fixing filamentous cyanobacterium.
Under nitrogen limiting conditions, a fraction of the vegetative cells in each
filament terminally differentiate to non-growing heterocysts. Heterocysts are metabolically and s
tructurally specialized to enable O2 -sensitive nitrogen fixation. The functionality of the filament
, as an association of vegetative cells and heterocysts, is postulated to depend on me
tabolic exchange of electrons, carbon and fixed nitrogen. In the present work, we compile and
evaluate a comprehensive curated stoichiometric model of this two-cell system, with the
objective function based on the growth of the filament under diazotrophic conditions. The predi
cted growth rate under nitrogen replete and deplete conditions, as well as the effect
of external carbon and nitrogen sources, was thereafter verified. Furthermore, the model was utilized to comprehensively evaluate the optimality of putative metabolic exchange reaction
s between heterocysts and vegetative cells. The model suggested that optimal growth requi
res at least four exchange metabolites. Several combinations of exchange metabolites resul
ted in predicted growth rates that are higher than growth rates achieved by only considering
exchange of metabolites previously suggested in the literature. The curated model of the metabolic network of Anabaena sp. PCC 7120 enhances our ability to understand the metabolic
organization of multi-cellular cyanobacteria and provides a platform for further study and engineering of their metabolism