A comprehensive network structure for the autotrophic growth of Arthrospira platensis is proposed. The metabolic network was built up with 121 reactions and 134 metabolites including biomass synthesis, production of a growth-associated exopolysaccharide, and energy aspects. The model supports the existence of a metabolic shunt of PEP to pyruvate through PEP carboxylase, NAD(+) dependent malate dehydrogenase and malic enzyme to convert NADH,H+ into NADPH,H+. A limit in Arthrospira growth metabolism due to NADH,H+ balancing is evidenced, explaining why the maximal light-dependent mass yield of the growth-associated exopolysaccharide was 0.51 kg EPS kg(-1) biomass, consistent with experimental results. (C) 2003 Wiley Periodicals, Inc.