Glycogen Synthesis and Metabolite Overflow Contribute to Energy Balancing in Cyanobacteria

• Published in: Cell reports (Cambridge) 2018-04, Vol.23 (3), p.667-672
• Main Authors: Cano, Melissa, Holland, Steven C., Artier, Juliana, Burnap, Rob L., Ghirardi, Maria, Morgan, John A., Yu, Jianping
• Format: Article
• Language: English
• Subjects: 09 BIOMASS FUELS; cyanobacteria; energy charge; glycogen; overflow metabolism; photosynthesis; synechocystis
• ISSN: 2211-1247; 2211-1247
• DOI: 10.1016/j.celrep.2018.03.083

Understanding how living cells manage high-energy metabolites such as ATP and NADPH is essential for understanding energy transformations in the biosphere. Using light as the energy input, we find that energy charge (ratio of ATP over ADP+ATP) in the cyanobacterium Synechocystis sp. PCC 6803 varies in different growth stages, with a peak upon entry into the rapid growth phase, as well as a positive correlation with light intensity. In contrast, a mutant that can no longer synthesize the main carbon storage compound glycogen showed higher energy charge. The overflow of organic acids in this mutant under nitrogen depletion could also be triggered under high light in nitrogen-replete conditions, with an energy input level dependency. These findings suggest that energy charge in cyanobacteria is tightly linked to growth and carbon partition and that energy management is of key significance for their application as photosynthetic carbon dioxide-assimilating cell factories. [Display omitted] •ATP levels in a cyanobacterium vary according to growth phase and environment•A glycogen-deficient strain shows difference in ATP levels and photosynthesis•Glycogen synthesis/degradation is an important cellular energy buffer•Metabolite overflow is an alternative energy dissipation mechanism Cano et al. find that ATP levels in a cyanobacterium are dynamic in growth phases and respond to intracellular and environmental conditions. A glycogen mutant excretes organic acids and adjusts photosynthesis as alternative strategies to maintain energy homeostasis.