(119f) Deciphering Cyanobacterial Phenotypes for Fast Photoautotrophic Growth

cyanobacterium characterized to date. Its genome was found to be 99.8% identical to

Synechococcus elongatus 7942, yet it grows twice as fast. Microbial physiological studies

mainly focus on genome/transcription/protein levels, but a cell's fluxes and

metabolome represent the actual function outputs across multiple levels. Current

genome-to-phenome mapping is still poorly performed for nonmodel organisms. Even

for species with identical genomes, cell phenotypes can be strikingly different. To

understand Synechococcus 2973's fast-growth phenotype, isotopically nonstationary

metabolic flux analysis (INST-MFA), biomass compositional analysis, gene knockouts,

and metabolite profiling were performed on both strains under various growth

conditions. The Synechococcus 2973 flux maps demonstrate strong Calvin cycle,

photorespiration, and pyruvate kinase activity, but minimal flux through malic enzyme

and oxidative pentose phosphate pathways. Moreover, central metabolite pool sizes

under optimal conditions were found to be lower, while under suboptimal light the cell

accumulates central metabolites. In addition, Synechococcus 2973 shows similar flux

ratios to Synechococcus 7942, but exhibited greater carbon assimilatory and

photorespiratory flux, less accumulation of glycogen, and potentially metabolite

channeling. Finally, Synechococcus 2973 has weak flux through a linear TCA pathway

and small pool sizes of acetyl-CoA/TCA intermediates under all growth conditions.

This study employed experimental dynamic flux analysis methodologies

to obtain new insights into optimal photoautotrophic metabolisms. The outcomes

indicate a highly effective metabolism in Synechococcus 2973 compared to other

model cyanobacteria. Metabolite pool sizes indicate energy metabolism, rather than

carbon fixation pathways, constrains fast cyanobacterial growth under our

experimental conditions. Together, the strain's many features, such as glycogen

accumulation, carbon assimilatory and metabolite channeling, result in increased

biomass growth and support a photosynthetic platform to produce valuable products

from its sugar phosphate pathways.