Dark respiration modulates photosynthetic carbon yield in cyanobacteria

Abstract

Cyanobacteria contribute to roughly a quarter of global net carbon fixation. During diel light/dark growth, dark respiration significantly lowers the overall photosynthetic carbon yield in cyanobacteria and other phototrophs. Currently, it is unclear how photosynthetic organisms allocate carbon resources at night for optimal dark survival. Here we show in the cyanobacterium Synechococcus elongatus PCC 7942 that phosphoketolase and 2-keto-3-deoxy-6-phosphogluconate (KDPG) aldolase are orchestrated in an integrative respiratory network in the dark to best allocate carbon resource for amino acid synthesis and preparation for photosynthesis reinitiation upon photoinduction. We further show that the Entner-Doudoroff (ED) pathway is incomplete in S. elongatus with the KDPG aldolase participating in dark respiration through an alternative decarboxylation activity. Optimization of dark respiration thus represents a unique strategy to enhance photosynthetic carbon yield in cyanobacteria and other photosynthetic organisms.