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Electron partitioning in soluble organic products by wild-type and modified Synechocystis sp. PCC 6803

Nguyen, Binh T., Rittmann, Bruce E.
Biomass and bioenergy 2016 v.90 pp. 237-242
Synechocystis, biomass, carbon, chemical oxygen demand, dodecanoic acid, electrons, embodied energy, light intensity, photosynthesis
The partitioning of electrons photosynthetically fixed in carbon by the cyanobacterium Synechocystis sp. PCC 6803 was evaluated for up to 24-day batch cultures continuously exposed to incident light intensity (LI) from 111 to 598 μEm−2 s−1. The fate of fixed electrons was assayed by Chemical Oxygen Demand (COD) in biomass, generic soluble microbial products (SMP), and excreted laurate (for a modified strain). Because SMP is not a valuable product, light energy embedded in SMP is wasted. Normalized to the total COD (TCOD), wild-type Synechocystis partitioned 75–84% of its TCOD in particulate biomass and 16–25% in generic SMP. A strain modified to excrete lauric acid partitioned 6.6%–10% of its TCOD in laurate, 21%–30% in generic SMP, and 64%–69% in particulate biomass. The greatest electron partitioning in SMP occurred with the highest LI tested, which suggests that moderating the LI in the photobioreactor is a promising mean to accentuate the production of valuable forms of photosynthetically fixed electrons.