To investigate the carbon metabolism and energy conversion efficiency of the cyanobacterium Synechococcus sp. PCC 7942 under mixotrophic conditions, we studied its growth characteristics in mixotrophic cultures with glucose and with acetate, respectively, and further discussed the carbon metabolism and energy utilization based on metabolic flux analysis. Results showed that both glucose and acetate could enhance the growth of Synechococcus sp. PCC 7942. The metabolic flux through the glycolytic pathway, tricarboxylic acid cycle, and mitochondrial oxidative phosphorylation was affected by the two organic substrates. Additionally, the cellular composition was also modulated by glucose and acetate. Under mixotrophic conditions, glucose exerts more significant impact on the diminishment of photochemical efficiency. Although the contribution of light energy was smaller, the cell yields based on total energy in mixotrophic cultures were higher compared with that of photoautotrophic one. On the basis of chlorophyll fluorescence analysis, the actual energy conversion efficiencies based on ATP synthesis in the photoautotrophic, glucose-mixotrophic, and acetatemixotrophic cultures were evaluated to be 4.59%, 5.86%, and 6.60%, respectively. Keywords Synechococcus sp. PCC 7942 . Mixotrophic cultivation . Carbon metabolism . Energy conversion . Metabolic flux analysis . Chlorophyll fluorescence analysis Nomenclature a ij Stoichiometric coefficient of metabolite i in the jth reaction (−) A m×nMatrix of stoichiometric coefficient (−) A 0 Side area of flask receiving incident light (m 2 ) E abLight energy absorbed by the biomass unit (kJ g −1 h −1 ) E P Actual light energy for photosynthesis (kJ g −1 h −1 ) E C Chemical energy received from organic carbon resources (kJ g −1 h −1 ) E C,ACE Chemical energy originated from acetate (kJ g −1 h −1 ) E C,GLC Chemical energy originated from glucoseThe total absorbed energy (kJ g −1 h −1 ) I 0 Incident light intensity (μmol m− 2 s −1 ) K a Effective absorption coefficient of light (m −1 ) rVector of m-dimensional metabolite accumulation rate (mmol g −1 h −1 ) r ATP Relative rate of ATP synthesized (mmol g −1 h −1 ) r ACE Relative rate of acetate consumption (mmol g −1 h −1 ) r ex Subvector of extracellular metabolite accumulation rate (mmol g −1 h −1 )Relative rate of glucose consumption (mmol g −1 h −1 ) r i Accumulation rate of metabolite i (mmol g −1 h −1 ) r in Subvector of intracellular metabolite accumulation rate (mmol gof cell mass based on ATP generation (g mol-ATP −1 ) Y E Cell yield based on total light energy (g kJ −1 ) ΔG o ACE Free energy change of acetate complete oxidation (kJ mol −1 ) ΔG o ATP Free energy change of ATP hydrolysis (kJ mol −1 ) ΔG o GLC Free energy change of glucose complete oxidation (kJ mol −1 ) μ Specific growth rate (h −1 ) 8 Vector of measurement noise variancecovariance (−) Φ PSII The efficiency of photosystem II photochemistry (−) Ψ ATP The efficiency of energy conversion on ATP synthesis (%)

No abstract

No abstract