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Titel (primär) Heterologous lactate synthesis in Synechocystis sp. strain PCC 6803 causes a growth condition-dependent carbon sink effect
Autor Grund, M.; Jakob, T.; Toepel, J.; Schmid, A.; Wilhelm, C.; Bühler, B.
Journal / Serie Applied and Environmental Microbiology
Erscheinungsjahr 2022
Department SOMA
Band/Volume 88
Heft 8
Seite von e00063-22
Sprache englisch
Topic T7 Bioeconomy
Keywords carbon fixation; cyanobacteria; electron flow; lactate production; photosynthetic efficiency; quantitative physiology; source sink balance
Abstract Cyanobacteria are considered promising hosts for product synthesis directly from CO2 via photosynthetic carbon assimilation. The introduction of heterologous carbon sinks in terms of product synthesis has been reported to induce the so-called “carbon sink effect,” described as the release of unused photosynthetic capacity by the introduction of additional carbon. This effect is thought to arise from a limitation of carbon metabolism that represents a bottleneck in carbon and electron flow, thus enforcing a downregulation of photosynthetic efficiency. It is not known so far how the cellular source/sink balance under different growth conditions influences the extent of the carbon sink effect and in turn product formation from CO2, constituting a heterologous carbon sink. We compared the Synechocystis sp. strain PCC 6803 wild type (WT) with an engineered lactate-producing strain (SAA023) in defined metabolic states. Unexpectedly, high-light conditions combined with carbon limitation enabled additional carbon assimilation for lactate production without affecting biomass formation. Thus, a strong carbon sink effect only was observed under carbon and thus sink limitation, but not under high-sink conditions. We show that the carbon sink effect was accompanied by an increased rate of alternative electron flow (AEF). Thus, AEF plays a crucial role in the equilibration of source/sink imbalances, presumably via ATP/NADPH balancing. This study emphasizes that the evaluation of the biotechnological potential of cyanobacteria profits from cultivation approaches enabling the establishment of defined metabolic states and respective quantitative analytics. Factors stimulating photosynthesis and carbon fixation are discussed.
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Grund, M., Jakob, T., Toepel, J., Schmid, A., Wilhelm, C., Bühler, B. (2022):
Heterologous lactate synthesis in Synechocystis sp. strain PCC 6803 causes a growth condition-dependent carbon sink effect
Appl. Environ. Microb. 88 (8), e00063-22