Effect of light fluctuations on photosynthesis and metabolic flux in Synechocystis sp. PCC 6803

Abstract

In nature, photosynthetic organisms are exposed to fluctuating light, and their physiological systems must adapt to this fluctuation. To maintain homeostasis, these organisms have a light fluctuation photoprotective mechanism, which functions in both photosystems and metabolism. Although the photoprotective mechanisms functioning in the photosystem have been studied, it is unclear how metabolism responds to light fluctuations within a few seconds. In the present study, we investigated the metabolic response of Synechocystis sp. PCC 6803 to light fluctuations using 13C‐metabolic flux analysis. The light intensity and duty ratio were adjusted such that the total number of photons or the light intensity during the low‐light phase was equal. Light fluctuations affected cell growth and photosynthetic activity under the experimental conditions. However, metabolic flux distributions and cofactor production rates were not affected by the light fluctuations. Furthermore, the estimated ATP and NADPH production rates in the photosystems suggest that NADPH‐consuming electron dissipation occurs under fluctuating light conditions. Although we focused on the water–water cycle as the electron dissipation path, no growth effect was observed in an flv3‐disrupted strain under fluctuating light, suggesting that another path contributes to electron dissipation under these conditions.

Model validation and selection in metabolic flux analysis and flux balance analysis

“…Since its development as a validation method in 13C-MFA, 26 the χ 2 -test has been widely used and has been useful in the validation of 13C-MFA metabolic models inferred from genome annotations. [86][87][88][89][90][91][92] However, as described in Ref. 93,27 the use of the χ 2 -test can be problematic in 13C-MFA for several reasons.…”

“…The χ 2 ‐test of goodness‐of‐fit, which is built into commonly used 13C‐MFA software, 83–85 is then used to test whether the SSR falls within the 95% confidence interval expected for the defined number of degrees of freedom (DOF). Since its development as a validation method in 13C‐MFA, 26 the χ 2 ‐test has been widely used and has been useful in the validation of 13C‐MFA metabolic models inferred from genome annotations 86–92 …”

Methanogenesis in the presence of oxygenic photosynthetic bacteria may contribute to global methane cycle

“…PCC6803 is a model oxygenic photosynthetic bacterium that can perform solar energy conversion of water and CO 2 to carbohydrates and oxygen. In the absence of light, the produced carbohydrates are metabolized to generate CO 2 and ATP through a respiratory system, creating an anoxic microenvironment suitable for microbial methanogenesis 18 . Meanwhile, M. b as a model methanogen was chosen owing to its widespread environmental presence with physiological and metabolic diversity 19 .…”