Characterization of Light-Enhanced Respiration in Cyanobacteria

Abstract

In eukaryotic algae, respiratory O2 uptake is enhanced after illumination, which is called light-enhanced respiration (LER). It is likely stimulated by an increase in respiratory substrates produced during photosynthetic CO2 assimilation and function in keeping the metabolic and redox homeostasis in the light in eukaryotic cells, based on the interactions among the cytosol, chloroplasts, and mitochondria. Here, we first characterize LER in photosynthetic prokaryote cyanobacteria, in which respiration and photosynthesis share their metabolisms and electron transport chains in one cell. From the physiological analysis, the cyanobacterium Synechocystis sp. PCC 6803 performs LER, similar to eukaryotic algae, which shows a capacity comparable to the net photosynthetic O2 evolution rate. Although the respiratory and photosynthetic electron transports share the interchain, LER was uncoupled from photosynthetic electron transport. Mutant analyses demonstrated that LER is motivated by the substrates directly provided by photosynthetic CO2 assimilation, but not by glycogen. Further, the light-dependent activation of LER was observed even with exogenously added glucose, implying a regulatory mechanism for LER in addition to the substrate amounts. Finally, we discuss the physiological significance of the large capacity of LER in cyanobacteria and eukaryotic algae compared to those in plants that normally show less LER.

Heterologous Lactate Synthesis in Synechocystis sp. Strain PCC 6803 Causes a Growth Condition-Dependent Carbon Sink Effect

“…This ensured that the conditions in the reactor and during the assay were as comparable as possible. O 2 evolution rates were determined for all light intensities and the respective respiration rates in a following dark phase (see also reference 60 ). The gross O 2 formation rate was calculated by correcting the measured O 2 evolution rate for the corresponding respiration rate.…”

Novel concepts and engineering strategies for heterologous expression of efficient hydrogenases in photosynthetic microorganisms

“…However, to our knowledge there are no reports about their implementation in any photosynthetic microorganism. In addition, respiration in photosynthetic organisms plays a key role in regulating intracellular O 2 ( Shimakawa et al, 2020 ) and could potentially also be considered a potential engineering target. Eventually, the expression of oxygen-binding proteins has also been proven to reduce hydrogenase inhibition.…”

The Great Oxidation Event (GOE): Biogeochemical Feedback and Tipping Points

“…They share the same metabolic pathway, the thylakoid membrane, for electron transfer (Kirchhoff, 2014). The molecule that carries the electrons, plastoquinone, functions as a redox sensor that drives the magnitude and direction of the transfer to maintain metabolic and redox homeostasis (Havaux, 2020;Shimakawa et al, 2021). Respiration supplies metabolic energy to the cell during the night, and it protects the cell from excess oxygen during the day.…”