Simultaneous Measurement of Gross Oxygen Evolution and Underlying Photosynthetic Redox Reactions: A Case Study Using Cyanobacteria

In phytoplankton, the intricate balance between respiration and photosynthesis is co-regulated to ensure efficient energy management and adaptation to varying environmental conditions. In cyanobacteria, both processes occur on the same membrane, sharing electron transport carriers within the same cellular compartment. By studying the interaction between photosynthesis and respiration, we can better understand how cyanobacteria balance their energetic budget for survival. In this study, we present an integrated approach that combines tracking gas exchange between cyanobacteria and their environment with analysing the redox kinetics of the underlying photosynthetic electron transport chain. This combined system allows for real-time, simultaneous acquisition of respiration and photosynthesis data. For example, it enabled us to show that the electron transport rate generated by photosystem II, translated to in-vivo oxygen concentration, equals the actual concentration of oxygen produced by water splitting plus the amount of oxygen respired. We further demonstrate that our system can accurately assess light respiration in wild-type strains of cyanobacteria, which amounts to 1/10 of their photosynthetic activity under optimal growth conditions. This level of accuracy was previously achievable only with specific cyanobacteria mutants. We envision applying this system in monitoring programs to elaborate on the role of photosynthetic light reactions within the broader context of primary productivity and to understand its dynamics in response to fluctuations in external environmental conditions.