Synchronous oscillation of photosynthetic electricity generation and carbon assimilation

Photosynthetic organisms generally exhibit oscillatory responses to environmental changes, including rapid increases in CO₂ concentration, decreases in O₂ concentration, or increases in light intensity. However, photosynthetic microorganisms such as cyanobacteria and microalgae generate electric current when exposed to light. The former and latter phenomena have garnered interest from the perspective of the response of photosynthetic regulatory systems to environmental changes and from the perspective of bio-photovoltaics, respectively. In the present study, we discovered that the photocurrent generated by cyanobacteria cultured on an anode oscillates with a period of several tens of seconds when suddenly exposed to light. Perturbations in environmental factors, the addition of inhibitors, and the use of genetic mutants revealed that the length of the oscillation period is influenced by the activity of carbon assimilation. In addition, quantitative analysis of intracellular metabolites indicated that the concentrations of some metabolites periodically change with similar period lengths as the photocurrent oscillations. These findings represent the first example of linking photosynthetic oscillations and bio-photovoltaics-two fields that have developed independently-and suggest that combining methodologies from each field could contribute to advancements in both.