Electron transport in cyanobacterial thylakoid membranes: are cyanobacteria simple models for photosynthetic organisms?

This article reviews the molecular mechanisms and in vivo activities of electron transport in cyanobacterial thylakoid membranes, focusing on the complex interplay between photosynthetic and respiratory processes that share common components. It highlights photosynthetic linear electron transport (LET) as the primary pathway for CO2 assimilation, alongside significant alternative electron transport routes such as O2 photoreduction mediated by flavodiiron proteins (Flv), respiratory electron transport (RET) via a homologue of respiratory complex I (NDH-1L), and O2-independent pathways involving hydrogenase and nitrate reductase. The review also discusses the challenges in distinguishing cyclic electron transport (CET) from RET in vivo and emphasizes the regulatory complexity arising from the shared electron carriers and metabolic integration within cyanobacterial cells. Despite advances in characterizing individual pathways, the overall regulation and physiological significance of their interactions remain incompletely understood, with most knowledge derived from a few model cyanobacterial species.