Specific Interaction between Redox Phospholipid Polymers and Plastoquinone in Photosynthetic Electron Transport Chain

Abstract

Redox phospholipid polymers added in culture media are known to be capable of extracting electrons from living photosynthetic cells across bacterial cell membranes with high cytocompatibility. In the present study, we identify the intracellular redox species that transfers electrons to the polymers. The open-circuit electrochemical potential of an electrolyte containing the redox polymer and extracted thylakoid membranes shift to positive (or negative) under light irradiation, when an electron transport inhibitor specific to plastoquinone is added upstream (or downstream) in the photosynthetic electron transport chain. The same trend is also observed for a medium containing living photosynthetic cells of Synechococcus elongatus PCC7942. These results clearly indicate that the phospholipid redox polymers extract photosynthetic electrons mainly from plastoquinone.

Electrochemical biotechnologies minimizing the required electrode assemblies

“…Nishio et al [23] developed electron-mediating co-polymers consisting of a hydrophilic phospholipid-like domain and a hydrophobic, redox-active vinylferrocene domain. This amphipathic mediator showed low cytotoxicity and enabled a diverse range of microorganisms to exchange electrons with electrodes [23,24]. Using the new amphipathic mediator, this laboratory achieved enhancement of polyhydroxybutyrate production by Ralstonia eutropha [25] and control of the circadian rhythms of photosynthetic cyanobacteria [26], clearly demonstrating the practical feasibility of this technology.…”

Rewiring photosynthetic electron transport chains for solar energy conversion

“…Polymers are considered less cytotoxic to in vivo R-PETCs than diffusible mediators, enhancing the stability of R-PETCs 7 . However, the limited access polymers have to intracellular environments limits their ability to interface with PETCs, though this has been overcome with polymers capable of traversing lipid membranes 143 . They can be used in a complementary manner with diffusional mediators to enhance the overall rewiring efficiency.…”

“…Photoelectrosynthesis can be achieved by injecting electrons into R-PETCs from a cathode (Fig. 5c), which can be achieved directly in ex vivo R-PETCs 45,143 , or via EEU pathways 86,184 or electron mediators 119 in in vivo R-PETCs. Photoelectrosynthesis allows for biocatalytic processes to be driven by electron donors PETCs are normally unable to utilise 17 .…”