title: Electrochemical Detection of Circadian Redox Rhythm in Cyanobacterial Cells via Extracellular Electron Transfer.
abstract: Recent research on cellular circadian rhythms suggests that the coupling of transcription-translation feedback loops and intracellular redox oscillations is essential for robust circadian timekeeping. For clarification of the molecular mechanism underlying the circadian rhythm, methods that allow for the dynamic and simultaneous detection of transcription/translation and redox oscillations in living cells are needed. Herein, we report that the cyanobacterial circadian redox rhythm can be electrochemically detected based on extracellular electron transfer (EET), a process in which intracellular electrons are exchanged with an extracellular electrode. As the EET-based method is non-destructive, concurrent detection with transcription/translation rhythm using bioluminescent reporter strains becomes possible. An EET pathway that electrochemically connected the intracellular region of cyanobacterial cells with an extracellular electrode was constructed via a newly synthesized electron mediator with cell membrane permeability. In the presence of the mediator, the open circuit potential of the culture medium exhibited temperature-compensated rhythm with approximately 24 h periodicity. Importantly, such circadian rhythm of the open circuit potential was not observed in the absence of the electron mediator, indicating that the EET process conveys the dynamic information regarding the intracellular redox state to the extracellular electrode. These findings represent the first direct demonstration of the intracellular circadian redox rhythm of cyanobacterial cells.
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan.
authors.forename: Koichi
authors.initials: K
authors.lastname: Nishio
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan.
authors.forename: Tunanunkul
authors.initials: T
authors.lastname: Pornpitra
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan.
authors.forename: Seiichiro
authors.initials: S
authors.lastname: Izawa
authors.affiliation: Institute of Transformative Bio-Molecules (WPI-ITbM), Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8602 Japan.
authors.forename: Taeko
authors.initials: T
authors.lastname: Nishiwaki-Ohkawa
authors.affiliation: Research Center for Advanced Science and Technology, The University of Tokyo, 4-6-1 Komaba, Meguro-ku, Tokyo, 153-8904 Japan Bioproduction Research Institute, National Institute of Advanced Industrial Science and Technology, 2-17-2-1 Tsukisamu-Higashi, Toyohira-ku, Sapporo, Hokkaido, 062-8517 Japan.
authors.forename: Souichiro
authors.initials: S
authors.lastname: Kato
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan.
authors.forename: Kazuhito
authors.initials: K
authors.lastname: Hashimoto
authors.affiliation: Department of Applied Chemistry, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo, 113-8656 Japan nakanishi@light.t.u-tokyo.ac.jp.
authors.forename: Shuji
authors.initials: S
authors.lastname: Nakanishi
mesh_terms: D002940:Circadian Rhythm; D055664:Electrochemical Techniques / Q000379:methods*; D004579:Electron Transport; D005110:Extracellular Space / Q000378:metabolism*; D005453:Fluorescence; D010084:Oxidation-Reduction; D045332:Photosystem II Protein Complex / Q000378:metabolism; D018892:Proton-Motive Force; D046940:Synechococcus / Q000166:cytology* / Q000378:metabolism*; D013696:Temperature; D013997:Time Factors
chemical_list: D045332:Photosystem II Protein Complex
keywords: Circadian clock; Cyanobacteria; Electrochemistry; Extracellular electron transfer; Redox rhythm