Photosynthetic Membranes of Synechocystis or Plants Convert Sunlight to Photocurrent through Different Pathways due to Different Architectures

Abstract

Thylakoid membranes contain the redox active complexes catalyzing the light-dependent reactions of photosynthesis in cyanobacteria, algae and plants. Crude thylakoid membranes or purified photosystems from different organisms have previously been utilized for generation of electrical power and/or fuels. Here we investigate the electron transferability from thylakoid preparations from plants or the cyanobacterium Synechocystis. We show that upon illumination, crude Synechocystis thylakoids can reduce cytochrome c. In addition, this crude preparation can transfer electrons to a graphite electrode, producing an unmediated photocurrent of 15 μA/cm2. Photocurrent could be obtained in the presence of the PSII inhibitor DCMU, indicating that the source of electrons is QA, the primary Photosystem II acceptor. In contrast, thylakoids purified from plants could not reduce cyt c, nor produced a photocurrent in the photocell in the presence of DCMU. The production of significant photocurrent (100 μA/cm2) from plant thylakoids required the addition of the soluble electron mediator DCBQ. Furthermore, we demonstrate that use of crude thylakoids from the D1-K238E mutant in Synechocystis resulted in improved electron transferability, increasing the direct photocurrent to 35 μA/cm2. Applying the analogous mutation to tobacco plants did not achieve an equivalent effect. While electron abstraction from crude thylakoids of cyanobacteria or plants is feasible, we conclude that the site of the abstraction of the electrons from the thylakoids, the architecture of the thylakoid preparations influence the site of the electron abstraction, as well as the transfer pathway to the electrode. This dictates the use of different strategies for production of sustainable electrical current from photosynthetic thylakoid membranes of cyanobacteria or higher plants.

Live cyanobacteria produce photocurrent and hydrogen using both the respiratory and photosynthetic systems

“…When we measured current over time (chronoamperometry, CA), at an applied potential of 150 mV (vs. Ag/AgCl/3 M NaCl) (standard working potential obtained from the IV curve (Supplementary Fig. 1A ), for all CA experiments unless mentioned otherwise), a dark current of 5 ± 1 µA cm −2 was obtained, probably directly from the respiratory system, as previously suggested 36 , 37 (Fig. 2b , initial 100 seconds).…”

NADPH performs mediated electron transfer in cyanobacterial-driven bio-photoelectrochemical cells

“…This problem can be solved by performing mediated electron transfer (MET) with mediators that are able to cross these barriers and efficiently interact with either inorganic or metallic electrodes and photosynthetic biological components. Previous studies have used exogenously added mediators such as ferricyanide ( Huang et al., 2015 ; Lan et al., 2013 ; Laohavisit et al., 2015 ; McCormick, 2011 , 2013 ; Ochiai et al., 1983 ), 2,6-dichloro-1,4 benzoquinone ( Calkins et al., 2013 ; Larom et al., 2010 ; Pinhassi et al, 2015 , 2016 ; Sekar et al., 2014 ; Tanaka et al., 1985 ), 2-hydroxy-1,4-naphthoquinone ( Tanaka et al., 1988 ; Torimura et al., 2001 ; Yagishita et al., 1993 ; Zou et al, 2009 , 2010 ), or 1,4-benzoquinone ( Longatte et al., 2018 ; Sekar et al., 2014 ). However, all bacteria, and especially cyanobacteria, have outer membranes that limit the ability of such molecules to enter and exit the cells.…”

Diverting photosynthetic electrons from suspensions of Chlamydomonas reinhardtii algae - New insights using an electrochemical well device

“…This is why isolated thylakoid membranes or chloroplasts are also considered. [8][9][10][11][12] Yet, the lack of cell proliferation of these two strategies is an important issue and pushes toward the investigation of intact photosynthetic organisms. [13][14][15][16][17] However, the more complex the target is, the more difficult is the electron transport ways toward the electrode.…”