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

Abstract

Oxygenic photosynthetic organisms perform solar energy conversion of water and CO2 to O2 and sugar at a broad range of wavelengths and light intensities. These cells also metabolize sugars using a respiratory system that functionally overlaps the photosynthetic apparatus. In this study, we describe the harvesting of photocurrent used for hydrogen production from live cyanobacteria. A non-harmful gentle physical treatment of the cyanobacterial cells enables light-driven electron transfer by an endogenous mediator to a graphite electrode in a bio-photoelectrochemical cell, without the addition of sacrificial electron donors or acceptors. We show that the photocurrent is derived from photosystem I and that the electrons originate from carbohydrates digested by the respiratory system. Finally, the current is utilized for hydrogen evolution on the cathode at a bias of 0.65 V. Taken together, we present a bio-photoelectrochemical system where live cyanobacteria produce stable photocurrent that can generate hydrogen.

Design of Optimized PEDOT‐Based Electrodes for Enhancing Performance of Living Photovoltaics Based on Phototropic Bacteria

“…Under 100 µmol m −2 s −1 of illumination, the PEDOT‐DS electrode shows a ≈ sixfold enhancement of the photocurrent density compared to the bare graphite in the absence of mediator. Since Synechocystis cells do not produce significant quantities of endogenous mediators,24 direct electron transfer is believed to serve as the primary means of extracellular electron transfer in the absence of added mediator. Therefore, the observed enhancement under nonmediated conditions is attributed to an effective increase in the direct transfer of photosynthethically derived electrons.…”

“…Consequently, one of the most studied approaches for enhancing extracellular electron transfer is electrode materials engineering. Surface modifications can promote more intimate contact between the electrode and the living cells and boost device efficiencies through more efficient charge extraction from the microbe 21–24. Conducting polymers (CPs), such as polypyrrole, polyaniline, poly(3, 4‐ethylenedioxythiophene) (PEDOT), and their composites, have been deposited onto different electrode substrates to improve electron export in microbial fuel cells 21,22,25–29.…”

Effect of different irradiance levels on bioelectricity generation from algal biophotovoltaic (BPV) devices

“…[3][4][5][6][7] Instead of releasing carbon dioxide (CO 2 ), microalgae remove CO 2 from the surroundings for biomass production. 13 Some of the earliest algal BPV devices contained algal biofilms in the anodic chamber for bioelectricity generation. Microalgae have multiple protection mechanisms that shield the cells from sudden exposure to high irradiance but the deleterious consequences of excessive illumination over extended period of time can render the photoprotective mechanisms ineffective.…”

Optical Shading Induces an In‐Plane Potential Gradient in a Semiartificial Photosynthetic System Bringing Photoelectric Synergy

“…[10][11][12][13][14] The "biomimetic solar cell," an application long sought after, aims to mimic the architecture of nature's reaction center (RC) and light-harvesting (LH) complexes in a fully artificial photosynthetic device for direct "solar electricity" generation. [18] Alongside the development of artificial photosynthetic systems, there have also been attempts to directly employ natural photosynthetic materials such as bacterial cells, [19][20][21] pigment proteins, [22][23][24][25][26][27][28][29] and membranes [30,31] as photoactive components for both direct electricity generation and fuel molecule synthesis.While, on the one hand, fully artificial photosynthetic systems lack the nanoscale architectural sophistication found in natural photosystems, on the other hand, natural photosystems are not always sufficiently robust or efficient outside their native environments. [18] Alongside the development of artificial photosynthetic systems, there have also been attempts to directly employ natural photosynthetic materials such as bacterial cells, [19][20][21] pigment proteins, [22][23][24][25][26][27][28][29] and membranes [30,31] as photoactive components for both direct electricity generation and fuel molecule synthesis.…”

“…These and other factors limit the performance of a device employing solely natural or artificial materials as the photoactive component. [34,35] Direct electric current generation has also been studied in a wide variety of biohybrid devices, combining different photosynthetic microorganisms [19,20,36] and Semiartificial photosynthetic systems have opened up new avenues for harvesting solar energy using natural photosynthetic materials in combination with synthetic components. [32,33] The concept has already shown signs of success in fuel generation by photo-electrochemical water splitting.…”