Abstract
Oxygenic photosynthesis conducted by cyanobacteria has dramatically transformed the geochemistry of our planet. These organisms have colonized most habitats, including extreme environments such as the driest warm desert on Earth: the Atacama Desert. In particular, cyanobacteria highly tolerant to desiccation are of particular interest for clean energy production. These microorganisms are promising candidates for designing bioelectrodes for photocurrent generation owing to their ability to perform oxygenic photosynthesis and to withstand long periods of desiccation. Here, we present bioelectrochemical assays in which graphite electrodes were modified with the extremophile cyanobacterium Gloeocapsopsis sp. UTEXB3054 for photocurrent generation. Optimum working conditions for photocurrent generation were determined by modifying directly graphite electrode with the cyanobacterial culture (direct electron transfer), as well as using an Os polymer redox mediator (mediated electron transfer). Besides showing outstanding photocurrent production for Gloeocapsopsis sp. UTEXB3054, both in direct and mediated electron transfer, our results provide new insights into the metabolic basis of photocurrent generation and the potential applications of such an assisted bioelectrochemical system in a worldwide scenario in which clean energies are imperative for sustainable development.
Highlights
The environmental consequences of the current dependency of worldwide economy on fossil fuels have brought attention to alternative energy sources, among which solar energy-based photovoltaics represent the most appealing one
After 4 weeks of desiccation, the percentage of fluorescein diacetate (FDA) + cells fall to only 15%, a situation that became reverted once rehydration of the culture occurred, increasing FDA + cells to 50% of the whole population within 1 h
Our results indicate that the generated current density is associated to electron flux of cyanobacterial photosynthesis (Figure 4B)
Summary
The environmental consequences of the current dependency of worldwide economy on fossil fuels have brought attention to alternative energy sources, among which solar energy-based photovoltaics represent the most appealing one. The exchange of electrons from the cyanobacterial electron transport chain to external electrodes is not a simple task Aiming to optimize this process, cyanobacteria have been grown or dried on the top electrodie surfaces (McCormick et al, 2011; Cereda et al, 2014; Sekar et al, 2016; Wei et al, 2016). Once the electrode was dry, direct electron transfer (DET) was estimated after adding 5 μl of PEGDGE (1 mg ml−1 solution) and 20 μl of resuspended cyanobacteria on the electrode surface (cultures were prepared to final bacterial concentration of 2.3 × 106 cells ml−1). A flexible lamp illuminated the working electrode surface with a light intensity of 44 mW cm−2 This light allowed excitation of the photosynthetic activity of Gl. All electrochemical measurements were carried out using a PalmSens potentiostat equipped with the PSTrace software for instrument control and data acquisition. ANOVA was performed to analyze the differences between the photocurrent densities ( J) using Excel software
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