Electrochemical Communication Between Electrodes and Rhodobacter capsulatus Grown in Different Metabolic Modes

Abstract

The majority of efforts on microbial and photosynthetic microbial fuel cells are both curiosity driven and made to possibly meet the future growing demand for sustainable energy. The most metabolically versatile purple bacteria Rhodobacter capsulatus is a potential candidate for this purpose. However, utilizing bacteria in such systems requires efficient electronic transfer communication between the microbial cells and the electrodes, which is one of the greatest challenges. Previous studies demonstrated that osmium redox polymers (ORPs) could be used for extracellular electron transfer between the cells and electrodes. Recently, heterotrophically grown R. capsulatus has been wired with ORP modified electrodes. Here in this communication, we report electron transfer from R. capsulatus grown under heterotrophic as well as under photoheterotrophic conditions to electrodes. The cells, immobilized on bare graphite and ORP modified graphite electrodes, were excited with visible light and subsequent photosynthetic electron transfer was recorded using cyclic voltammetric and chronoamperometric measurements. Photoheterotrophically grown R. capsulatus cells on bare graphite generate a significant photocurrent density of 3.46 µA cm−2, whereas on an ORP modified electrode the current density increases to 8.46 µA cm−2. Furthermore, when 1 mM p‐benzoquinone is added to the electrolyte the photocurrent density reaches 12.25 µA cm−2. Our results could have significant implications in photosynthetic energy conversion and in development of photobioelectrochemical devices.

Photoelectrochemical Wiring of Paulschulzia pseudovolvox (Algae) to Osmium Polymer Modified Electrodes for Harnessing Solar Energy

“…Graphite electrodes were modifi ed with 5 µL of [Os(2,2′-bipyridine) 2 (polyvinylimidazole) 10 Cl] +/2+ , (Os-(bpy)PVI) (1:9)(E°´ = +0.22 V) [ 38 ] and CVs were recorded in the presence and absence of illumination ( Figure 2 ). Previously, a similar change in response was observed with both Rhodobacter capsulatus [ 22 ] and cyanobacteria on Os-polymer modifi ed graphite electrodes. KCl) is observed in the absence of illumination, in close agreement with previous reports on this polymer.…”

“…[ 6 ] The greatest benefi t of using the above-mentioned exogenous mediators is the simplicity while selecting microorganisms as well as electrode materials. Recently, Os-polymers were studied as electron conduits between photosynthetic organisms ( Rhodobacter capsulatus [ 22 ] and Leptolyngbya sp. [ 14 ] Instead, surface confi ned fl exible osmium containing redox polymers (Os-polymers) have already been successfully used as effi cient mediators in enzymatic biosensors, providing electron conduits between enzyme active sites and electrode surfaces.…”

Mechanism and analyses for extracting photosynthetic electrons using exogenous quinones — what makes a good extraction pathway?

“…Although all involve obviously an electrode for collecting the electrons from the photosynthetic organism, the nature of the biological target and the experimental conditions are rather various. [20][21][22][23] In a previous study based on fluorescence measurements, we characterized the ability of several quinones to extract photosynthetic electrons from Photosystem II (PSII) in a mutant strain of Chlamydomonas Reinhardtii which lacks the cytochrome b 6 f complexes (b 6 f mutant), thus being unefficient to utilize electrons photoproduced by Photosystem II. 3,4 In that case, using a redox polymer, nanoparticles or nanotubes has been demonstrated to help the photosynthetic electrons shuttle from the photosynthetic chain to the electrode.…”

Evaluation of Photocurrent Generation from Different Photosynthetic Organisms

“…Instead intact photosynthetic organisms are self‐sustainable and can self‐repair in diverse environmental conditions . Therefore, a range of photosynthetic organisms are exploited in BPVs including purple bacteria, prokaryotic cyanobacteria, and eukaryotic algae . Purple bacteria are less preferable in BPVs, since they require provision with organic and or inorganic substrates as electron donors …”