Hydrogen production through oxygenic photosynthesis using the cyanobacterium Synechocystis sp. PCC 6803 in a bio-photoelectrolysis cell (BPE) system

Abstract

Microbial electrolysis cells (MECs) represent an emerging technology that uses heterotrophic microbes to convert organic substrates into fuel products, such as hydrogen gas (H 2). The recent development of biophotovoltaic cells (BPVs), which use autotrophic microbes to produce electricity with only light as a substrate, raises the possibility of exploiting similar systems to harness photosynthesis to drive the production of H 2. In the current study we explore the capacity of the cyanobacterium Synechocystis sp. PCC 6803 to generate electrons by oxygenic photosynthesis and facilitate H 2 production in a twochamber bio-photoelectrolysis cell (BPE) system using the electron mediator potassium ferricyanide ([Fe(CN) 6 ] 3À). The performance of a wild-type and mutant strain lacking all three respiratory terminal oxidase activities (rto) was compared under low or high salt conditions. The rto mutant showed a decrease in maximum photosynthetic rates under low salt (60% lower P max than wild-type) but significantly increased rates under high salt, comparable to wild-type levels. Remarkably, rto demonstrated a 3-fold increase in (Fe[CN] 6) 3À reduction rates in the light under both low and high salt compared to the wild-type. Yields of H 2 and efficiency parameters were similar between wild-type and rto, and highest under high salt conditions, resulting in a maximum rate of H 2 production of 2.23 AE 0.22 ml H 2 l À1 h À1 (0.68 AE 0.11 mmol H 2 [mol Chl] À1 s À1). H 2 production rates were dependent on the application of a bias-potential, but all voltages used were significantly less than that required for water electrolysis. These results clearly show that production of H 2 using cyanobacteria is feasible without the need to inhibit photosynthetic O 2 evolution. Optimising the balance between the rates of microbialfacilitated mediator reduction with H 2 production may lead to long-term sustainable H 2 yields. Broader context box Bioelectrochemical systems have emerged as a promising technology for energy recovery and the production of valuable fuel products such as H 2 gas. In microbial electrolysis cells (MECs), heterotrophic bacteria consume organic compounds to drive the electrochemical production of H 2. Here we report a twochamber bio-photoelectrolysis cell (BPE) system for producing H 2 that uses light as a substrate. In the anodic compartment of the BPE the cyanobacterium Synechocystis sp. PCC 6803 was used to generate electrons by oxygenic photosynthesis, with H 2 produced in the cathodic compartment. In addition, we studied the effects of mutations abolishing the terminal oxidases of the respiratory electron transport chain, with the striking result that a mutant (rto) showed threefold higher rates of reduction of the electron mediator ferricyanide than the wild-type strain. This is one of the rst examples of O 2-evolving autotrophs being used to facilitate sustainable H 2 production without the need to inhibit photosynthetic O 2 evolution or establish anaerobic conditions in the culture medium. Further increase...

Phycobilisome-Deficient Strains of Synechocystis sp. PCC 6803 Have Reduced Size and Require Carbon-Limiting Conditions to Exhibit Enhanced Productivity

“…Therefore, drawing any reliable comparison between our results and those of Kwon et al (2013) is not possible. However, the olive mutant may be useful for applications that require higher photosynthetic capacity, such as the generation of hydrogen (McCormick et al, 2013) or electricity in a biophotovoltaic device (Bombelli et al, 2011;Bradley et al, 2013).…”

Tapping into cyanobacteria electron transfer for higher exoelectrogenic activity by imposing iron limited growth

“…64 In this way, iron starvation could serve as a strategy for an integrated system with biomass growth for biodiesel production coupled to photo-bioelectricity generation. , 65 still less than a third of that achieved by the synergistic effect of neutral pH and iron limitation in wild-type PCC7942. FeCN-R rates obtained for iron sufficient PCC7942 at neutral pH, especially with young cultures, are similar to those achieved by Synechocystis sp.…”

Advances in Utilizing Cyanobacteria for Hydrogen Production

“…Recently, a system with anodic chamber containing whole cells of Synechocystis sp. PCC 6803 was tested [43]. Using (Fe[CN] 6 ) 3− as the electron mediator and platinum cathode, this device was able to produce 0.68 mmol H 2 /(mol chlorophyll × s) while 1.4 V biaspotential was applied.…”