Microbial electro-photosynthesis
Methods and apparatus for growing photosynthetic organisms lacking Photosystem II (PSII) function using externally supplied electrons shuttled into the organism using redox mediators to improve photosynthetic output and to produce and recover chemicals of interest. By removing PSII, all PAR photons are funneled toward Photosystem I, thereby significantly increasing the theoretical photon utilization efficiency for CO 2 fixation, energy storage and the capacity to synthesize valuable chemicals. Additional genetic modification can be performed to insert or enhance specific metabolic pathways to generate products of commercial interest.
1. A microbial electrosynthesis cell apparatus comprising:
a photobioreactor;
a liquid disposed within the photobioreactor containing cyanobacterium comprising a mutation in a gene encoding a protein of Photosystem II (PSII), wherein PSII function in said cyanobacterium is minimal or absent;
an electrode unit comprising an anode and a cathode, wherein the electrode unit is in fluid communication with the photobioreactor;
a power source coupled to the electrode unit
wherein, a source of electrons is generated in the electrode unit; and
a redox mediator for shuttling electrons between the mutant cyanobacterium and the cathode.
2. The apparatus of claim 1 wherein the photobioreactor is selected from the group consisting of a vertical tubular, air-lift, horizontal tubular, flat-panel, or plastic-bag photobioreactor.
3. The apparatus of claim 1 wherein the anode further comprises a catalyst to promote water oxidation to generate the electrons.
4. The apparatus of claim 3 , wherein said catalyst is selected from the group consisting of platinum, platinum-carbon, cobalt phosphate, Co 3 O 4 nanoparticles, and Co 2 O 3 nanoparticles.
5. The apparatus of claim 1 wherein the cathode further comprises carbon felt or carbon fiber.
6. The apparatus of claim 1 wherein the cyanobacterium comprises mutant cyanobacterium Synechocystis sp. PCC 6803 with no or minimal PSII function.
7. The apparatus of claim 1 , wherein the power source is a photovoltaic device.
8. The apparatus of claim 7 , wherein the photovoltaic device is located beneath the photobioreactor and configured to produce electricity using the light not absorbed by the cyanobacterium.
9. The apparatus of claim 1 , wherein the source of electrons is provided by one or more of the group consisting of water oxidation, water electrolysis, hydrogen gas, hydrogen sulfide, the breakdown of organic waste, metal corrosion, cultures of anode respiring bacteria (ARB) and non-ARBs such as fermenters and methanogens that syntrophically breakdown organic waste.
10. The apparatus of claim 1 , wherein the electrons are shuttled to the cyanobacterium using a redox mediator selected from the group consisting of duroquinone, trimethylquinone, 2,5 dimethylquinone, 2,6 dimethylquinone, 2,3 dimethylquinone, benzoquinone, 2,6-di-tert-butyl-1,4-benzoquinone, or ubiquinone.
11. The apparatus of claim 1 , wherein the external electrons are shuttled to the cyanobacterium using a redox mediator selected from the group consisting of a plastoquinone (PQ) variant, where the native isoprenoid tail of PQ is replaced with an alkyl tail of 2, 3, 4, 5, 6, 7, 8 or 9 carbons.
12. The apparatus of claim 1 , wherein the external electrons are shuttled to the cyanobacterium using a redox mediator selected from the group consisting of methylene blue, thionine, rezasurin or a protein redox mediator.
13. The apparatus of claim 1 , wherein the electrode unit is configured to transfer reduced redox mediators into the photobioreactor and the photobioreactor is configured to transfer oxidized redox mediators back to the electrode unit.
14. The apparatus of claim 1 , wherein the cathode is porous such that transfer of reduced redox mediators and oxidized redox mediators through the cathode occurs.