Microbial Electrochemical System: extracellular electron transfer from photosynthesis and respiration to electrode

Abstract

The electrochemical communication between microorganisms and electrodes has substantial implications both for basic understanding of biological electron transfer as well as in diverse applications, such as, microbial electrochemical system (MES), microbial biosensors and in production of valuable chemicals. In these systems the extracellular electron transfer (EET) from microbial metabolism to electrodes is restricted due to the insulated cellular exterior made of lipid structures. To obtain the electrochemical wiring of biomaterials with electrodes, osmium redox polymers (ORPs) was used as an efficient electron transfer (ET) mediator.



In this thesis a systematic study on EET from a variety of biomaterials is demonstrated. The EET from the most metabolically versatile purple bacterium, i.e., Rhodobacter capsulatus, grown under both heterotrophically and photoheterotrophically conditions was studied. Shewanella oneidensis MR-1 is a metal ion reducing bacterium and was highly studied in microbial electrochemical systems (MES) due to its direct ET competence. We have shown that S. oneidensis MR-1 can be coupled with ORP modified graphite electrodes that results in an enhanced current density.



A secured supply of cost effective sustainable energy is on of the greatest challenges in the 21st century. Biological photovoltaics (BPVs) is emerging as a potential energy generating technology to convert solar energy into electrical energy. To harness solar energy we studied the photo-excited EET from water oxidation via thylakoid membranes, the site of photosynthesis in green plants and algae. In addition three prokaryotic cyanobacteria, two different Leptolyngbya sp., and Chroococcales sp. were photo-electrochemically wired with electrodes. The photo-electrochemical communication of a multicellular eukaryotic alga was assumed to be challenging, since here photosynthesis occurs in a specially designed subcellular organelle called chloroplast. We have shown the photoelectrochemical communication of the eukaryotic alga, Paulschulzia pseudovolvox immobilized on a graphite electrode wired with ORPs.



Although a great deal of research is focussed on MES, however, to seek any potential practical application their performance due the low power output and restricted stability need to be improved many folds. Our findings could have substantial implications in MES, such as microbial fuel cells (MFC), microbial biosensors, photosynthetic energy generation and in other light sensitive bioelectrochemical devices.

Abstract (Swedish)

Popular Abstract in English

The global energy consumption is increasing regularly due to the increased population and economic development. In contrast the primary energy sources, fossil fuels, are declining substantially. The combustion of fossil fuels contributes to the global climate change via greenhouse effects. To minimize these negative effects a carbon-neutral energy production is demanded.



To guarantee a secured supply of a cost-effective sustainable clean energy production is one of the greatest challenges in the 21st century. Solar energy is the most abundant among all other renewable energy sources such as hydroelectricity, geothermal energy, and wind energy. Solar energy is the most ubiquitous around the world and the largest exploitable renewable energy resource. The amount of solar energy radiating from the sun to the earth in one hour is greater than the entire human annual global energy demand.



Biological photovoltaics (BPVs) is emerging as a potential energy generating technology, where photosynthetic organisms are used to convert solar energy into electrical energy. Photosynthetic organisms in BPVs use solar energy for photolysis of water and provide electrons to the system. They are self-sustainable, inexpensive to maintain their growth culture and stored respiratory metabolites inside the cells could be used to generate electrical energy even in the dark. However, the photo-excited extracellular electron transfer (EET) from photosynthetic organisms to electrodes is one of the great challenges in BPVs.



In this thesis we have studied the photo-electrochemical communication of various photosynthetic materials. We investigated the photo-excited EET from thylakoid membranes (TMs) from spinach, purple bacteria, and cyanobacteria as well as from eukaryotic algae. Besides that we have investigated the electrical wiring of heterotrophic microorganisms to electrodes for possible use in microbial electrochemical systems (MESs).



These findings could have significant impacts in photosynthetic energy conversion, light sensitive bioelectrochemical devices and in biological fuel generation.

• author: Hasan, Kamrul
• supervisor: Lo Gorton
• opponent: Professor Howe, Christopher, Department of Biochemistry, University of Cambridge, United Kingdom
• organization: Biochemistry and Structural Biology
• publishing date: 2016
• type: Thesis
• publication status: published
• subject: Analytical Chemistry
• keywords: Biological photovoltaics, electron transfer, electrode, Rhodobacter capslatus, thylakoid membranes, cyanobacteria, algae, photosynthesis, light, photocurrent, electrochemistry
• pages: 204 pages
• defense location: Chemical center, Lecture hall: A, Naturvetarvägen 14, Lund
• defense date: 2016-02-26 09:15:00
• ISBN: 978-91-7422-428-3
• language: English
• LU publication?: yes
• id: dbeee8f9-92b8-4c14-ac8a-2c25a92af1b3 (old id 8618116)
• date added to LUP: 2016-04-04 10:39:43
• date last changed: 2018-11-21 21:00:03