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Abstract

The growing need for alternative fuel sources has sparked interest and research across many scientific and engineering disciplines. The fledgling field of microbial fuel cell development has previously relied on anaerobic metal reducing organisms such as Geobacter sulfurreduccens. This project sought to isolate genes from the electron shuttling pathway in Geobacter and transform them into the more manageable aerobic Escherichia coli. The Missouri University of Science and Technology iGEM team isolated four outer membrane cytochrome (omc) genes from Geobacter, vital to the extracellular transportation of electrons. The four genes; omcB, omcE, omcS and omcT, were cloned into individual plasmids. The eventual goal is to combine all four genes into one plasmid to transform into E. coli to create an aerobic, electron transporting microbial system.

Background

Currently the iGEM team is focusing on a single project, involving the transfer of an electron shuttling pathway from Geobacter sulfurreducens to Escherichia coli. The initial project began with a desire for researchers’ to overcome the limitations of doing microbial fuel cell research in anaerobic bacteria. Due to the anaerobic nature of G. sulfurreducens, fuel cell research conducted using the bacterium requires an elaborate setup and the fuel cell being completely oxygen free. This is achieved by having a constant flow of nitrogen into the fuel cell. Moving the electron shuttling pathway into a facultative aerobic bacterium allows for a less complex system and also helps facilitate useful commercial applications of the research.

Dr. Derek Lovely’s extensive and ongoing research on the electron shuttling pathway in G. sulfurreducens and other electricigens has served as a springboard for the team’s project. Lovely identified four outer membrane cytochromes either necessary for or highly involved in transport of electrons to the outside of the cell. Through the iGEM team’s work, these cytochromes will form the critical bridge between the highly efficient oxidation processes of aerobic bacterium such as E. coli and the anodic environment of the microbial fuel cell.

The corresponding outer membrane cytochrome genes omcB, omcE, omcS, and omcT were individually isolated from G. sulfurreducens and transformed into E. coli. These genes were each cloned into new plasmids providing a ribosome binding site sequence, and are now in the process of being combined into a single plasmid containing all four genes and their respective ribosome binding sites. Current efforts are focused on finishing the gene combination process as well as testing the potential output of cells containing various combinations of the omc genes.

Process in Detail

Outer membrane cytochrome genes from Geobacter sp. omcB, omcE, omcS, and omcT were first obtained as nonfunctional sequences in plasmids from the iGEM standard registry of parts (parts BBa_K269000 through BBa_K269003).

These genes were each combined to a ribosome binding site (RBS) promoter part BBa_J61100.

Through a series of digestions, ligations, and transformations, three of these functional genes, B, E, and T, were combined to form part BBa_K306000.

In the future, the omcS gene will be added to create a plasmid containing all four omc genes.

Relevant Links:

• Microbial Fuel Cells
• Wikipedia Article
• Geobacter Research
• Fuel Cells from Rhodopherax