The metabolically versatile bacterium Shewanella oneidensis adapts to anaerobic environments by transporting electrons to its exterior, reducing a variety of environmental substrates. When grown anaerobically and provided with lactate as a carbon source, S. oneidensis transfers electrons to an electrode of a microbial fuel cell. We sought to engineer S. oneidensis to report variations in environmental conditions through changes in current production. A previous study has shown that S. oneidensis mutants deficient in the mtrB gene produce less current than the wildtype strain, and that current production in these mutants can be restored by the addition of exogenous mtrB. We attempted to control current production in mtrB knockouts by introducing mtrB on lactose, tetracycline, and heat inducible systems. These novel biosensors integrate directly with electrical circuits, paving the way for the development of automated, biological measurement and reporter systems.
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The 2008 Harvard iGEM project is based on the ability to control and measure the electric current production in Shewanella oneidensis MR-1. Multiple genes in Shewanella have been identified as playing a role in transferring electrons to solid substrates, thus generating an easily detectible electric current. Our goal is to be able to detect differences in current output by the activation and/or deactivation of these genes in Shewanella. To do this, we are using mutant strains of Shewanella which have one or more of these important electron transfer genes knocked out and are reintroducing the genes on an inducible plasmid. The electric current produced will be detected by a multimeter, and read by a computer, creating a computer-biology interface.
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We are developing two inducible systems for electrical current production in Shewanella. The first is a chemically inducible system, where LacI or TetR repression of the current-production gene expression can be alleviated by the addition of IPTG or anhydrotetracycline, respectively. Our second approach is a light-inducible system based on the 2005 UT Austin biological camera. We are also considering a third approach using cI lambda which would be dependent on temperature.
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Using one or both of these systems, we hope to be able to interact with engineered Shewanella in multiple anaerobic microbial fuel cells which we have built. Communication between the fuel cells and a computer then has the potential to be programmable into a game of sorts, such as Tic-Tac-Toe, in which the level of current production induced by a chemical or light input is understood by the computer as a "turn." This rudimentary game is just one of many possibilities for an inducible interaction between computers and bacteria.
The metabolically versatile bacterium Shewanella oneidensis adapts to anaerobic environments by transporting electrons to its exterior, reducing a variety of environmental substrates. When grown anaerobically and provided with lactate as a carbon source, S. oneidensis transfers electrons to an electrode of a microbial fuel cell. We sought to engineer S. oneidensis to report variations in environmental conditions through changes in current production. A previous study has shown that S. oneidensis mutants deficient in the mtrB gene produce less current than the wildtype strain, and that current production in these mutants can be restored by the addition of exogenous mtrB. We attempted to control current production in mtrB knockouts by introducing mtrB on lactose, tetracycline, and heat inducible systems. These novel biosensors integrate directly with electrical circuits, paving the way for the development of automated, biological measurement and reporter systems.
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