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Missing abstract
The world is changing and so are the energy needs of humanity. Fossil resources are being depleted and it is clear that the transition to clean sustainable energy has to be made. We believe synthetic biology can be an important catalyst in this process. Specifically, we engineer a Bacillus subtilis biofilm to function as a cation exchange membrane. Such a membrane can be used in Reverse Electrodialysis (RED), a technique to generate energy where salt and fresh water mix, for example where rivers flow into the sea. We call this application of the bacterial biofilm Blue Bio Energy. To make the Bacillus subtilis suitable for RED, we first make it more robust by overexpressing the biofilm genes tasA and bslA while preventing reversion to the motile state by knocking out the abrB regulator and overexpressing slrR, another biofilm regulator. Simultaneously, the amino acid polymer gamma-polyglutamic acid was modelled extensively to see if it could be used to make the biofilm ion selective. This was found to be the case. Experiments showed that Bacillus subtilis 3610 comI biofilms are slightly ion selective and, surprisingly, that ion selectivity is improved by knocking out abrB as well as by overexpression of bslA and slrR.
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Carrier on which the biofilm grows
Our biofilm was grow on a carrier material for strength and durability. Whatman paper was chosen for its great biofilm growth and low cost. Four growth methods were studied to optimize biofilm growth and strength.
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Biofilm ion selectivity
The ion selectivity for Na+ and Cl- of a membrane of negatively charged γ-PGA molecules was modelled using Molecular Dynamics. Wetlab testing was performed using B. subtilis Natto.
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Rigidity of the biofilm
To survive water flow, the biofilm has to be stable and robust. This was done by overexpressing genes involved in biofilm formation and by knocking out genes having the opposite effect.
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New shuttle vector
An extra integration locus for Bacillus, such as the thrC locus, is welcome when making a multiple mutant. The amyE locus parts of the BBa_K823023 backbone were replaced with the thrC locus parts from the plasmid pDG1664, resulting in a new shuttle vector.
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Human Practices
When working with GMOs, it is important to know the regulations and to think about the final application and the response of the public. To address this, we visited COGEM, designed an educational card game and considered several future scenarios involving GMOs and our project.
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Future perspective
Our bacteria need to stay and survive in the power plant. Ideally, the bacteria cannot escape, and the biofilm is sustained by using the nutrients present in water.