As a way to extend the applications of our biosensor we decided to think about environmentally friendly biodegradable papers. This led us to microbial cellulose as it is inexpensive to produce and can break down easily into glucose. At the same time, the Stanford-Brown 2015 iGEM project focused on reducing the mass and volume of supplies required to send on space missions by making self-folding biological materials called biOrigami. They are seeking to incorporate sheets of microbial cellulose produced from Gluconacetobacter hansenii into their project as one of their folding mechanisms.

In an effort to improve these sheets, they are processing them which could affect their properties. From there, they are experimenting with attaching bacterial spores to sheets of the microbial cellulose, and then using the contractile properties of these spores in the presence of differing relative humidities to cause the sheets to bend. To attach the spores to the cellulose, they are attempting to express cellulose binding domains (CBDs) on the spore coats. The sheets of microbial cellulose that they processed and gave us allowed us to compare the usefulness of the microbial cellulose as a basis for a biosensor through our experiments in testing the binding affinities of a CBD on both processed and unprocessed sheets. In turn, our experiments testing the binding affinities helped guide the Stanford-Brown choice of cellulose processing technique for making sheets to which the spores will attach.

For this collaboration we expanded on the characterisation of BBa_K1321357 which is sfGFP fused to CBDcex driven by LacI and used our dissociation protocol. We chose this specific CBD because it was in the distribution kit with enough characterisation to ensure that the only variable we are testing is the processed vs unprocessed cellulose. As you can see on the graph, there are large error bars however there is a clear difference between the binding on the processed and unprocessed sheets of microbial cellulose. This could be because the processing may get rid of any remaining organisms or proteins that would inhibit the CBD binding. Due to limited time and cellulose sheets from the Stanford-Brown team, we were unable to repeat this experiment.

From these results we would have to conclude that if we were to make a microbial cellulose based biosensor, it is best that it uses the processed sheets. From this we also advise the Stanford-Brown team to use the processed sheets. Due to the higher binding affinity of the CBD to the processed sheets, they should be able to have the spores stick for folding. Check out their project and how they processed the cellulose!

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