Team:Cambridge/Project

Bactiridescence was based around the properties of reflectin, a squid protein with the highest refractive index of any known proteinaceous substance. In squid this protein forms complex platelets which act as Bragg reflectors to provide camouflage.

Contents 1 Project Goals 2 Microscopy 3 In Vitro 4 In Vivo 5 Conclusion and Future Work

Project Goals

We aimed to express reflectin in E. coli and to investigate its optical properties in order to build the groundwork for the manipulation of living structural colour. We also looked at the over-expression of reflectin in E. coli, in order to obtain relatively pure samples of the protein for making thin films.

Much of our work (particularly the in vivo work) simply hadn't been tried before, so, while we had high hopes, we could not be sure as to what would happen.

Microscopy

Initially we looked at some squid tissue using a confocal microscope, to see its morphological effect in squid cells.

In Vitro

When we over-expressed reflectin in E.Coli, we found (by making a GFP fusion) that while reflectin is surprisingly non-toxic to E.Coli, it formed inclusion bodies. We then extracted these inclusion bodies, purified the protein using a number of different techniques, and made thin films by spin-coating and flow-coating.

In Vivo

In order to express reflectin at lower levels, we made an arabinose-inducible version, both with and without a GFP-fusion. We found that at lower levels of expression, the reflectin-GFP fusion would not form inclusion bodies, but appeared to be uniformly distributed throughout the cell (see the Microscopy page) . We made several attempts to image this – hoping to find some change in optical properties – but found that while the induced cells did appear to exhibit iridescence, so did the uninduced. This, we theorise, is due to thin film interference around the cell wall and membrane.

We also attempted to export both our reflectin and our reflectin-GFP to the periplasm, in the hope that this environment would be more similar to the environment in which reflectin naturally folds and that the small space will promote reflectin's membrane-associating properties. As of writing, this has yet to be successful.

Conclusion and Future Work

Our project attempts to lay some groundwork for future research in to reflectins. Reflectin has numerous possible future applications, from display technologies to rapid bio-reporters.