Background
In fields such as nano-scale robotics and manufacturing researchers have encountered problems in generating motion and force reliably. In recent years many attempts have been made at using micro-organisms to create useable mechanical force. Many approaches have been taken including using swimming bacteria to drive microgears, move objects and to generate organised flow on surfaces and in pump-like systems. Different attempts at introducing remote control in such systems have also been made using magnetism, chemical signalling and light. It seems obvious how synthetic biology and bio-engineering might contribute by creating systems for these purposes.
The Idea
Inspired by an article on flow generated in a micro-capillary tube by a bacterial "pump" [http://microfluids.engin.brown.edu/Breuer_Papers/Journals/Small2008_Bacterial_Pump.pdf]
we have decided to attempt construction of a similar system. Our approach centers on E. coli that will be modified to overexpress flagella, in an attempt to increase force generation potential. These bacteria will be attached to a surface, and their flagella should therefore generate flow in the surrounding liquid. We also want to be able to regulate the flow that is generated, both in strength and direction.
Regulation of the pump will be introduced through a photo-sensing chimeric fusion protein that has recently been shown to integrate with the E. coli chemotaxis system [http://pubs.acs.org/doi/abs/10.1021/bi034399q], to control tumbling frequencies in our bacteria, thereby giving us control over the amount of turbulence disrupting our pump via a blue light source. This will result in an off-switch, since the blue light increases the tumbling frequency, which disturbs the flow. The more bacteria tumble instead of following the "run" pattern, the weaker (or nonexistent) the flow woll be. The parts contributed will in effect introduce phototaxic ability to E. coli.
For the photoreceptor to work, we will need to supply it with retinal. Therefor we will be building on work done in the Cambridge 2009 project, that introduced beta-carotene synthesis in E. coli, and contribute an enzyme that will catalyze cleavage of beta-carotene into retinal. By this our biological machine can supply it self with everything it needs to function, so that once the system has been established, there is need to intervene (except for the light regulation).
On top of creating a microfluidic flow generator, we will hopefully at the same time create a system that can mix fluids in microtubes. It is often a problem when working with tubes of this dimension, that if you let two liquids flow into them, they will not mix. The turbulence created by the bacteria's flagella will make both liquids move around randomly in the tube, so that they will become one in the end.
The plan is that these three subprojects will result in a biobrick each:
- A constitutively active operon with the master regulator of flagella synthesis.
- A bluelight photosensor coupled to the chemotaxis pathway.
- A generator for the enyzme that cleaves beta-carotene to retinal.
For further details and closer descriptions, please visit the "Theory" section.
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