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Archeal light receptor fused to bacterial chemotaxis transducer

Biological Background

Fusion of the Natronobacterium pharaonis Np seven-transmembrane retinylidene photoreceptor sensory rhodopsins II NpSRII and their cognate transducer HtrII to the cytoplasmic domain of the chemotaxis transducer EcTsr of Escherichia coli [1].

Rhodopsins are photoreactive, membrane-embedded proteins, which are found not only in archaea, but in eubacteria and microbes as well. In Natronobacterium pharaonis, the NpSRII contains a domain of seven membrane-spanning helices, which carry out two distinct functions: Firstly, they serve as photo-inducible ion-pumps and secondly, as actors in the chemotaxis signaling network [1].

All-trans retinal is needed for NpSRII to change it's conformation into an active light absorbing pigment. It can either be added to the growth media or produced by the organism. Phototactic stimuli can be delivered through a light pulse at 500 nm.

Design

De novo Synthesis by GeneArt.

Codon optimized.

Characterization

Receptor characterization

coming soon

Chemotaxis assay

Video 1: E. lemming in action.
The unprocessed microscope images are available here.

To observe chemotactic behaviour, cells were grown at 30 °C in Lysogeny Broth to on OD of 1.0. All-trans retinal has to be added to the media for NpSRII to change it's conformation into an active light absorbing pigment. The Archeal Receptor was subloned under the control of an IPTG inducible promoter. Phototactic stimuli were delivered through a light pulse at 500 nm and cells tracked.

The video shows the iGEM 2010 project of the ETH The E. lemming. The core idea was to control the swimming of E. coli cells by repressing or inducing tumbling by applying short blue light pulses. This movie shows a short sequence of the E. lemming as it changes its swimming behavior when sensing changes in the blue light signals. Please note that the natural adaptation system of E. coli downstream of the light receptor is active in this mutant, such that the swimming behavior only changes directly after the blue light is switched on or off, but is not necessarily different between long periods of light on or off. All cells but the E. lemming are visualized with a blue glowing. The E. lemming is glowing yellow, with its current movement direction visualized with a yellow light cone. The transfected E. coli cells were grown until a cell density of around 1.0 OD at 30 °C and imaged with a 20x light lense in a approximately 50 μm high flow channel. For more information please visit the ETH iGem 2010 team's wiki page at http://2010.igem.org/Team:ETHZ_Basel .

Angle change

Figure 1: Angles of the E. lemming in video 1.

The angle of the E. lemming during that measurement (see Video 1) as calculated from the central differences of its positions is depicted in figure 1. The estimated reaction times between the switching of the blue light and the reactions of the E. lemming are marked in the image. For the reaction delay between switch-on of the light and straight swimming, we obtained Δt₁≈2.1s and Δt₂≈3.0s. For the delay between the switch-off of the blue light and start of tumbling it was only possible to estimate the time delay for the second light pulse, Δt₃≈2.4s. White background: blue light off. Light blue background: blue light on.

References

[1] Jung, Spudich, Trivedi and Spudich: An archaeal photosignal-transducing module mediates phototaxis in Escherichia coli. Journal of bacteriology. 2001; 21.

Sequence and Features