Signaling molecule OHHL

Figure 1. N-3-oxo-hexanoyl-L-homoserine lactone

N-3-Oxo-Hexanoyl-l-Homoserine Lactone belongs to the family of Acylated Homoserine Lactones (AHL). In our project , we use the LuxI-LuxR quorum sensing system to drive the signal from the sender to the receiver cells. The LuxI sender construct produces OHHL. The OHHL diffuses in the agar to reach the receiver cells containing LuxR which in turn triggers the hydrolase expression in the receiver colonies. The receiver cells comprise promoters that are tuned to express specific hydrolases depending on the amount of incoming OHHL. The OHHL diffusion is very important in that it drives the enzyme (hydrolase) expression in the non-mines depending on different high pass filters. The OHHL concentration processed by the receiver cells depends on the number of mine colonies. Through an enzyme-susbtrate reaction that generates a colored product the player obtains information about the number of mines surrounding a non-mine.

Diffusion tests of OHHL

Figure 2.1: Scanned image of GFP Fluorescence of OHHL Diffusion with GFP receiver cells with two senders

In our biological circuit design, the diffusion of OHHL from the sender to the receiver is vital in order to express the different orthogonal hydrolases. This is because the hydrolases are expressed under the control of plux promoters which are induced by OHHL.
In order to visualize the OHHL diffusion, experiments were carried out, using GFP as reporter. We started with using the part [http://parts.igem.org/Part:BBa_J09855 BBa_J09855] cloned with GFP as our receiver. We tested the sender with part [http://parts.igem.org/Part:BBa_K805016 BBa_K805016] under a constitutive promoter. double-layer agar tests (See protocol) were performed with the GFP receiver cells spread evenly as a top layer agar, and the 1.5 μl sender cells as source of signal OHHL. The diffusion pattern was measured over 12 hours with an fluorescence imager (Kodak Image Station 4000mm) and pictures were processed with molecular imaging software. The distance of diffusion was noted as 1.5 cm as the radial diffusion distance across the sender colony. The time and distance data from these experiments were used for the spatio-temporal model of the OHHL diffusion.

Figure 2.2: Scanned image of GFP fluorescence of OHHL Diffusion test to check diffusion time and distance

Figure 2.3: ImageJ analysis of fluorescence peak showing radial diffusion around one sender colony

The image to the left shows the GFP fluorescence in a double layer agar experiment after 11 hours. In order to quantify the time and distance of diffusion of OHHL from the sender to the GFP receiver, we analyzed the scanned image of the plate with the image processing program ImageJ . The analysis from ImageJ is shown in the picture to the right. The picture shows the GFP fluorescence in gray scale with distance in inches. The distance of diffusion can be seen as 1,2 inches, that is nearly 3 cm. Hence, for the further experiments, the colonies were placed apart from each other at a distance of 1,5 cm in a hexagonal manner.

We thank our sponsors: