Eco-friendly E. coli

Introduction

Our Bee. coli can express antimicrobial peptides such as defensin and abaecin to fight against Nosema cerenae. However, it is also possible that our Bee. coli can contaminate the natural environment and cause death to other species. Therefore, a light-induced lysis system was created to ensure our Bee. coli only lives inside of the bee.

Background

Blue Light Sensing Device

We chose to use [http://parts.igem.org/Part:BBa_K592016 K592016] and [http://parts.igem.org/Part:BBa_K592006 K592006] as our light sensing device. [http://parts.igem.org/Part:BBa_K592016 K592016] consists two parts: YF1 and FixJ. YF1 is a blue-light sensor protein. It works in conjunction with its response regulator, FixJ. [http://parts.igem.org/Part:BBa_K592006 K592006] is a light-sensing promoter, which can express downstream gene when unphosphorylated FixJ presents. When exposed to blue-light, YF1 will be activated and phosphorylate FixJ. Phosphorylated FixJ cannot activate the light-sensing promoter [http://parts.igem.org/Part:BBa_K592006 K592006], and the expression of downstream gene will be repressed. This picture can simply show the logic of this light-sensing device.

Blue sensing device

Self-destruction Device

The self-destruction device is composed of blue-light sensing promoter [http://parts.igem.org/Part:BBa_K592006 K592006], the blue-light sensing protein [http://parts.igem.org/Part:BBa_K592016 K592016], and a set of genes from [http://en.wikipedia.org/wiki/Toxin-antitoxin_system toxin-antitoxin system]. The toxin gene will be constitutively expressed. Antitoxin gene will be placed after [http://parts.igem.org/Part:BBa_K592006 K592006]. When toxin and antitoxin genes are both expressed, antitoxin can repress the function of toxin and the bacteria can survive. However, when toxin gene is dominating, it will kill the bacteria.

Self-destruction device

Circuit design and Experimental Method

Circuit Design

[http://parts.igem.org/Part:BBa_K592016 K592016] is cloned after the constitutive promoter [http://parts.igem.org/Part:BBa_J23102 J23102], so the proteins YF1 and FixJ were continuing produced. Toxin gene is also cloned after [http://parts.igem.org/Part:BBa_J23102 J23102] and will be constitutively produced. When not exposed to blue light, the inactive YF1 will not phosphorylate FixJ, and the unphosphorylated FixJ can induce the downstream gene of promoter [http://parts.igem.org/Part:BBa_K592006 K592006], in this case, which is the antitoxin gene. When not exposed to blue-light, antitoxin can be expressed and consequently repress the function of toxin. When exposed to blue-light, the expression of antitoxin will be repressed, and constitutively produced toxin will kill Bee. coli.

Without exposed to blue-light, Bee. coli survives

Exposed to blue-light, Bee. coli will be killed

Experimental Method

First, we substitute antitoxin with green fluorescent protein [http://parts.igem.org/Part:BBa_E0040 E0040] and replace toxin with red fluorescent protein [http://parts.igem.org/wiki/index.php?title=Part:BBa_E1010 E1010]. By calculating the ratio of GFP and RFP, we can derive the expression ratio of toxin and antitoxin.

Testing Circuit

Next, by comparing the number of colonies of the plate that is exposed to light and the plate that is blocked from light after 16 hours of incubation, we can characterize the functions of our device.

Left: Light is blocked by aluminum foil.

Right: Plate is exposed to light.

This is the actual device we used to conduct this experiment.

This device consists of two sets of blue-light LEDs