Team:IIT Madras

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The Problem

Our iGEM project aims to tackle the emerging problem of antibiotic resistance by leveraging the power of natural selection under selective pressure. It is known that higher exposure to antibiotics leads to the resistance against that antibiotic in bacterial populations.

Anti microbial peptides are small protein molecules that have been shown to have anti-microbial activity. They are also also known to exhibit lower tendency to develop antibiotic resistance. Recently, However, it has also been reported that a prolonged exposure to anti-microbial peptides could also lead to the emergence of resistance in bacteria

Our Solution

Here, we come up with a solution to this problem. We will synthesize a bacterial system that:

1. Senses the cell density of pathogenic bacteria
2. Our system releases anti-microbial peptides which kill pathogens, when it has sensed high cell density
3. As the population goes down we release a peptide that neutralizes the activity of anti-microbial peptides, resulting into a stress free environment.The stress-free environment would be favourable to the wild type compared to the mutants which have developed antibiotic resistance

Most pathogenic microbes secrete quorum sensing (QS) molecules like AHL, AI-2 when present in high cell density. QS molecules are sensed by receptor proteins on the cell surface of pathogens. These signaling molecules help them in regulating their communal activities.

In the lab, we will be using E.Coli DH5alpha strain as pathogenic model. DH5alpha does not secrete quorum sensing molecules natively. Therefore, we will genetically modify E. coli DH5alpha strain to release Auto-Inducer-2, a signaling molecule.[Ref. 4] We do this so as to create a recombinant that mimics many pathogenic bacterium that secrete quorum sensing molecules.

We will be using Lactococcus lactis MG1363 strain as a receiver. It has a simple circuit to detect high and low cell density of pathogens and release the appropriate molecules. L. lactis activates the expression of Alyteserin (antu-microbial peptide) at high cell density and NAly (neutralizing anit-microbila peptide) at low cell density. The precise mechanism with the genes involved is explained below.

At low cell density, luxP,luxQ,luxU receptor proteins act as kinases that results in the phosphorylation of luxO (luxO-P) that activates qrr1-5 sRNAs with the help of sigma54 RNAP subunit factor, qrr RNAs degrade the mRNA of LuxR which has been found to activate and repress a number of gene when expressed in the cell.[Ref. 3]

While at high cell density, the same receptor proteins (LuxP,Q,U) acts as phosphatases which removes the phosphate from LuxO-P and this results into the higher expression of LuxR gene.[Ref. 3]

Through this project, we aim to investigate a few questions and hypothesis:

1. Is bacterial resistance a big cause of concern when using antimicrobial peptides?
2. Are oscillations in cell population observed when our system is used? Are the oscillations damped?
3. How effective is the activity of NAly in neutralising the effects of Alyteserin?