Team:St Andrews/project/objectives

Project Description

The Problem: Cholera

Cholera (V. cholerae) infects 5 million people per year, worldwide and can kill within hours if left untreated. Like all diarrheal diseases, cholera is particularly deadly in children.

Whilst the standard treatment for cholera is some combination of fluids and antibiotics, there is no cure. Efforts have been made towards an effective cholera vaccine, but as yet this has been unsuccessful.

We believe that prevention is better than cure and to stop cholera from causing severe illness and potential death. Our aim is to investigate whether the basic science behind preventing cholera could work.

Quorum Sensing in Vibrio cholerae

Most cholera cells are killed off by stomach acid, but those that remain alive attach to the gut wall and multiply. At this low cell density, autoinducer concentration is low, and virulence factors are expressed. Once high cell density is reached, enough toxin is present to cause severe diarrhoea. At this point, the autoinducer concentration is high, and virulence factors are repressed. The now avirulent Vibrio cholerae detach from the gut wall and are flushed out of the body to infect a new host. Our idea is to synthesise Escherichia coli bacteria that will use this ingenious mechanism to communicate with Vibrio cholerae. Our engineered Escherichia coli will harmlessly colonise the gut, and in large numbers secrete the cholera autoinducer, CAI-1. This will cause an immediate high autoinducer concentration to be detected by incoming Vibrio cholerae cells which then become avirulent and harmlessly pass out of the body.

The Plan

Biology Lab Work

(1) Adding new functionality to the signalling parts present in the registry by re-engineering the existing LuxR quorum sensing system to create a bistable switch. This will allow us to infer a signalling molecule concentration required to deactivate the system much lower than the concentration required to activate it. We will characterise this system by using a fluorescent protein reporter and measuring fluorescence at different cell densities.

(2) Adding the cholera autoinducer synthase gene CqsA to Escherichia coli so that CAI-1 is secreted. The eventual aim is that the bistable switching system will be used to control CqsA expression, so that the ability to compete with other bacteria in the human gut is not compromised by this metabolic burden.

Modelling'

Generating ordinary differential equations to model quorum sensing in V. cholerae and on modelling more complex problems such as bistability and multiple quorum loops working in tandem of our parts.