Team:CityU HK/Description

Description - City University of Hong Kong 2015

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Overview

What is lactose intolerance and 
Why we would like to tackle it
For most people, indulging in sweet food like ice-cream, cheesecake and chocolate is as natural as breathing. However, the same kind of food could remind some people of the discomfort and annoyance brought on by lactose intolerance. Should they avoid all these delicacies altogether or resort to taking lactase pills every time after eating food containing lactose? Here, we offer you a new choice.  
Lactose intolerance is a gastrointestinal problem signified by symptoms such as bloating, stomach cramps, diarrhea and nausea after consuming milk or dairy products. Normally, lactase in the small intestine will break down lactose into glucose and galactose for absorption. For people with lactose intolerance, their body produces little or no lactase. Undigested lactose will therefore enter the colon where bacteria may ferment the lactose to produce lactic acid and gases as by-products. These by-products are the culprits of the symptoms.
There is evidence suggesting that dairy consumption is associated with lower risk of hypertension and higher rate of bone mineralization. To help people with lactose intolerance to enjoy the diverse health benefits from dairy consumption,  our iGEM Team (CityU_HK) has set a goal to tackle this problem. 

How we are going to tackle it
We aim to design and construct a probiotic E. coli strain that (1) produces high level of the beta-galactosidase enzyme (a type of lactase) constitutively, and (2) autolyses to release the beta-galactosidase enzyme upon detecting lactose in the external environment. For process (1), we will construct a lacZ (beta-galactosidase)  -lacY (lactose permease) biobrick that is driven by a strong constitutive promoter  to enable high  expression of the beta-galactosidase enzyme. For process (2), we will construct a lysis cassette  consisting of the S (holin)-R (endolysin) -Rz (spannin) genes driven by a lacI promoter  to facilitate lactose-induced cell lysis.

To optimize the efficiency of E. coli cell lysis, we will carry out the following modifications to certain genes in the lysis cassette:
     1. Genes in the lysis cassette  will be codon optimized for optimal expression in E. coli;
     2. The anti-holin component will be deleted to speed up cell lysis;
     3. Specific mutations will be introduced into the lysis gene cassette to facilitate shorter lysis time.

In this project, we will also prepare and compare the lysis efficiency of two different lysis cassettes – (1) Cassette 1 will be constructed using the Sλ, Rλ and Rzλ genes derived from E. coli lambda phage, and (2) Cassette 2 will be constructed using the S21, R21 and Rz21 genes derived from E. coli phage 21.