Background:

Recent studies have evidenced that the intestinal microflora can actually be considered an organ of the body. It has several functions in the human gut, mostly metabolic and immunologic, and it constantly interacts with the intestinal mucosa in a delicate equilibrium. It is therefore believed that having a beneficial and healthy intestinal microflora is very important for human health.

Project:

Our aim is to modify a bacteria normally found in human gut and create a safe, controllable and versatile molecular platform which can be used to produce a wide range of molecules (as for example other antibodies or enzymes) leading to a beneficial probiotic.

For this purpose we have chosen the E. coli strain Nissle 1917 which has been used for many years as a probiotic. We designed a robust gene guard system regulated by a novel and easy to control inducible switch that activates the production of a human antimicrobial peptide that can kill the bacteria and also avoid horizontal transfer.

Our gene guard system is based on the cumate molecule present in the common spice: cumin. In absence of this molecule our system produces a repressor (CymR) which inhibits the expression of an antimicrobial peptide. When administered and therefore present in human intestine, cumin recognizes and disables the CymR repressor resulting in the production of the antimicrobial peptide cathelicidin LL-37 which causes bacterial death. In case of plasmid transfer into other bacteria of the plasmid carrying the expression system, the expression of the antimicrobial peptide will be activated immediately because the receiving bacteria do not produce the CymR repressor needed to repress the expression of the antimicrobial peptide.

Application:

The safe probiotic constructed here can be used to produce nutritious, preventive or therapeutic molecules. For example, we have used it to produce an antibody against the emerging virus called Norovirus; this virus which has a dramatic spreading speed: rates of reported Norovirus outbreaks reach 21 million cases of acute gastroenteritis per year, 70.000 of those need hospitalization and 800 die.