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iGEM 2008

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Project Details


Completed Systems



Engineering multi-functional probiotic bacteria

Engineered gut flora

The human gut houses a diverse collection of microorganisms, with important implications for the health and welfare of the host. We aim to engineer a member of this microbial community to provide innovative medical treatments. Our work focuses on four main areas: (1) pathogen defense, either by expression of pathogen-specific bacteriophage or by targeted bursts of reactive oxygen species; (2) prevention of birth defects by folate over-expression and delivery; (3) treatment of lactose intolerance, by cleaving lactose to allow absorption in the large intestine; and (4) regulation of these three treatment functions to produce renewable subpopulations specialized for each function. Our research demonstrates that synthetic biology techniques can be used to modify naturally occurring microbial communities for applications in biomedicine and biotechnology.

Why engineer gut microbes?

The large intestine: an ideal bioreactor

The human digestive tract

The human intestinal track is a perfect environment for bacteria. It is a 37°C mobile incubator with a constant stream of food. While bacteria are present in all parts of the intestinal track downstream of the stomach, the majority of those bacteria reside in the large intestine. There are approximately 1012 bacterial per mL in the large intestinal lumen, comprised of between 500-1000 different species of bacteria. Of these species, approximately 30 species compose 99% of all bacteria in the large intestine. Estimating there is roughly 100 mL of feces in the large intestine, all the bacteria in our gut outnumber all the cells in the human body 100 to 1hooper.

Probiotic bacteria and other natural examples

Electron micrograph of Lactobacillus brevis, a probiotic lactic acid bacterium

Most of the bacteria in our gut have yet to be characterized because they are difficult to culture, owing to their sensitivity to oxygen. However, several species are known. Several bacterial laboratory strains are derived from the well-known Escherichia coli (a non-pathogenic type) which is normally present in the large intestine. Because of its use in research, E. coli is the most well characterized bacteria to date. Another bacteria, Bacteroides fragilis, plays an important role in proper development of the immune system and in controlling intestinal inflammation. Specifically, B. fragilis produces a starch called polysacharride A. In mice that had been raised in a sterile environment since birth (the intestinal track is initially sterile at birth and requires outside sources of bacteria to populate it), the immune system had less than normal levels of CD4+ killer T cells, a necessary white blood cell to battle infections. However the CD4+ levels returned to normal when the mice were raised again in a sterile environment, except for the presence of B. fragilis. Polysaccharide A alone, not the mere presence of Bacteroides fragilis, was responsible for the improvement, since mice raised with B. fragilis that could not produce polysaccharide A showed the same levels of CD4+ cell as the sterile micemazmanian.

Nissle 1917: Probiotic, commercially available E. coli

Mutaflor - a commercially available preparation of Nissle 1917

Talk about Nissle 1917

For more details, please see our project page.


  1. hooper pmid=12055347
  2. mazmanian pmid=16009137


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