Revision as of 01:03, 27 October 2012 by Suxiaohui (Talk | contribs)

The Lyon-INSA iGEM 2012 solution: “Biofilm Killer”

Biological solutions presented previously are very interesting and promising. But synthetic biology could make them even more powerful by providing a technology:

  • able to control, prevent and protect industrial equipment;
  • using non-persistent molecules in the environment;
  • minimizing harm to individual, products and environment.

To meet these challenges, we have chosen to build a bacterial strain based on the environmental friendly Bacillus subtilis strain (already used to feed animals and promote healthy vegetable growth. “Biofilm Killer” was engineered to both destroy and then replace, if needed, the deleterious contamination by a positive biofilm.
Our solution is based on 3 genetic modules:

    • KILL and SCATTER the biofilm. The effect of the biocide and scattering agents produced by the bacteria can be enhanced by the “torpedo” behavior of the Bacillus swimmers;
    • COAT the surface with a surfactant reagent in presence of the inducteur 1 (xylose);
    • STICK to install a positif biofilm in presence of the inducteur 2 (IPTG).

Estimating the cost of the current industrial solutions

In order to compare our biological solution to the currently used ones, we first approached companies whose concerns were similar to ours : they kindly gave us some of their data related to the price of their sterilizing solution.

A first company that accepted to answer our questions estimated that, considering the use of chemical reagents (€50 per use : 3 kg of cleaning products, €15 of disinfectants) and of a sterilizing filter to recover biological waste (€100 to €300 per use depending on its size), the total cost of a 4-hour wash of a 1000L tank was from €165 to €365 ($215 to $475) per sterilization.

The second one indicated a €480 ($625) cost estimation for a 1500L tank per sterilization.

Such estimations made us confident on the competitive potential of our bacteria, considering the low cost of their growth.

Biofilm Killer implementation : a viable solution

We extrapolated both our results in 96-well microplates, which showed us the optimal effective concentration of cells for a given surface (2.5x108 cells for a growth area of 0.34 cm² covered by S. aureus), and the market prices for genetically modified Bacillus subtilis freeze-dryed cells to an industrial facility model (1000L tank plus 20m of pipes). We used two different prices in our calculations: the average price ($5.55 / kg) and the highest price ($9.58 / kg).
In the end, we estimated that the bacterial cost of the sterilization of our model 1000L facility would be $0.3 per use in the first case and $0.5 per use in the second one. However, to confine the biological waste, we would also need a double 0.45/ 0.2 µm filter, so that the global price would be increased by at least $100. We also developped a sterilization protocol for this tank (see below) :

Besides, we generalized our biological prices in relation to a 1 m2 surface to sterilize : it would then be $0.06 / m2 for the average price and $0.1 / m2 for the highest one.
"Biofilm Killer" could be conditioned in 25kg bags of freeze-dried cells (usual conditioning in the market) and proposed to sale at an attractive price (estimated $12.25, FOB price).

Main advantages

Lower cost : No need to have a protein purification step which is very expensive.
Eco-friendly: “Biofilm Killer” won’t release toxic chemicals in the environment since the proteins used can be easily destroyed.
The “biological swiss-knife”: “Biofilm Killer” should be able to replace mechanical cleaning actions thanks to the swarming properties of our strain which can penetrate deep inside the biofilm and release the active molecules in situ all over the biofilm.