Our goal is to create a solution against hives infestation by varroas. In order to get the best out of ApiColi in the treatment of varroosis, we designed a trap named TrApiColi. TrApiColi was thought up to take into account ethical reflection, safety and ease of use for beekeepers.
Since the switch between the production of the two molecules is regulated by light, our bacteria need to be outside of the beehive. Thus, the trap was designed to be placed at the entrance of the hive, in order to act before infection and try to prevent the entry of as many mites as possible.
The four different parts of our trap
TrApiColi is composed of four main parts:
1. A grid lined up with the bottom board
The bees usually enter the hive by landing on the bottom board before walking inside. Because of the alignment of the trap with the board, it will not disturb the bees' comings and goings. The holes are big enough to let the varroas fall through them, but not the bees.
2. A funnel, to channel all the falling varroas
The grid and the funnel
3. A transparent collector, containing the bacteria confined in a special bag
It is designed like a fish bottle trap: the tube from the funnel goes on for a few centimeters inside the collector to ease the entry of the varroas in the collector while preventing them from exiting. The special bag is described in the "ApiColi containment and culture" part below.
4. A roof, to protect the trap from the rain
Associated with pannels blocking the sides of the entrance, it forces the bees to walk on the grid. This channeling does not disturbs the bees.
The dimensions of the trap allow it to adapt to almost every beehive. Indeed, most of the hive types have the exact same entrance. Thanks to that, the trap can be easily and perfectly installed on the hive by the beekeepers without drilling or cutting.
The trap was designed using Catia and then 3D printed in order to build a prototype. It is used as a demonstration device for the beekeepers and the general public. This trap could not be tested without coating because the porous plastic used for 3D printing is permeable to liquids and gases. Moreover, the modeling showed that this version of the trap is yet to be optimized to ensure a proper diffusion of our molecules, see more in "Modeling" part.
The 3D printer used to construct our trap and the result of 3D printing: TrApiColi
ApiColi containment and culture
The use of genetically modified organisms in a field associated with edible products requires to carefully consider the issues of safety, national legislation, and public opinion. In this context, we looked for a solution that would isolate our engineered bacteria from the environment, while still allowing its growth and gas diffusion.
We found the solution in the iGEM Groeningen 2012 project that used a special polymer called TPX® in order to keep their bacteria from contaminating meat, their edible product.
TPX® is composed of Polymethylpentene, a porous polymer, and is commercialized by the company MitsuiChemicals (4-methylpentene-1 based polyolefin, Mitsui Chemicals, Inc.). In order to perform our experiments, we contacted MitsuiChemicals who offered us some samples of TPX®.
A TPX containing 6 ml of LB medium
As in the Groeningen 2012 project, our bacteria need to be separated from the growth medium until the beekeeper decides to use the trap. In order to do that, freeze-dryed bacteria are contained in a small polyvynil chloride bag placed inside a bigger TPX® bag. Since polyvynil chlorid is fragile, the user have to break it in order to start the growth.
To check the feasability and safety of our device, several tests have been performed:
- Growth tests in TPX®: Culture of the strain E. coli BW25113 in a TPX® bag (ie. in microaerobic conditions, without agitation and miming batch culture condition), as it would be in the field
- Gas diffusion tests: Permeability of butyric acid and formic acid through the TPX® bag
- Safety test: Impermeability of the bag of TPX® to the bacteria
- Bacterial survival over 15 days in microaerobic conditions
- Carbone source test: choice of a carbon source to produce acids during at least 10 days
- Acid toxicity on E. coli