iGEM Toulouse 2015



Treating Varroa destructor

After being attracted, varroas will have to be eliminated. Beekeepers already use some treatments to fight against varroa, like oxalate, fluvalinate, thymol or formate. All these treatments use high doses which are toxic for bees and humans. Beside, varroa is developing resistance against some of these treatments, making them ineffective [1].

In the list of the molecules mentioned above, formate has already prove its acaricide property [2], and to our knowledge, no resistance has been reported yet. Formate also presents the advantage to be naturally synthesized by E. coli therefore is a natural molecule.

Here, the project main goal will be to synthesize formate at the lowest concentration allowing an efficient elimination of varroa in the trap. The bacteria will produce formate during a defined period, in order to reduce doses and minimize the toxicity on bees.

Formate acaricide activity test

Before formate production by our strain, it was necessary to check the "miticide" activity of the molecule with a specific test. In this experiment, three varroas were placed in a Petri dish containing a cotton soaked with 400 µL of formate at different concentrations (50µM, 500µM, 1mM et 10mM).

The experiment ran for 6h and the varroas’ death was validated when no movement were detected even after a stimulus. The mite observation was performed with a binocular magnifier.

Figure 1: Formate miticide activity test

How to synthesize formate with E. coli?

Formate is a simple organic acid that can be produced with E. coli. The initial substrate, glucose, is decomposed into pyruvate during glycolysis, and formate is naturally synthesized by two key genes:

  • pflB (Accession Number: EG10701) encoding the pyruvate formate lyase which catalyzes the cleavage of pyruvate into C1 and C2. This enzyme is sensitive to oxygen and is only active in microaerobic or anaerobic conditions, which is the case within our device [3].
  • pflA (Accession Number: EG10028) encoding the pyruvate formate lyase activase, which is directly linked with the pyruvate formate lyase, enabling its activation [4].

Figure 2: Enzymatic reaction of the formate synthesis

The key genes for formate synthesis were over-expressed. The genetic construction (here) was done by assembling the abovementioned genes, placed under the control of the P(Bla) constitutive promotor (BBa_I14018). RBS (BBa_B0030) were inserted to allow protein expression, and a strong terminator ended up the construction (BBa_B1006).

Figure3: Formate pathway



  • [1] Elzen PJ, Baxter JR, Spivak M & Wilson WT (2000) Control of Varroa jacobsoni Oud. resistant to fluvalinate and amitraz using coumaphos. Apidologie 31: 5
  • [2]Satta A, Floris I, Eguaras M, Cabras P, Garau VL & Melis M (2005) Formic acid-based treatments for control of Varroa destructor in a Mediterranean area. J. Econ. Entomol. 98: 267–273
  • [3] Becker A, Fritz-Wolf K, Kabsch W, Knappe J, Schultz S & Volker Wagner AF (1999) Structure and mechanism of the glycyl radical enzyme pyruvate formate-lyase. Nat. Struct. Biol. 6: 969–975
  • [4] Crain AV & Broderick JB (2014) Pyruvate formate-lyase and its activation by pyruvate formate-lyase activating enzyme. J. Biol. Chem. 289: 5723–5729