Testing chassis survival in sugar water
The final BeeT product will be applied using sugar water, which is transported into the hive by worker bees. This means that our chassis needs to be able to survive in a nutrient limited environment, which does have a high sucrose content. In order to test this, we simulated a sugar water environment and tested whether bacteria can survive it. The result of this was that our chassis bacteria, Escherichia coli , was able to survive up to at least an entire day in the sugar water. This means that the bees will have at least 24 hours to pick up some of our BeeT.
The modeling results from the metabolic modeling project only showed what would happen in the time period of 90 seconds to 90 minutes after being put in the sugar water. Because of this, more evidence was needed to see what would happen to the E. coli in the sugar water for the time scales we are interested in. We know the presence of the high amount of sugar water leads to osmotic stress.1 This is because the sucrose molecules from the medium are not able to travel across the cell-membrane, but still pull the water molecules present inside the cell towards them. The effects of the osmotic stress on the bacterium were not clear outside of the 90 minute range determined by the metabolic model. However, as determined by the BEEHAVE model, we require that the BeeT survives for days in the sugar water. In this project we aimed to experimentally determine how long BeeT can survive in osmotically unfavourable conditions.
The results from the experiments were a great success, as you can see in Figure 1 and 2. The result of experiment 3 is that the E. coli was still able in the LB was still possible after the 24 hours in the sugar water solution.
All three experiments clearly show that sugar water is not as lethal as first hypothesized. Not only that, but the results fit with the model hypothesis in that long-term survival is indeed possible. Thus we have shown that E. coli can indeed be used as a chassis for our BeeT. This result was taken into account in the BEEHAVE model.
Method of testing
The method used to test the survival of E. coli in sugar water is a simple growth experiment. First, the bacteria grow overnight in LB medium. Then, 5 µL per sample of this is pipetted into various concentrations of sterile sugar water made of varying amounts of sucrose, ranging from 0 g/L up to 625 g/L, and sterilized tap water. We then took 5 µL samples of the sugar water and inoculated them into fresh 200µL LB medium wells and left to grow overnight.