Modeling Do One Thing & Do It Well.
Design
Device 1.0
In order to enable our project to be applied in real environment, we designed and made Device 1.0. Because the productivity of attracting substance by E.coli is limited and the price of man-made attracting substance is quite high. We choose low-cost CO2 as our assistant attracting substance since it was demonstrated that carbon dioxide has a function of attracting nematodes[1-3].
Our device has four areas. The first area is CO2 generating area. We produce CO2 by mixing limestone and dilute hydrochloric acid together, which is widely used in industry. The second area is E.coli culturing area. It includes a medium inside the device - to culture modified engineering bacteria. The third area is light controlling area, which includes a LED light. When it is turned on, red emission will activate the promoter and bacterial cells will express attracting substance; while the LED light is turned off, toxalbumin will be produced. The fourth area is made up of a cuboid outer shell, which can support the device.
The figure above shows our product – Device 1.0. We have simulated our device in the lab and our results show that our system is able to work under real-world conditions.
There are 8 steps to apply our device in farmland as shown in the video above. And the procedures below were conducted in a fume hood.
- Step 1. We gathered a box of soil from our farmland.
- Step 2. We applied culture medium onto slide glasses.
- Step 3. We gathered several small stones used as CaCO3 and put them into the test tube.
- Step 4. We added HCl into the separating funnel.
- Step 5. We opened the faucet of the separating funnel in order to let HCl flow into the test tube under the atmospheric pressure. Then small stones reacted with HCl to liberate CO2. We also demonstrated how to use red LED light in the video.
- Step 6. We put the device into the soil.
- Step 7. After 3 hours of incubation, we took out the device and removed the slide glasses.
- Step 8. Finally, we tested the results using a microscope. In the video, we showed the movement of a nematode that we separated from soil from Hebei Province, China.
Device 2.0
After discussion among team members about device 1.0, we found several deficiencies. First of all, the size of our device is so limited that the reaction substrate (limestone and diluted hydrochloric acid) is not enough to generate CO2 constantly. Replenishing the reaction substrate frequently will greatly increase the cost. Secondly, the space utilization percentage is low on the slide medium; as a result, the production of both attractant and toxalbumin is low. Lastly, LED tube is sizable and needed to be powered constantly, thus not suitable for farmland. In device 2.0, we improved device 1.0 in those three aspects mentioned above. Indeed, we need to further improve our device.
Firstly, we assume that engineering bacteria can produce ideal concentration of attractant and toxalbumin (the ideal concentration is in reasonable range). Then, considering the problem of space utilization rate and the fact that E.coli can only grow on the surface of the medium, we changed the medium’s shape to sphericity to reach the highest space utilization percentage. Meanwhile, our device has been shaped to sphericity too, and the LED light has been moved to the center so that the whole surface can get the radiation evenly. A design like this enable us to use mini LED light bulb, and use solar energy instead of electricity as our power resource. This change fulfills our aim to save money and energy, which is also more economical and enviromentally friendly.
As shown above, device 2.0 has two shells – an outer shell and an inner shell. There are tiny holes on the outer shell, which allow nematodes to enter the device. The holes are biosynthetically designed to prevent other soil organisms from entering. The red LED light can be supplied with the power from solar power pane, which will be put on the surface of the farmland. And we can achieve remote control by using radio technology.