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Revision as of 15:55, 6 August 2013
Overview
As we all know, the role of biotechnology have been more and more important in modern manufacturing. Fermentor, as the important tools in biomanufacture, should be considered as a complex rather than a simple machine. In fact, the heat produced by microorganism in fermentor will cause a large consumption of energy. By the way, the maximum of microorganism density is not always the best for production efficiency. Under this circumstance, to improve the ability of engineering bacteria to resist hot environment and to control their density in an appropriate area is necessary. Let’s set E.Coli as an example
Here, in figure A, we can see the normal condition: there’re a lot of E.Coli working, but it’s not crowded, and the temperature is perfect.
But there will be more and more E.Coli! The temperature goes up with the density. With the temperature higher and higher, all the E.Coli are in danger! They feel like live in fire. We could, just as what we do before, use our machine to put up the “fire”, which, as I said before, will consume a lot of energy. But what if the E.Coli get organized, and put out the fire by sacrificing a small part of them, leave nutrition to the others?
That is just what we want, like picture B, E.Coli get together to fight with fire, so that they can survive in a hotter environment. But the temperature is sill going up with density. Too crowded! There must be a way to decrease the density and to cool down the fermentor! As the disaster draws near, the saviors show up. When the temperature reaches the “red alarm” level, some brave E.Coli will sacrifice themselves to decrease the density up to an appropriate number. With the decreasing of density, less heat is generated, the fermentor return back to a cool condition. The sacrifice of those E.coli contributes to the production efficiency, just like the dead encourage the live.
How to “lead” the E.Coli fight with heat?
There is a protein family called HSP. They can help cells to fix the damage caused by heat by restoring the protein back to normal condition. In our design, HSP are controlled by a kind of RNA switch. Once the temperature reaches the level we set, the switch will open automatically. That is the weapon we give to E.Coli to fight with heat. This device is our forth device.
How can the E.coli sacrifice themselves?
Maybe many people think bacteria are selfish creatures, but that is not totally true. MazEF, is a widely used system among wide bacteria. With this system, many bacteria will sacrifice themselves, and leave nutrition to the left ones when facing threats from dangerous environment, such as heat, lack of food and so on. MazF , which has RNA cleavage activity, is a kind of toxin. MazE, on the other hand, is the antidote of MazF. When MazE can combine with MazF, the cell will not be harmed. But once we inhibit the production of MazE, the cell step into programmed cell death(PCD). In our design, we add our MazEF into E.Coli, so once the pathway was open, E.Coli will be ready for sacrifice. That is our third device
How can you ensure the “sacrifice” will not become group suicide? In other words, how can you control the number of E.coli who sacrifice?
Actually our inhibition on the production of MazE will not last long. We set a oscillating pathway to control the inhibition to ensure the MazE is much enough to keep most E.Coli in a normal condition. The inhibition will be intermittent, not continuous. That is our second device. The simple description is A inhibit B, B inhibit C, and C inhibit A, they become a cycle.
How can E.Coli know it is time to sacrifice?In other words, what contribute to the open of whole pathway?
The whole pathway begin from AHL, which is linear connected to the cell density. The AHL will combine with a protein called LuxR, and form a complex. When the complex reaches a level, it will activate the intermittent pathway, which is the second device. This AHL part is our first device, the beginning of our whole pathway.
Our design is a self-control system. It not only enlarge the temperature tolerance maximum, but also set a limit on density and released heat, so that the manufacture progress can be kept on the best condition. The idea can not only decrease the consumption of energy, but also bring an evolution of bio-manufacture industry. In a word, although our work is far from perfect, but it provide a possibility of automatic style for the whole ferment industry.
