Team:WHU-China/Description
In this part, we mainly explain the design related to the biological part. This year we want to use the Ark to recover the phosphorus. The part of the bio device responsible for recycling the element (phosphorus) is called the bio-conveyor.
This conveyor can carry our engineering bacteria for the recovery of phosphorus. The conveyor belt will carry our engineering bacteria in different environments, and express different proteins in different environments to specifically recover the phosphorus in the environment. The conveyor belt mainly includes two biological pathways, one is the construction of the conveyor belt (the symbiosis of the bacteria and algae), and the other is the phosphorus recovery system of the conveyor belt (the circulation control pathway).
The construction of the conveyor is not an easy thing! In addition to the most critical energy input problem，to some extent, our engineered bacteria are directly exposed to threats from environmental pollutants, and it is necessary to confer bacterial resistance. Moreover, the phosphorus-concentrating efficiency of engineering bacteria is also affected by many environmental factors. If there is no stable environment, the whole system will be greatly affected, so it is unreliable to fix the bacteria directly on the conveyor matrix.
After several HP and brainstorming and extensive literature review, we decided to use synthetic biology to build multi-biological systems. Through literature search, algae and bacteria have good phase, algae can provide engineering bacteria energy through photosynthesis, and The extracellular matrix EPS of algae can confer excellent environmental resistance to bacteria, and the growth state of the bacteria is also stable in the symbiotic system of bacteria and algae.
Finally, considering the characteristics of the conveyor, we have adopted a more advanced method of symbiotic biofilm formation, which is to compress the suspended symbiotic liquid into a biofilm, which can carry out the subsequent phosphorus accumulation more efficiently. However, the establishment of biofilms will encounter the disintegration problem caused by the low stability of the membrane on the traditional filtration method. We explore the more efficient membrane formation method and use synthetic biology to make the engineering bacteria Express tighter proteins that bind to algae to enhance biofilm stability!
We have tried a total of three methods, these simple pathways can theoretically greatly enhance the stability of the membrane.
Frist Lectin Lectin is a protein derived from green algae. It can be combined with a large amount of negatively charged extracellular matrix EPS of algae because of its electrical characteristics. We express it by membrane display.
Second Cbd Cbd can bind to the cell wall of algae
Third FimH—lectin The expression of lectin on the bacterial pili is based on the idea of Imperial College of Science and Technology for 17 years. The pili is spread throughout the body of E. coli. It is theoretically very effective to express lectin at the end of the pili to make it more fully integrated with algae.
2. Phosphorus recovery system (circulation control path)
The conveyor is the technical core of the Ark, and this phosphorus recovery system is the core of the conveyor belt.！The specific capture and recovery of the whole set of phosphorus is the function of this system. Our conveyor belts carry our bacteria in different environments. To achieve the specificity of their recovery, bacteria must express different proteins under different conditions. These proteins can control the accumulation and release of phosphorus in engineered bacteria. In short, the role of the circulation control pathway is to allow the bacteria to express two different proteins under different conditions and to cycle back and forth like day and night. This pathway is the essence of the biotransport, which can be subdivided into two parts, the functional part and control section
2. Control section
The above process PPK and PPN/X expression need to be repeated alternately, because the effects of PPK and PPN/X are diametrically opposite, so the control part must ensure that only PPK is expressed in the water environment without expressing PPN/X, and vice versa. . How to control the expression of specific proteins in a specific environment is a key issue - chemical small molecules such as iptg or other means can specifically express bacteria in a specific environment, but our expression is "circular "This means that the expression of each round cannot affect the expression of the next round. The chemical must consider the accumulated problems. Maybe after several rounds, the system will collapse, such as the accumulation of iptg to a certain extent. The PPK could not be closed inside the Ark and the recycling system crashed. In the end we chose - the lightest and most loop-friendly way to switch, we drew on the toggle switch and simplified and improved it in our system to design this path:
Ccas and ccar are light-sensitive and acceptor proteins that, when they receive a light signal (green light), activate the cpcg promoter and turn on downstream expression. If the red light signal is received, the activation of the cpcg promoter is removed and the downstream expression is turned off.
The Ccasr system is a classic light control system. We use its system to combine with the non-gate to achieve specific control functions in our path.
Because the conveyor belt runs very slowly, the expressed protein and non-gate control signals will be degraded after they stop expressing, and the light promoter will not leave any traces. Therefore, in theory, this loop control channel can continue to work. See the modeling section.
