Update background.md

docs/project/background.md

@@ -67,6 +67,12 @@ The key to this system is linking the activity of the biomolecule to the express
 
 To make this a self-sustaining evolution system, a few more adjustments are needed. We provide the phages with a steady supply of fresh bacteria in a "lagoon" - a chamber where bacteria and phages grow. This ensures that newly generated phages always have hosts to infect. Simultaneously, we flush out old bacteria and phages, ensuring that only those phages that replicate quickly enough can survive. In this setup, better-performing variants will thrive and outcompete others, driving evolution forward. To speed up this process, a special mutation plasmid (MP) is introduced into the bacteria. This plasmid increases the already high mutation rate of the phages, significantly accelerating the pace of evolution and allowing researchers to quickly refine biomolecules. Over time, phages with beneficial mutations accumulate and become dominant in the population. These mutations can then be identified by sequencing the phages. Finally, one often uses orthogonal methods to confirm the activity of the evolved biomolecule.
 
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+![Figure_pace](https://idec-teams.github.io/2024_Evolution_Suisse/img/PACE_related_schematics/onlypace.png)
+<figcaption> Figure X: A schematic representation of the Phage-Assisted Continuous Evolution (PACE) system. Once a phage infects the cell (1) it's genome (SP) enters it and the biomolecule that is being evolved is expressed (2). Through a genetic circuit on AP that links the biomolecule activity to _gIII_ expression, the protein pIII, required for phage propagation is expressed (3). In parallel, the phage genome is being replicated (4), with mutations occuring at a higher pace due to the presence of MP. Finally, the newly generated phage genome, strucutal proteins and pIII assemble into new phage particles. The resulting phages then go on to infect new cells. Should the variant be inactive, pIII is not produced, resulting in non-infectious phages from that cell. New cells are continuously pumped into the lagoon, while old cells and phages are pumped out.
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 Sometimes, the activity of the biomolecule we're evolving is too weak, resulting in slow phage propagation that makes it difficult to run PACE effectively. In such cases, we use a modified approach called Phage-Assisted Non-Continuous Evolution (PANCE). Unlike PACE, where phages and bacteria are continuously refreshed in a bioreactor (lagoon), PANCE works in a batch culture. In this method, phages are introduced into a batch of bacteria and allowed to propagate over a set period. Once the cycle is complete, a sample of the culture is taken and used to inoculate a new batch of bacteria, repeating the process. This non-continuous setup eliminates the risk of phages being removed from the culture faster than they can propagate, enabling evolution even when the activity of the biomolecule is low. PANCE is often used as a preliminary step before PACE, allowing us to first evolve the biomolecule to a higher activity level, which is then sufficient for running continuous evolution in the PACE system.
 
 ## References