Throughout the year, we've been working hard on developing, testing, and re-designing our system. Here, we demonstrate that our system works!
Methionine is a viable method of growth control in co-cultures
First of all, we have demonstrated that our method of controling growht (MetE) is viable. While other research groups had previously shown that E. coli growth can be controlled by regulating methionine synthesis via the MetE gene , we've proven that this sytem also works for our new application (co-cultures). In a co-culture, it is important to consider not only how to control one population of bacteria, but also to think about how the other bacterial population might affect it/the sytem as a whole. This was one of the first things we set out to do by answering the question "Is methionine shared between cells". See our design page for more detail about the rational behind this experiment. See our results page for detailed results showing that methionine produced by one population of E. coli cells is neither secreted into the environment nor shared with other E. coli populations that aren't able to produce their own.
We can monitor two populations in a co-culture
Secondly, we have demonstrated that we can monitor changes of individual population numbers within a co-culture. In order to monitor and maintain our co-culture we needed a method to track what was happening with each of the populations over time. We did this by marking one of the two populations with a fluorescent protein (GFP). Then we used a flow cytometer to compare the number of fluorescent cells to non fluorescent cells in our culture. We confirmed that this method works by comparing our results from the flow cytometer to colony forming unit counts. See the experiment entitled "Measurement - GFP vs Non Fluorescent" in our lab book and design page for additional information.
We can control growth rates with lights
Lastly, we have demonstrated that we can control the growth rate of JT2 containing CcaS/R with lights. By varying its exposure to green light we can modify the doubling time of our culture. It can be seen on our results page that we can push JT2 to a slower doubling time when we expose it to full red light. We also showed that exposing JT2 to green light will increase its growth rate (in comparison to its growth rate under full red).
 A. Milias-Argeitis, M. Rullan, S. K. Aoki, P. Buchmann, and M. Khammash, “Automated optogenetic feedback control for precise and robust regulation of gene expression and cell growth,” Nature Communications, vol. 7, p. 12546, 2016.