User:James Chappell/Growth phase
| Figure 1.1 it can be seen that the growth rate of the E.coli containing the J45996 is higher than that of E.coli J45995. The reason for this seems unclear and if anything unexpected. The J45996 involves greatest burden of synthesis in the exponential phase and also has the added burden of expression associated with the inverter. One cause for this difference seen could be due to different cell densities in the overnight cultures added to fresh media at time 0.
Figure 1.2 and 1.3 shows the normalised [GFP] vs time. Normalised [GFP] was calculated by normalising by the OD600 and converting fluorescence into GFP using a calibration curve. As can be seen both cultures start with the a initial level of [GFP], this is due to synthesis in the overnight culture which is still present at time 0. From the GFP changes little for the first hour until cells begin to divide and a degradation term is introduced into our system (see simple model below). The degradation until synthesis begins for both constructs when cells enter early and late exponential phase. Overnight we see that the exponential phase promoter (J45996) maintains the steady-state seen at 6 hours overnight. The stationary phase promoter (J45995)increases in [GFP] overnight as the cell population enters the stationary phase and is most likely in a steady-state.
There is a lot of variation within the data collected for both figure 1.1 and 1.2. The reason is firstly because of the intrinsic variation of expression in E.coli. In addition this data was a combined effort of Imperial College London Synthetic Biology Course and was collected by a group of around 30 engineers and biologist. This combined data introduces experimental variation that will have contributed to the variation seen.