Difference between revisions of "Part:BBa K216005:Experience"

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Applications of BBa_K216005

Edinburgh iGEM team, October 2009: To test this part, it was combined with lacZ minigene J33202 for Miller assays (giving part BBa_K216009), and also with GFP for analysis using the promoter characterization kit of Jason Kelly. Results from overnight induction with Miller assay indicated stronger induction by nitrate than nitrite. A time course of induction using the GFP construct also indicated that nitrate gave stronger induction in the first few hours.

Results from Miller's Assay




Results from GFP promoter characterization kit
PyeaR response to nitrates
Jason Kelly’s assay demonstrates that our promoter is sensitive to nitrates. The most sensitive time period is between 5 ½ hours (320 minutes) 7 ½ hours (440 minutes) after induction. The sensitivity decreases with time, but induction is still at a high level after the peak activity of the promoter. Only two concentrations are shown (0 mM and 10 mM), as we have demonstrated that 10 mM is the sensitivity peak of this promoter (look at last graph).

PyeaR response to nitrites
Jason Kelly’s assay demonstrates that our promoter is sensitive to nitrites. The fluorescence levels begin to build up only after about 8 hours; therefore other irrelevant results are omitted from this graph. The sensitivity curve in this case is less steep compared to the one produced due to the presence of nitrates. This indicates that the promoter responds differently to these two nitrogenous compounds. Again, only two concentrations are shown (0 mM and 10 mM), as sensitivity peaks at 10mM.

PyeaR response to nitrates and nitrites after overnight induction
Here we can compare the activity of this promoter to different concentrations of both nitrates and nitrates. We observed that the promoter is activated more readily by nitrates compared to nitrites. Nevertheless, the activation produced by nitrites remains significant. The peak activation concentration for both compounds is 10 mM, after which activation efficiency decreases.

User Reviews

UNIQ2fa2eea0a51e33c6-partinfo-00000000-QINU UNIQ2fa2eea0a51e33c6-partinfo-00000001-QINU

NRP-UEA 2012

The team decided to develop the PYEAR biobrick further by ligating it to its mammalian counterpart: CArG promoter sequence E9-ns2. The genes were synthesised in two orientations, bacterial-mammalian (BBa_K774000) and mammalian-bacterial (BBa_K774001) as initially we were not sure what effect gene order would have on gene activity. The aim of this development was to increase the flexibility of the PYEAR promoter so that it can be used in both mammalian and bacterial systems. This is something that we thought was important as sensing nitric oxide in the human body has a wide range of therapeutic applications (please see the future applications section on our wiki).

This characterisation included:

-Growth studies of the PYEAR biobrick, the mammalian-bacterial (M-B) biobrick, and the bacterial-mammalian (B-M) biobrick.

-Measuring the fluorescence of the M-B biobrick ligated with Red Flourescent Protein (RFP) and enhanced Cyan Fluorescent Protein (eCFP), as well as the B-M biobrick ligated with RFP and CFP, in response to induction with different potassium nitrate concentrations.

-Measuring the number of cells which fluoresce in different potassium nitrate concentrations using flow cytometry.

Growth Studies

A comparison between the growth of E.coli cells, before and after transformation with PyeaR + GFP (BBa_K381001) and B-M and M-B (in pSB1C3)

The study involved testing the affects of transforming E.coli with different promoters on its growth over time. The promoters E.coli had been transformed with were PyeaR, M-B and B-M. These are promoters which all react to nitrogenous species. By running these together, we can obtain a direct comparison between all three of these promoters on the growth of E.coli. To see if there are any significant changes, the study was run alongside E.coli cells which had not been transformed with anything. For the rest of this brief report, untransformed cells will be referred to as Alpha cells and the other E.coli cells with transformations will be referred to as the promoter with which they were transformed with.

The E.coli cells used in the study and for the transformation are the same type of cells (Alpha select gold standard cells from Bioline). A colony was inoculated into 5ml of LB media overnight and the cells spun down the following morning and diluted with fresh LB until an OD reading at 600nm of 0.2 ± 0.01 was obtained. Three repeats were made of each sample.

The study lasted for 12 hours. An OD reading at 600nm was taken once an hour. Between the hour, the cuvettes were put into a 37ᵒC incubator to encourage growth and for standardising measurements with other growth studies. To calculate the number of cells in the samples, a calibration curve was set up. This involved using cultures of the E.coli cells without transformations. The E.coli cells were diluted with different volumes of LB and OD readings were taken as well as plating on Agar plates. After a day of growth, the numbers on these plates were counted and recorded. The CFU/ml was calculated. When the OD readings (x axis) and the CFU/ml (y axis) readings are plotted, the equation of the line of best fit, gives a conversion for the absorbance readings. This allowed us to measure the growth. This is demonstrated in figure 1.

Figure 1. Calibration curve to calculate the conversion factor between OD reading at 600nm and the number of colony forming units growing per ml (CFU/ml)

We found that there was a significant difference between Alpha cells and PyeaR cells. Initially, Alpha cells had a greater growth rate, but after the third hour into the study, the growth rate of PyeaR was faster than that of Alpha cells. The overall growth rate of PyeaR cells was significantly faster that Alpha cells (Levenes Test, F = 1.009 p = 0.372; T Test, t = 4.196, df = 4, p = 0.014).

Figure 2. Growth of PyeaR transformed E.coli cells relative to Alpha cells (untransformed cells). Error bars show the standard deviation between the three repeats. For clarity reasons, lines of best fit are not shown The growth pattern and rate of E.coli cells with or without transformation with B-M and M-B show little difference. Any differences in growth rate were not significant. There was lots of overlap. As previously described, there was a significant difference between the growth rate of PyeaR and Alpha cells. There was also a significant difference between MB/BM and PyeaR cells. The statistical results can be seen in Table 1.

Figure 3. Growth over 12 hours of Alpha, M-B and B-M. Error bars and lines of best fit are not shown for clarity reasons.

Table 1: ANOVA readings of statistical differences between Alpha (1) PyeaR (2), MB (3) and BM (4).

From all the above graphs, it can be seen that with the starting concentration of cells as high as they are, the cultures are in exponential stage and do not undergo lag phase. A further growth study will be carried out on purely the lag phase with lower starting concentrations. As the starting absorbances here are approximately 0.2 at a wavelength of 600nm, the lag phase study will involve starting absorbances of 0.04 and lower.

A comparison between the growth of E.coli cells, before and after transformation with PyeaR + GFP (BBa_K381001) and B-M and M-B (in pSB1C3)- Lag Phase Study

Following the above study, we found that a lag phase only study needed to be carried out to see if there was a significant difference in the lag phase. Again the study protocol was the same except that the starting concentration absorbances at 600nm was lowered to <0.04. It was extremely difficult to keep the absorbances ranges within 0.005 so the range is actually 0.3±0.1. The below graph shows the mean average of all the data; using the data from the calibration curve, the absorbances were converted to colony forming units per ml (CFU/ml). The trend lines of alpha cells, BM/MB and PyeaR transformed cells are shown within this order from highest to lowest trendlines. One single trendline was used to represent BM and MB because the actual trendlines were extremely similar. Using the initial concentrations of 0.3±0.1 showed that there is little difference between the growth rates. Using statistical analysis, it was found that there was no significant difference between any of the transformed cells relative to Alpha cells or to each other (Anova, p > 0.05).

From this study we have found that changes in growth occur during exponential growth phase and not the lag growth phase.

A study of growth of PyeaR in different concentrations of potassium nitrate

Characterisation of BM and MB in different concentrations of potassium nitrate

Following the experiment measuring the affect on the intensity of GFP fluorescence of PyeaR-GFP at different concentrations of potassium nitrate, a study on how different levels of potassium nitrate affect fluorescence intensity of BM and MB attached to fluorescent proteins was tested. Where previously the study was carried out in a qualitative fashion, this was carried out to collect data quantitatively using a fluorometer. Overnight cultures of BM and MB attached to RFPs and CFPs containing different levels of potassium nitrate prepared. Using 5ml of the cultures, cells were peletted. The overnight cultures contained different concentrations of potassium nitrate (0mM, 5mM, 10mM, 15mM and 20mM). These cells were then resuspended and lysed (full protocol on protocol page). These cultures were then diluted using Tris buffer (0.5ml sample to 1.5ml buffer). Readings from the fluorometer wavescans were recorded.

Comparing BM and MB with CFP fluorescence showed that BM-CFP intensity is relatively low when compared to MB. MB seems more sensitive to nitrate levels than BM. However, for both, it seems that once a threshold of nitrate levels is reached, there is not additional expression. Beyond this concentration, the intensity drops. This may be due to a number of factors. The cells may die due to overload of proteins which may have a toxic affect. For BM this threshold seems to be just above 20mM and for MB this appears to be around 15mM. This is seen in the figure below.

Comparing BM and MB with RFP fluorescence showed a similar result to the CFP study. However, both BM and MB have similar sensitivities to potassium nitrate levels, BM seems to be more sensitive to potassium nitrate concentration this time. From this study it is clear that beyond a certain concentration of nitrates, the fluorescence intensity stops increasing and decreases instead. Again, this may be due to the capacity or tolerance of the cell to hold the volume of fluorescence. protein.

Transfection of BM and MB into mammalian cells

The two hybrid promoters were ligated with RFP (BBa_K774007 and BBa_K774005)and CFP (BBa_K774004 and BBa_K774006) in order to characterise them further.

Pellets of E. coli transformed by this part ligated to BBa_E0420 (an RBS and CFP reporter) and grown in media with added concentrations of potassium nitrate. Going from left to right in concentrations of potassium nitrate: 10 mM, 50 mM, 100 mM and 0 mM

This image (right) shows competent cells transformed with part: BBa K774004 and grown in media containing potassium nitrate (as a source of nitrates in order to induce promoter activity) at concentrations of 0 mM, 10 mM, 50 mM and 100 mM (from right to left). The E. coli was grown for 6 hours and then added to eppendorf tubes and spun down in a centrifuge in order to produce a pellet. The four samples were then viewed under a UV box to assess for fluorescence; as the photograph to the right shows that the sample at 0 mM potassium nitrate did not fluoresce, however those at 10, 50 and 100 mM potassium nitrate did fluoresce. They also appeared to fluoresce at the same strength, suggesting that 10 mM was equal to or above the maximum sensitivity level of this part.

The graph above shows the flourescence measured from the expression of eCFP due to the response of the bacterial-mammalian promoter to different concentrations of potassium nitrate. The wavelength reading which corresponds to eCFP is between 440-500nm. The graph clearly demonstrates that between 0mN and 15mM there is a proportional relationship between fluorescence intensity and potassium nitrate concentration. There appears to be a sharp increase in fluorescence intensity between 5mM and 10mM, and the rate at which intensity increase gradually decreases so that there is only a small increase between 15mM and 20mM.

The graph above shows the flourescence measured from the expression of eCFP due to the response of the mammalian-bacterial promoter to different concentrations of potassium nitrate. The wavelength reading which corresponds to eCFP is between 440-500nm. The graph clearly demonstrates that between 0mN and 15mM there is a proportional relationship between fluorescence intensity and potassium nitrate concentration. It can be noted that at a 20mM concentration the intensity of fluorescence sharply decreases back down to the level of 5mM potassium nitate concentration. This may be due to the cell overexpressing eCFP up to the point at which the excess protein begins to form inclusion bodies which can no longer fluoresce; alternatively, this could be due the potassium nitrate concentration reaching the critical concentration at which it becomes toxic to the cell. This data differs to the readings taken from the bacterial-mammalian promoter ligated to eCFP, as well as the hybrid promoters to RFP, which may suggest there is a difference in the molecular mechanisms that these promoters function by; however at this point the change in intensity at 20mM is inconclusive and is an area which we would like to look into further.

We were initially unsure of the effect that the orientation of the bacterial (pYEAR) and the mammalian (CaRG) genes would have in gene expression, therefore we synthesised two hybrid promoters in the orientation bacterial-mammalian and mammalian-bacterial. The graph above compares the intensity of fluorescence of the two hybrid promoters (BBa_K774004 and BBa_K774006) ligated to eCFP. There is a distinct difference between the intensity of fluorescence produced by the bacterial-mammalian promoter and the mammalian-promoter which is something that we would like to look into further. It is particularly interesting that at an intensity of 109a.u. the mammalian-bacterial promoter returns to the same level of intensity as the apparent maxiumum of the bacterial-mammalian promoter at 40a.u.