Part:BBa_K1583112
pRha + CsgA & GFP in same operon
CsgA is a protein monomer which can aggregate to form amyloid nanowires in natural biofilms of E.coli. The aggregation to the nanowire ('curli') is induced by the membrane protein CsgB. CsgC, CsgE, CsgF and CsgG act as chaperones for CsgA during translation and export CsgA to the extracellular space.
This part was designed to measure intracellular expression rates of CsgA coupled to fluorescence (GFP) by cloning the biobrick BBa_I13504 into the same operon which is under control of the Rhamnose promoter.
A biofilm is created, when sufficient levels of mature CsgA are present in the extracellular space. CsgB can then act as a nucleator inducing the curli formation.
On the way there, many questions need to be answered.
To do this in the most efficient way, we went back to good old modeling.
Transcriptional and translational rates can be approximated with reasonable precision. However, we wanted to measure this!
To do so, we created this device. The beginning of the device consists of our standard parts: the rhamnose promoter and the CsgA gene.
However, we skipped the terminator behind the gene.
In this manner we were able to clone the gene from the biobrick BBa_I13504 coding for GFP behind CsgA and into the same operon.
We assume that the difference between CsgA and CsgA+GFP in size does not influence transcription and translation of CsgA. Using a calibration curve connecting fluorescence [au] and mass [ng] we were able to calculate the expression rate of CsgA with units [proteins/(cell*second)].
This part was created to test the functionality of the rhamnose promoter and to measure intracellular steady state concentrations at different induction levels of rhamnose. Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21COMPATIBLE WITH RFC[21]
- 23COMPATIBLE WITH RFC[23]
- 25COMPATIBLE WITH RFC[25]
- 1000INCOMPATIBLE WITH RFC[1000]Illegal BsaI.rc site found at 1308
Characterization
This part was characterized in three different experiments:
Fluorescence assay
To be able to ensure that CsgA is expressed, we used this biobrick to check that the rhamnose inducible promoter works. In this experiment, the fluorescence signal of our CsgA construct and CsgA-GFP construct was recorded in time after induction with no, 0.2% (w/v) or 0.5% (w/v) rhamnose. Besides the fluorescence, the OD600 was measured in order to normalize the fluorescence signal per cell. All conditions were carried out in triplicates to be able to do a statistical analysis on the data. The different experiments were induced in a 96 well plate. The OD600 and fluorescence signal was recorded in a plate reader during a 18 hour period of induction at 30°C.
In Fig. 1, the fluorescent signal was normalized by the number of cells and plotted as a function of time. The red bars denote the error within each ID.
As can be seen from Fig. 1, only the experiments with 0.2% (w/v) and 0.5% (w/v) rhamnose induction with this biobrick gave a clear increase in fluorescence signal in time. All other experiments, gave similar levels of fluorescence, slightly increasing in time. Furthermore, it can be seen that a higher induction level of rhamnose leads to an increase in GFPmut3 and thus fluorescence. Finally, as the fluorescence signal is normalized by the cell density, one can make statements about the activity of the rhamnose promoter. The promoter seems to not be active right after induction, but more after 3 or 4 hours. This is in accordance with data from literature (Wegerer et. al), in which a low amount of fluorescence with a rhamnose promoter was observed after 2 hours of induction.
With this kinetic experiment, we have proven that the rhamnose promoter does indeed induce the expression of the csgA gene and the I13504 gene.
Transmission electron microscopy
Using TEM the formation of curli of the biobrick BBa_K1583100 was visualized. Although this is a different biobrick (no GFP gene behind the same promoter), curli formation can be presumed to be similar for this biobrick.
We did not observe formation of curli nanowires in the uninduced cultures of our strain. However, cells from induced cells clearly produced them, as supported by the TEM images.
| None |