Part:BBa_K1583112

pRha + CsgA & GFP in same operon

This part is meant to express the csgA and GFPmut3 gene under control of L-rhamnose-inducible promoter.

CsgA is a protein monomer which can aggregate to form amyloid nanowires in natural biofilms of E.coli. This protein is transported as an unfolded protein out of the cell. Outside the cell CsgA proteins self-assemble into nanowires after nucleation on the membrane protein CsgB. CsgC prevents CsgA proteins from self-assembling inside the cell and the transport is ensured by the proteins CsgEFG.

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.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal BsaI.rc site found at 1308
  

Characterization

This part was characterized in two different experiments:

• Fluorescence assay
• Transmission electron microscopy

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 figure 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.

Figure 1: Fluorescence signal normalized by the number of cells for 0% (w/v), 0.2% (w/v) and 0.5% (w/v) rhamnose with the csgA and csgA-GFPmut3 construct. The error bars are included for all experiments.

As can be seen from figure 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 (Figure 2). Although this is a different biobrick (no GFP gene behind the same promoter), curli formation can be presumed to be similar for this biobrick.

Figure 2: TEM images (magnification 7300 x). The left picture shows uninduced cells (0% Rhamnose).The picture on the right shows cells incubated with 1% (w/v) rhamnose.

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.

References

Wegerer, A., Sun, T., and Altenbuchner, J. (2008). Optimization of an E. coli L-rhamnose-inducible expression vector: test of various genetic module combinations”, BMC Biotechnology, 8:2