BBa_K2229300

The existing parts BBa_K342003 (ompR234 ORF) and BBa_K805015 (csgD ORF) were taken from the distribution kit. First BBa_K805015 was inserted behind a strong promoter + strong RBS (BBa_K880005) (figure 3-10) to make the intermediate BBa_S05397. At the same time, ompR234 was inserted before BBa_B0015 (figure 3-10) to make the intermediate BBa_S05398.

To make the final composite, a strong RBS (BBa_B0034) was inserted in front of BBa_S05398 to make BBa_S05399. FInally, BBa_S05397 was inserted before BBa_S05399 to complete the full construct BBa_K2229300 (figure 3-13). Sequencing results from Tri-I Biotech confirmed that our final construct is correct.

Hypothesis

We hypothesized that biofilm production would be upregulated (in increasing order) if we overexpress CsgD, OmpR234, or both (figure 3-14). Overexpression of CsgD would result in more curli monomers, but no transport proteins to carry the monomers out of the cell. Overexpression of OmpR234 would allow curli monomers to be exported and form fibers and biofilm. Finally, when both CsgD and OmpR234 are overexpressed, twice the amount of curli monomers should be made and exported to form fibers and biofilm.

SDS-PAGE Gel

The original parts, BBa_K342003 (ompR234 ORF) and BBa_K805015 (csgD ORF), were cloned into expression devices, Bba_K2229200 and Bba_K2229100, respectively. We observed the expected bands at 25 kDa for CsgD and 27 kDa for OmpR234. Cultures carrying BBa_K2229300 (CsgD and OmpR234 expression), however, showed two extra bands at 15 kDa and 30 kDa, which were not observed in cultures expressing either CsgD or OmpR234 alone. We looked into the other curli operon genes, and found that CsgG is around 30 kDa, whereas CsgA, B, C, E, and F are all around 15 kDa (Robinson et al. 2006; Uhlich et al. 2009; Shu et al. 2012). This suggests that, as expected, BBa_K2229300 stimulates the production of all curli proteins (predicted proteins and sizes are labeled in figure 3-15).

Congo Red Assay

After confirming protein expression, we wanted to test if our constructs actually lead to faster and more robust biofilm production. We used Congo Red (CR), a dye commonly used to measure biofilm production (Reinke & Gestwicki 2011). CR solution mixed with bacterial liquid cultures were transferred to 12-well plates with glass coverslips and incubated at 37˚C for one day. The samples were then washed with PBS and dried. Any stained biofilm on the glass coverslips was solubilized in ethanol, and absorbance was measured at 500 nm (figures 3-19). If biofilms were present, the solution would appear red, which could be quantified by an absorbance value.

Overexpressing CsgD or OmpR234 increased biofilm production, compared to controls with only csgD or ompR234 ORFs, as we hypothesized (figures 3-16 and 3-17). When all three expression constructs were compared, we find that overexpression of OmpR234 and CsgD together (BBa_K2229300) increased biofilm production the most (figure 3-19). BBa_K2229300 also increased adhesion to glass coverslips, and we could see a layer of biofilm which remained attached to the glass surface after the washing steps (figure 3-19, A).