Difference between revisions of "Part:BBa K342003"

Revision as of 20:24, 21 September 2011

OmpR234 protein, with higher effect on Curli promoter

This part is coding for a mutated version of the response regulator OmpR (J Bacteriol. 1998 180(9):2442-9). This protein will be phosphorylated by the associated-sensor EnvZ. This mutated phosphorylated protein is a better activator of the curli csgD promoter than the wild type OmpR. OmpR234 can activate the cryptic curli operons found in all known K12 strains, and then leads to the formation of thick biofilm on glass and polystyrene.

Usage and Biology

This part can be used to induce a constitutive biofilm producing phenotype in bacteria. OmpR234 is now used by several labs in the world (in USA for example, Cornell: Microbiology. 2011 157:1640-50 or Columbia: Water Res. 2008 42:3066-74) and the original paper describing this mutant has been cited 204 times.

Characterization (New data, 2011)

Microscopy tests

The pIG16 (BBa_J23119-OmpR234 in pSB1A2) and pIG3 (BBa_J23119 part in pSB1A2) were inserted in a strain constitutively expressing GFP, PHL1414 (MG1655 with a chromosomical insertion of GFP). The strains were respectively named S31 and S30.

In sterile empty plates, we introduced 10mL of M63G, with 100μL of Amp and 100μL of bacteria from an overnight liquid culture.

Then, we added 3 or 4 sterile glass coverslips and let them incubate at 30°C for 23 hours. If the strain produce some curli, it will form biofilm on the glass slides. We washed carefully the slides to eliminate non-adherent bacteria.

To determine if a biofilm was able to develop, we observed the surface of the contaminated coverslips with a fluorescent microscope. After a thorough visual scanning, several optic fields (at least 3)were photographed. One representative picture is presented here.

We can see that the strain containing the pIG16 plasmid is more adherent than the strain containing the control plasmid pIG3, and is able to produce thick biofilms on glass.

Conclusion: The BBa_J23119-OmpR234 part increases the stickiness of a part.

Quantitative adherence tests in plates

To obtain a quantitative characterization, the plasmids were introduced into the PHL1414 strain. The strain harboring the pIG16 plasmid is noted S31. The control strain with the pIG3 plasmid is noted S30.

The effect of each plasmid on the adherence was then measured in 24-wells plates. The strains were seeded as described here

Conclusion: The OD600 is not significantly different for the two strains, which shows there is no effect of the plasmid on the growth.

The percentage of adherence is now measured for both strains

The measure of the OD 600 of both the biofilm fraction and the planktonic fraction allow to calculate the percentage of adherence of the bacteria when the violet crystal staining of the attached bacteria will give us a first idea on the biofilm thickness.

Conclusion: There is a significant increase (p=0.0008 in student t test) of stickiness when the part BBa_J23119-OmpR234 is introduced.

Sequence and Features