Part:BBa_K802000

Lysostaphin generator for B. subtilis

This part associates the Bacillus subtilis Constitutive Promoter (PVeg) with the lysostaphin gene. Lysostaphin is a bacterial biocide isolated from Staphylococcus simulans and which specifically cleaves the pentaglycine cross bridges found in the staphylococcal peptidoglycan. It contains the necessary RBS to work. With this part, Bacillus subtilis strains cause the lysis of Staphylococcus aureus cells.

Characterization

Following results show that this part allows B. subtilis 168 strains to kill the S. aureus and epidermidis cells.

In our plasmid collection, this part is named pBK23 in the backbone Chloramphenicol and pBKL28 in the shuttle vector E. coli – B. subtilis. The corresponding negative control is the shuttle vector (pBKL25 in our collection). We worked with the plasmid pBKL28 for the tests and we tried two different genetic backgrounds: the strain NM522 to make test in E. coli and the strain 168 to make test in Bacillus subtilis.

In you have any question on the following experiments, don’t forget that all the information relative to our strains, plasmids and protocols are on our wiki notebook.

Confocal Microscopy

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Biofilms are formed by the S. aureus fluorescent strain RN4220 pALC2084 expressing GFP. It is a nonmotile laboratory strain, used to form biofilm in 96-well microscopic-grade microtiter plate.

Bacillus subtilis 168 transformed by pBK28 (lysostaphin in the shuttle vector) and by pBKL25 (the shuttle vector without any gene to have a negative control) were grown on LB medium supplemented with erythromycin (15µg/mL).
After 24h of culture at 30°C without shaking, biofilms were observed under a time-lapse confocal microscope.
Cells expressing GFP were excited at 488 nm with an argon laser, and fluorescent emission was collected on a detector in the range of 500-600 nm using an oil-immersion objective with a magnification of 63x. The overall three-dimensional structures of the biofilms were scanned from the solid surface to the interface with the growth medium, using a step of 1 µm.
The 3D constructions were obtained with IMARIS software.

Three cases are analysed :

-Blank : it is a non treated S. aureus biofilm (just with growth medium).
-Negative control : it is a S. aureus biofilm treated by B. subtilis containing the shuttle vector without the Lysostaphin gene.
-Strain with our part : it is a S. aureus biofilm treated by B. subtilis containing the part BBa_K802000 in the shuttle vector.




S.aureus biofilm not treated (Blank)






S.aureus biofilm treated by the strain with the shuttle vector without the lysostaphin gene (Negative control)






S.aureus biofilm treated by the strain with the part



Conclusion:
With these observations, we concluded that the part causes the death of a large part of the S. aureus cells which constitute the biofilm. There is also a good expression of the lysostaphin in the B. subtilis strain, thanks to this part.




Statistic analysis:


In order to quantify our results, we made a statistical analysis with the MATLAB software. Different parameters [1] were used to quantify the biofilm, particularly :

- Total Biovolume (µm³) : it corresponds to the overall volume of the biofilm and also allows to have an estimation of the biomass in the biofilm.
- Mean thickness (µm) : it corresponds to the spatial size of the biofilm.

The same three cases as previously are analysed.









Conclusion:
These statistical results demonstrate that the S. aureus biofilm treated by the B. subtilis with the part is considerably reduced. Indeed, the total biovolume of the biofilm and its thickness strongly decrease after the treatment.
Moreover, the lysostaphin causing the lysis of the cells, we don't need to wash the biofilm to see the results, unlike the dispersin action (to refer to the results for the part BBa_K802001).

[1]Quantification of biofilm structures by the novel computer program COMSTAT. Heydorn A, Nielsen AT, Hentzer M, Sternberg C, Givskov M, Ersbøll BK, Molin S.Molecular Microbial Ecology Group, Department of Microbiology, Technical University of Denmark, DK-2800 Lyngby, Denmark.July 2000.




SDS-PAGE Protein gel


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The SDS-PAGE was run in order to determine the production of lysostaphin by Bacillus subtilis. Pellets and supernatants were analyzed.
The following image shows the protein after migrating the lysostaphin producer strain's pellet. The gel shows a low level of lysostaphin's production, probably due to pellet's storage conditions. Indeed, lysostaphin showed some unstability.







Supernatants were also used as samples, however they were not concentrated enough therefore the gel was not conclusive.





OD(600nm) Test


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Combined action between the parts BBa_K802000 and BBa_K802001


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S.aureus biofilm treated by the shuttle vectors without the lysostaphin and the dispersin genes (Negative control)






S.aureus biofilm treated by the strain with the Parts BBa_K802000 and BBa_K802001






Usage and Biology

This part was designed to be used in a motile strain like Bacillus subtilis 168 or Bacillus thuringiensis in order to cause the lysis of the Staphilococcus aureus cells. The motility of the strain makes its penetration inside the biofilm easier.

Sequence and Features




Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 1316
  
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  COMPATIBLE WITH RFC[1000]