Part:BBa_K802001
Dispersin generator for B. subtilis
This part associates the Bacillus subtilis constitutive promoter (Pveg) with dispersin B gene (dspB).The dspB gene codes for an enzyme which catalyzes the hydrolysis of the extracellular matrix produced by Gram negative bacteria.
Characterization
Following results show that the BBa K802001 part allows B. subtilis 168 strains to scatter S. aureus and Staphyloccocus epidermids cells in a biofilm.
In our plasmid collection, this part is refered to pBK33 when cloned into the pSB1C3 (CmR) backbone, and pBKH41 when cloned into the high copy shuttle vector E. coli – B. subtilis. The corresponding negative control is the empty shuttle vector (pBKH26 in our collection). The plasmid pBKH41 was introduced into both E. coli NM522 and Bacillus subtilis 168 strains to assay its scattering performance.
If you have any question on the following experiments, don’t forget that all the informations relative to our strains, plasmids and protocols are on our wiki notebook.
Confocal Microscopy 
Bacillus subtilis 168 was transformed with pBKH41 (dspB in the shuttle vector) and with pBKH26 (empty shuttle vector as a negative control). These two strains were grown on LB medium supplemented with erythromycin (15µg/mL) for 24h at 30°C without shaking to provide the swimmers "biofilm killer".
We verify the inocuity of our constructs on B. subtilis. With or without vector we found that B. subtilis was able to swarm the plate overnight. Our tests also show that B. subtilis is a much better swimmer than E. coli.
Motility plate assays
Biofilms of the S. aureus fluorescent strain RN4220 pALC2084(GFP-tagged) were cultivated in 96-wells microtiter plates. This strain is a nonmotile laboratory strain.
Biofilms with or without addition of B. subtilis were then observed under a time-lapse confocal microscope as described (see protocol). GFP was excited at 488 nm with an argon laser, and fluorescent emission was collected on a detector in the range of 500-600 nm. Biofilms were observed by 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 : untreated S. aureus biofilm.
Negative control : S. aureus biofilm treated with B. subtilis containing the shuttle vector without the dspB gene.
S. aureus biofilm treated for 4 hours with B. subtilis containing the part BBa_K802001 carried by the shuttle vector.
Our results demonstrate that the part BBa K802001 leads to the almost complete S. aureus biofilm dispersal
Quantitative image analysis :
A quantitative analysis was performed 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.
- Substratum coverage (%) : it corresponds to the area coverage in the first image of the stack (i.e. at the substratum). It is a good mean to estimate how efficiently the substratum is colonized by bacteria of the population.
Quantification of Staphylococcus epidermidis biofilm thickness after Dispersin treatment
In order to measure and to appreciate the Dispersin effect on Staphylococcus epidermidis biofilms, tests were conducted in two different systems : in microtiter plates and on glass lamella in test tubes.
Microtiter plates : Each well was inoculated with a 1:100 dilution of a 24h TSB Staphyloccocus epidermids preculture. From crystal violet staining, we can easily see that untreated S. epidermidis biofilms adhere to the well walls. The adherence is estimated from OD600 to be ca. 75%. However the Staphylococcus epidermidis biofilm on polystyren or glass coverslip was found too fragile for the manipulation required to test the dispersin effect.
The same kind of tests were done in test tubes containing coverslip. The results are similar to those done on microtiter plates biofilms is destroyed even in presence of the negative control.
OD600 Test
We measured OD600 to demonstrate the effect of dispersin on S. epidermidis. This test shows that dispersin has a limited effect on a bacterial suspension of S. epidermidis. This result was expected since dispersin only scatters bacterial aggregates and thus does not reduce the number of cells which is measured when we take OD600.
SDS-PAGE Protein gel
No massive production of dispersin could be observed in E. coli nor in B. subtilis supernatant, even after a 4X concentration by acetone precipitation (data not shown).
Combined action between the parts BBa_K802000 and BBa_K802001
As we demontrated with the previous tests, the part BBa_K802001 has a real effect on the S. aureus biofilm. For our Biofilm Killer project, two complementary agents (lysostaphin with the part BBa_K802000 and dispersin with the part BBa_K802001) were used to destroy an installed biofilm. Thus, it was interesting for us to combine these two agents.
We have also made new tests on 96-well plate, according to the same protocole than the one used to characterize the lysostaphin part with the confocal microscope. The only difference was that we added 125µL of B. subtilis with the part BBa_K802000 and 125µL of B. subtilis with the part BBa_K802001.
Two cases are analysed :
- Negative control : it is a S. aureus biofilm treated with B. subtilis strains containing the shuttle vectors without the Lysostaphin and Dispersin genes.
- Strain with our parts : it is a S. aureus biofilm treated with B. subtilis strains containing the part BBa_K802000 and BBa_K802001 in their shuttle vectors.
S.aureus biofilm treated with the shuttle vectors without the lysostaphin and the dispersin genes (Negative control)
S.aureus biofilm treated with the strain containing parts BBa_K802000 and BBa_K802001
Our results clearly show the dramatic increase in efficiency of Biofilm Killer, which expresses the lysostaphin and dispersin parts in combination, over the other Bacillus subtilis strains harboring only the lysostaphin or dispersin parts.
Usage and Biology
This part was designed to be used in Bacillus strains in order to scatter biofilms including Staphyloccocus aureus biofilm which we have used here.
Possible applications include biofilm treatment in medical domain, oil or food-processing industries, using this scattering property to eliminate harmful biofilms.
Sequence and Features
- 10COMPATIBLE WITH RFC[10]
- 12COMPATIBLE WITH RFC[12]
- 21COMPATIBLE WITH RFC[21]
- 23COMPATIBLE WITH RFC[23]
- 25INCOMPATIBLE WITH RFC[25]Illegal NgoMIV site found at 675
- 1000COMPATIBLE WITH RFC[1000]
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