Difference between revisions of "Part:BBa K802003"

Revision as of 19:02, 26 September 2012

Shuttle vector for E. coli and B. subtilis

This part is a shuttle vector of 6.5kb which is Ampicillin resistant in E. coli and Erythromycin resistant in B. subtilis. It is a low copy number plasmid in B. subtilis and a high copy number plasmid in E. coli.This plasmid is a derivative of pHT315 [2] in which the polylinker has been reconstructed to meet the IGEM standard. It has a polylinker containing all 4 of the iGEM restriction sites.

Sequence and Features

Characterization

Transformation yield

In E.coli NM522 strain, the average yield was 3.7 x 10⁶ cells/µg. The transformed cells were selected on LB medium supplemented with Ampicillin at a concentration of 100µg/mL.

In B.subtilis 168 strain, the maximum yield was 71 cells/µg. The transformed cells were selected on LB medium supplemented with Erythromycin at a concentration of 15µg/mL.

Antibiotic resistance

Given the fact that this shuttle vector is very similar to BBa_K802004, the two of them were tested in parallel. Two experiments were made in order to characterize the antibiotic resistance of the shuttle vectors : the first one on Agar plates and the second one in liquid cultures. In both cases the medium was LB supplemented with Ampicillin or Erythromycin at different concentrations.

The shuttle vector was transformed into the NM522 strain in order to be tested.

A) Agar plates
Saturated cultures containing the shuttle vectors were diluted 10, 100, 1,000 and 10,000 times. A volume of 5 µL of each solution containing the strain with BBa_K802003 part (the saturated culture and the 2 diluted solutions) was laid on the plate. The volume of the cultures containing the second shuttle vector (BBa_K802004) was adjusted regarding OD₆₀₀ in order to spot approximately the same number of bacterial cells.

As it can be seen in the picture, at 10 mg/mL (i.e. 100 times the usual selective concentration) there is bacterial growth, even for the culture diluted 10,000 times (the corresponding inoculum is indicated by the number 4 written on the plates on the picture)

B) Liquid cultures

Multiple tubes containing LB medium and Ampicillin at different concentrations ranging from 0 to 3 mg/mL are inoculated with bacteria containing the shuttle vectors BBa_K802003 and BBa_K802004. 3 samples per Ampicillin concentration were tested for each vector. As a negative control an Ampicillin sensitive strain was used to inoculate a solution of LB medium at the usual selective concentration of 100 µg/mL. The results are shown below :

To sum up, there is no significant difference concerning the Ampicillin concentration tolerance between the two strains, therefore between the two shuttle vectors as far as E. coli strains are concerned. At 2.4 mg/mL there is no bacterial growth for either strain.

The shuttle vector was transformed into Bacillus subtilis 168 strain in order to be tested.

A) Agar plates
Saturated cultures containing the shuttle vectors were diluted 100 and 10.000 times. A volume of 5 µL of each solution containing the strain with BBa_K802003 part (the saturated culture and the 2 diluted solutions) was laid on the plate. The volume of the cultures containing the second shuttle vector (BBa_K802004) was adjusted regarding OD₆₀₀ in order to lay approximately the same number of bacterial cells.

As it can be seen on the picture, at 300 µg/mL there is bacterial growth, even for the culture diluted 10,000 times (the corresponding inoculum is indicated by the number 4 written on the plates on the picture). However, for the strain containing BBa_K802003 part at 300 µg/mL Erythromycin, a difference for all 3 inocula compared to the first plate at 15 µg/mL can be pointed out, as opposed to the strain containing BBa_K802004 part (where there is a significant difference only for the culture diluted 10,000 times).

B) Liquid cultures

Multiple tubes containing LB medium and Erythromycin at different concentrations ranging from 0 to 1.5 mg/mL are inoculated with bacteria containing the shuttle vectors BBa_K802003 and BBa_K802004 (strains BK49 and BK50 in our collection). After 20 hours of incubation at 37°C, OD₆₀₀ of the cultures was measured. Afterwards, OD₆₀₀ value was converted in cfu/mL^[1].The results are shown below :

Sequencing of the modified regions

The two modified regions of the shuttle vector were verified by sequencing. The primers were designed using the sequences from the original plasmids that were used to construct the shuttle vector pHT304. Each primer was designed 100 bp upstream (and downstream) the modified sequences. The sequencing confirmed the expected sequence for the iGEM polylinker and the deletion of the SpeI site from the Bacillus coding sequence.

Usage and Biology

It can be used to transform E. coli and B. subtilis strains. However, it is highly recommended to amplify the plasmid before transforming a B. subtilis strain because the transformation yield is low compared to E. coli.

Functional Parameters

The tests showed that in E. coli NM522 strain there is bacterial growth in LB medium containing an Ampicillin concentration up to 1.2 mg/mL. Concerning B. subtilis 168 strain, the bacteria transformed with this plasmid could be selected with Erythromycin concentrations up to 0.9 mg/mL.

References

^[1] http://bionumbers.hms.harvard.edu//bionumber.aspx?id=105453&ver=1
^[2] Construction of cloning vectors for Bacillus thuringiensis. Arantes O. and Lereclus D. (1991) Gene 108:115-119.