Revision as of 09:23, 19 October 2019

EutSMN bacterial microcompartment

This is an improved version of part BBa_K2213012 from team Manchester 2017. We down-regulated the base expression by exchanging the RBS to a the very weak RBS J61100. EDIT

Usage and Biology

Characterization

To test if our part could now produce the EutM and EutN proteins at levels low enough so that it would not be toxic to the cells anymore, we redid the OD measurement with the original EutSMN part.

Approach

First we streaked colonies of DH5alpha transformed with this part on Tetc and ATC plates to get an initial idea of how much we need to use for our liquid culture (initial screen)

After these results we went on to measure OD of inoculated liquid cultures over 20 hours.

Procedures

100mL LB cultures were inculcated with a single colony from an overnight transformation of pSEVA441 vector ( low copy number plasmid) carrying this part. E. coli strain DH5alpha was used.

Cultures were grown for 4 hours at 37° 300 rpm and then induced with 4.5 ng/mL Anhydrotetracylcine (ATC) or 45 ng/mL Tetracycline (Tetc) and 1mM Arabinose ((+)araB) each. One culture was not induced (control).
All concentrations are to be interpreted as final concentrations in the liquid culture. 45 ng/mL Tetc/ATC = 0.1 uM

Measurements were taken each hour for 9 hours and a final measurement was taken after 20 hours.
ATC was used at 10x less concentration since its a much stronger inducer than Tetc and has lower toxicity.

Results

Initial screen

We streaked DH5alpha transformed with our improved part on plates carrying high and low concentrations of Tetc and ATC to get an idea as to how much to use to induce our liquid cultures.

Spectinomycin was added due to the resistance gene in our backbone.

Surprisingly a concentration of 45 ng/mL Tetc (0.1 uM) seemed low enough that the cells actually survived. At 1 uM Tetc or ATC the bacteria didn't grow well at all. This supports the hypothesis that EutN and EutM are toxic for bacteria at high levels.

An ON liquid culture of a 0.1 uM Tetc colony was pelleted and showed fluorescence under UV light, a good indicator that the proteins were actually produced.

OD measurement

We did an OD measurement, using the information from the plate streak essay to use appropriate amounts of inducers.

It seems that our very weak RBS J61001 is doing a good job at keeping the base expression levels low enough so that not a lot of the protein is produced. OD increase is fairly similar to the control, even after induction and the OD decrease after 20 hours is not as strong as in the original part.

Imaging

We confirmed that the proteins were being produced by imaging with a confocal microscope, samples for imaging were taken 5 hours after induction.

induced:

uninduced:

Conclusion

Our improved part, when transformed in a low copy number plasmid, can be used to produce the proteins EutM and EutN at low enough concentrations to not cause strong stress on the bacteria but at high enough concentrations for form BMC's.

This information could be used to apply this approach to other Eut-protein parts such as https://parts.igem.org/Part:BBa_K2213002

For information about the vector and parts we used, please visit the "design" page.

Results

It seems that our very weak RBS J61001 is doing a good job at keeping the base expression levels low enough so that not a lot of the protein is produced.

Imaging

We confirmed with imaging that the protein is produced at high enough levels to form compartment:

This picture was taken 10 hours past induction, the signal does not seem very strong but there were a moderate number showing micrompartments.

The control was also imaged:

Sequence and Features