Part:BBa_K4174001

osmY-mRFP1

This composite part is composed of UNS1 (BBa_K2680553), the osmY promoter (BBa_J45992) followed by a scar sequence (tactagag), the B0030 RBS (BBa_B0030) followed by a scar sequence (tactag), mRFP1 (BBa_K4174003) followed by a scar sequence (tactagag), the B0015 terminator (BBa_B0015), and UNS 10 (BBa_K2680554).

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  COMPATIBLE WITH RFC[12]
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  INCOMPATIBLE WITH RFC[25]

  Illegal AgeI site found at 823
  Illegal AgeI site found at 935
  
• 1000
  COMPATIBLE WITH RFC[1000]

Biological Relevance

The ability to assay whether a chassis is actively transcribing its circuit to make proteins is crucial for testing the efficacy of a fieldable construct. Bacteria have two main life stages - exponential growth, during which they reproduce and express their circuits with ease, and stationary phase, during which they cease most non-essential metabolic activity. Since stationary phase is induced by inopportune environments, such as metabolic shortage, most bacteria in nature exist in stationary phase (Jaishankar 2000). This is a major roadblock for fieldable synthetic biology, as constructs that work perfectly in the lab may stop expressing their circuit when introduced into their deployment sites. In order to assay how a circuit will behave in nature, constructs should be tested in the lab while in stationary phase.

Design Notes

This part uses an osmY promoter since this promoter is induced by the cell's entry into stationary phase. In typical E. coli cells, osmY, which helps cells transition into stationary phase when under osmotic or metabolic stress, is not produced during exponential growth phase but is produced during stationary phase. Specifically, the osmY promoter is induced by the rpoS (ribosome polymerase sigma S) at the onset of stationary phase (Chang 2002). Because this promoter is partnered with a sfGFP coding region, this construct fluoresces red once the cell has entered stationary phase.

• This composite part is an improvement of the 2006 MIT iGEM team's composite part BBa_J45995, which is a stationary phase detector utilizing osmY. We have replaced GFP with mRFP1 from Mutalik et al. 2013 and added unique nucleotide sequences (UNS) 1 and 10 sequences (Torella et al., 2014) to the ends.
• We elected to use monomeric red fluorescent protein (mRFP1) as opposed to the original GFP in order to provide an alternative reporter to GFP for the detection of stationary phase in bacterial cells. mRFP1 is a monomer, has a rapid maturity rate, and has minimal spectral overlap with GFP compared to the wild-type red fluorescent protein DsRed (Campbell et al. 2002). Creating alternative versions of fluorescent bioreporters using proteins with different excitation and emission wavelengths allows researchers to assay multiple parameters at a time, as different fluorescent assays conducted simultaneously must use proteins with different absorption spectra in order for researchers to differentiate between them.
• The sequence of our mRPF1 construct is compatible with the Type IIS assembly method, unlike the original construct. Constructs uploaded to the iGEM Parts Registry must be compatible with either Type IIS assembly or BioBrick RFC[10] assembly. The original MIT iGEM 2006 construct was only compatible with the BioBrick RFC[10] assembly method, but after altering the sequence as described above, our composite part is now compatible with both Type IIS assembly and BioBrick RFC[10] assembly.
• We added UNS1 and UNS10 (Torella et al., 2014) to make this part compatible with Gibson Assembly using the pSB1C3 backbone, as we also added UNS1 and UNS10 to this backbone.
• We also designed a similar green fluorescence system using sfGFP. For more information about this, visit parts page BBa_K4174002.

Testing and Results

To test the effectiveness of our mRFP1 construct (BBa_K4174001), our team transformed the original MIT iGEM 2006 construct (BBa_J45995), our mRFP1 construct, and our sfGFP construct (BBa_K4174001) into E. coli NEB5α cells and grew the various transformants in a plate reader. They were grown at 37°C. For red fluorescence measurements, we used an excitation value of 584 nm and an emission value of 610 nm. For green fluorescence measurements, we used an excitation value of 485 nm and an emission value of 528 nm. The values for red fluorescence are reported below. For information about green fluorescence measurements, see parts page BBa_K4174002.

Based on the graph above, the bacterial cells engineered with our mRFP1 construct appear to have entered stationary phase around 16 hours. As seen in the graph, our mRFP1 construct produces more red fluorescence than the original circuit. The other measurements taken are for our sfGFP construct and untransformed E. coli NEB5-α cells, both of which serve as negative controls for red fluorescence.

As seen in the image above, qualitative results reveal that our mRFP1 construct produces more red fluorescence than the original construct. Here, our mRFP1 construct is on the far left, and is visibly red.

Source

Mutalik, V. K., Guimaraes, J. C., Cambray, G., Lam, C., Christoffersen, M. J., Mai, Q. A., Tran, A. B., Paull, M., Keasling, J. D., Arkin, A. P., & Endy, D. (2013). Precise and reliable gene expression via standard transcription and translation initiation elements. Nature methods, 10(4), 354–360. doi.org/10.1038/nmeth.2404

References

Campbell, R. E., Tour, O., Palmer, A. E., Steinbach, P. A., Baird, G. S., Zacharias, D. A., & Tsien, R. Y. (2002). A monomeric red fluorescent protein. Proceedings of the National Academy of Sciences of the United States of America, 99(12), 7877–7882. doi.org/10.1073/pnas.082243699

Chang, D. E., Smalley, D. J., & Conway, T. (2002). Gene expression profiling of Escherichia coli growth transitions: an expanded stringent response model. Molecular microbiology, 45(2), 289-306.

Jaishankar, J., & Srivastava, P. (2017). Molecular basis of stationary phase survival and applications. Frontiers in microbiology, 8, 2000.

Torella, J. P., Boehm, C. R., Lienert, F., Chen, J. H., Way, J. C., & Silver, P. A. (2014). Rapid construction of insulated genetic circuits via synthetic sequence-guided isothermal assembly. Nucleic acids research, 42(1), 681–689. doi.org/10.1093/nar/gkt860