Part:BBa_K911004:Experience

During and after assembly of this sequence, unexpected toxicity issues were observed. This necessitated its assembly in a low copy number vector. This part is submitted to the registry as is, in the suitable backbone provided by the synthesis company (with permission from HQ). We strongly recommend that you do not attempt to assemble it in psB1C3, as it will kill your cells. It might also be advisable (if not essential) to transform this into an e.coli strain that can tolerate toxic inserts reasonably well, such as XL1 blue.

The toxicity of the construct causes strong selective pressure against it, and characterisation has been hampered by the tendency of cells to lose parts of the insert, although it does seem to be fairly stable across subsequent replating if it is retained on the initial transformation plate. Orange fluorescence co-segregates with luminescence: colonies that lose their orange colour also lose luminescence (colonies are constitutively luminescent), as shown.

These patches are derived from either white or orange colonies on the original transformation plate

This image shows the constitutive luminescence of each patch

We suspect that the repeated terminator may facilitate recombination, and another team might wish to investigate whether replacing the second terminator aids stability.

The construct is not behaving entirely as expected, as the e.coli colonies are initially orange, despite mOrange being lacI-repressed. This is probably due to leakage, as the RBSes are very strong in both e.coli and bacillus, and retrospectively could have been predicted. This could be indicative of high sensitivity to promoter activity, which is by no means a bad thing!

We ran out of time before attempting to insert this into bacillus. Bacillus homology regions would need to be added, but on the upside, the much lower copy number would likely counteract the toxicity issues.

Applications of BBa_K911004

BBa_k911004 was designed to act as a quantitative reporter construct. It still has potential for this, but the toxicity/stability issues should be addressed.

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