Revision as of 00:48, 22 October 2009

Arabinose sensor: the pBAD promoter

Overview

In order to make an analog biosensor, we need our traffic light to produce distinct, unique responses to a range of concentrations of an input. However, the Registry is lacking in variable strength inducible promoters. We designed two variants of the pBAD promoter, one weaker and one stronger than wild type, based on AraC binding experiments performed by Niland et al.

Schematic black-box representation of the E. coli Biosensor that detects various concentration inputs and color outputs. The idea is discrete analog outputs based on a user-specified threshold for each range of concentration.

We did the following:

Mutagenesis of pBAD promoter sequence to create a stronger promoter (Strong pBAD) and a weaker promoter (Weak pBAD).
Quantification of mutant promoter-driven RFP fluorescence.
BioBrick submission.

pBAD Mutagenesis

A diagram of the changed nucleotide sequences of arabinose-inducible promoters. Green nucleotides of the wildtype show all sequences that were mutated from the wild type to form strong and weak.

Above is a sequence alignment of our promoter variants with the wild type pBAD, truncated for space. For the full sequences, see our pBAD strong [http://partsregistry.org/wiki/index.php?title=Part:BBa_K206000 BBa_K206000] and pBAD weak [http://partsregistry.org/wiki/index.php?title=Part:BBa_K206001 BBa_K206001].

Quantification

We assembled each promoter with the RFP reporter part I13507 in order to test the relative activity of the mutated promoters

We have been able to successfully show that at low arabinose concentrations, the activity of the Strong pBAD promoter and Weak pBAD promoter following arabinose induction is, as expected, greater and lesser respectively then the Wild Type pBAD promoter. By examining the development of a RFP reporter, it is observed that the Strong pBAD promoter has both a faster rate of development and reaches a higher maximum value compared to the Wild Type sequence. Similarly, the Weak pBAD promoter develops slower and to a lower maximum intensity. Additionally, we have shown that Strong pBAD and Weak pBAD are more and less responsive respectively to lower concentrations of arabinose then the Wild Type promoter. Therefore, they could be suitable to be used in conjunction as a bio-sensor.

BioBrick Submission

Here you can find our pBAD strong [http://partsregistry.org/wiki/index.php?title=Part:BBa_K206000 BBa_K206000] and pBAD weak [http://partsregistry.org/wiki/index.php?title=Part:BBa_K206001 BBa_K206001].

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-Above is a sequence alignment of our promoter variants with the wild type pBAD, truncated for space. For the full sequences, see our parts in the registry at <partinfo>K206000</partinfo> (strong) and <partinfo>K206001</partinfo> (weak).
+Above is a sequence alignment of our promoter variants with the wild type pBAD, truncated for space. For the full sequences, see our pBAD strong [http://partsregistry.org/wiki/index.php?title=Part:BBa_K206000 BBa_K206000] and pBAD weak [http://partsregistry.org/wiki/index.php?title=Part:BBa_K206001 BBa_K206001].
 ==Quantification==

Team:British Columbia/pBAD

From 2009.igem.org