Whole-cell
biosensors have attracted considerable interests because
they are robust, eco-friendly, and cost-effective. However, most of
the biosensors harness the naturally occurring wild-type promoter,
which often suffers from high background noise and low sensitivity.
In this study, we demonstrate how to design the core elements (i.e.,
RNA polymerase binding site and transcription factor binding site)
of the promoters to obtain a significant gain in the signal-to-noise
output ratio of the whole-cell biosensor circuits. As a proof of concept,
we modified the arsenite-regulated promoter from Escherichia
coli K-12 genome, such that it has a lower background and
higher expression. This was achieved by balancing the relationship
between the number of ArsR binding sites (ABS) and the activity of
the promoter and adjusting the location of the auxiliary ABS. A promoter
variant ParsD-ABS-8 was obtained with an induction ratio of 179 (11-fold
increase over the wild-type promoter) when induced with 1 μM
arsenite. Importantly, the developed biosensor exhibited good dose–response
in the range of 0.1 to 4 μM (R
2 =
0.9928) of arsenite with a detection limit of ca. 10 nM. These results
indicated that the engineered promoter modification approach could
be used to improve the performance of whole-cell biosensors, thereby
facilitating their practical application.
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