The pH of the mouth drops several times per day after mealtimes, resulting in severe tooth decay over time if not addressed. One way to combat this problem is to engineer the microbiome of the mouth to respond dynamically to changes in pH. To enable this, here we present the development of a novel dual-state promoter for the detection of and response to pH fluctuations in the mouth.

This novel transcriptional regulation element will be capable of having both constitutive and inducible activity. This is achieved by linking a constitutive promoter downstream a pH-inducible promoter. We plan to characterize our dual-state promoter by first linking single promoters upstream green fluorescent protein (GFP) and assess the transcriptional activity via fluorescence assays. This will be followed by fluorescence assays on the dual-state promoter.

From the construction of a dual-state promoter, we hypothesize three outcomes:

• The pH-inducible promoters will demonstrate minimal activity at a neutral pH, with an intense activity as the pH nears and crossed the cavity formation threshold, at pH 5.5
• The constitutive promoters will have a constant activity, independent of pH.
• The dual-state promoter construct will exhibit the combined effect of both promoters, performing at a constant basal expression as well as at an elevated level when prompted with a drop in pH.

This technology should have future applications in any system requiring pH detection and response.