An Iterative, Synthetic Approach To Engineer a High-Performance PhoB-Specific Reporter

Area of Science:

• Microbiology and Molecular Biology
• Synthetic Biology
• Genomics

Background:

• Transcriptional reporters are vital for studying gene transcription and regulator activity.
• Native promoters often lack optimal characteristics for precise regulator activity readout.
• Synthetic promoters offer a solution but predictive design remains challenging.

Purpose of the Study:

• To synthesize an optimized transcriptional reporter for assessing PhoB activity.
• To achieve maximal 'on' expression, minimal 'off' background, and regulator specificity.
• To overcome limitations in predictive synthetic promoter design through iterative engineering.

Main Methods:

• Designed synthetic promoter sequences with randomized intervening nucleotides around PhoB-binding sites.
• Screened 83 constructs in *Vibrio fischeri* to identify bases correlating with expression levels.
• Performed a second round of rational design, followed by testing with green fluorescent protein (GFP) reporters.

Main Results:

• Identified specific nucleotide bases that enhance PhoB-dependent 'on' and 'off' expression.
• Developed a reporter with high PhoB-dependent expression and negligible background.
• Demonstrated reporter utility in *V. fischeri* culture, during symbiotic colonization, and in other *Proteobacteria*.

Conclusions:

• Iterative screening and reengineering can overcome challenges in synthetic promoter design.
• The developed reporter accurately reflects PhoB activity and phosphate availability.
• This promoter engineering strategy can be applied to create other regulator-specific reporters.