Part:BBa_K5152004

PbrR-pPbr lead sensing chromoprotein reporter device

Our biosensor construct for detecting heavy metal lead is inspired by iGEM 2007 Team Brown (BBa_I721001). The regulatory protein PbrR controls the pPbr promoter. When lead is present, PbrR forms a dimer, activating the expression of downstream coding sequences.

We employed this construct in E. coli, which doesn't naturally express PbrR, so we co-expressed it. We used dTomato as the reporter gene, an RFP with chromoprotein properties, chosen for its visible color to avoid the need for expensive equipment. This sequence, optimized by our 2023 team, ensures vibrant and stable expression.

Our project examined the expression profiles of several chromoproteins, including amilCP, cjBlue, tsPurple, eforRed, and dTomato. For more details, please refer to our wiki page.

Usage and Biology

Lead Detection Functional Assay

Our biosensor effectively detected lead. After adding a final concentration of 100 µM lead (II) nitrate to the culture, cells exhibited visible red coloration in the pellet after 12 hours and significant culture coloration after 24 hours. We noted leaky expression with incubation times over 18 hours, suggesting a need to adjust the regulatory protein expression strength or incubation conditions.

Fig. 1: Biosensor cells exposed to 100 µM lead (II) nitrate showed an observable red color in the pellets. While there is a noticeable difference, the red coloration in the culture form is less obvious.

Fig. 2: After 24 hours of incubation, the red color in the liquid becomes visible. However, a slightly more pronounced red color is observed in cells without added lead, indicating leaky expression.

Concentration Dependent Signals

We tested the biosensors with varying lead concentrations (0.01 µM to 1000 µM). After 24 hours, color intensity was proportional to lead concentration, except at 500 µM and 1000 µM, likely due to toxicity affecting protein expression, as smaller pellet sizes were observed.

Fig. 3: The color intensity of the biosensor cells increases with higher lead concentrations, suggesting that the biosensor design is concentration-dependent.

Sequence and Features

Assembly Compatibility:

• 10
  COMPATIBLE WITH RFC[10]
• 12
  INCOMPATIBLE WITH RFC[12]

  Illegal NheI site found at 35
  Illegal NheI site found at 58
  
• 21
  COMPATIBLE WITH RFC[21]
• 23
  COMPATIBLE WITH RFC[23]
• 25
  COMPATIBLE WITH RFC[25]
• 1000
  INCOMPATIBLE WITH RFC[1000]

  Illegal SapI.rc site found at 714