Description

Quorum sensing is an organic chemical signal that regulates a variety of physiological activities of bacteria, such as cell movement, growth, and biofilm formation. This sensing mechanism is mediated by diffusible chemical signals called homoserine lactones. The concentration of signal molecules outside the cell increases with increasing cell density and the signal molecule itself is permeable to the cell membrane. Upon reaching the threshold concentration of the chemical signal, the quorum sensing system is activated to trigger expression or inhibition of the gene.

Design

We used the quorum sensing system of iron bacteria isolated from pipeline rust. This system is homologous to the LuxR system. The iron bacteria itself produces the AfeR protein, which binds to 3-oxo-C12-AHL and dimerizes. This dimer binds to afeR box and activates gene transcription. Therefore, the recognition of iron bacteria by Escherichia coli can be achieved by constructing a heterologous AfeR protein of iron bacteria and a corresponding activated promoter in engineered E. coli.

Result

Gene fragment of GFP is synthesized through Genescript and it is on vector pUC57.

The plasmid was transformed to E. coli DH5α and cultured at 37 °C for 12 h. Then positive bacteria is cultured in LB culture medium adding with 0.1% ampicillin. After bacteria grows to logarithmic phase, adding AHL until final concentration is 10-4 ,10-5,10-6 ,10-7,10-8, 10-9 mol/L. Then light absorption is measured. Excitation/Emission wavelength is 485nm/530nm.

When the AHL concentration is in the range of 10-7~10-8 mol/L, the fluorescence insensity was jump. When the AHL concentration is above 10-7 mol/L, the promoter will respond.

Reference

1. Mol Syst Biol. 2011; 7: 521. Engineering microbes to sense and eradicate Pseudomonas aeruginosa, a human pathogen Nazanin Saeidi,1,* Choon Kit Wong

2. Biological Research 2005 A Lux-like quorum sensing system in the extreme acidophile Acidithiobacillus ferrooxidans. Mariella O. Rivas, Michael Seeger

3.American Society for Microbiology Evidence for a Functional Quorum-Sensing Type AI-1 System in the Extremophilic Bacterium Acidithiobacillus ferrooxidans Carolina Farah1, Mario Vera