Development of a native Escherichia coli induction system for ionic liquid tolerance.

Area of Science:

• Biotechnology
• Synthetic Biology
• Microbial Engineering

Background:

• Ionic liquids (ILs) are effective for lignocellulose pretreatment in biofuel production.
• Residual ILs in biomass hydrolysates inhibit microorganism growth and function.
• Heterologous expression of the eilA gene in E. coli can confer tolerance to ILs.

Purpose of the Study:

• To identify native E. coli IL-inducible promoters for regulating eilA gene expression.
• To develop novel control systems for enhancing microbial tolerance to ILs.
• To compare the efficacy of native promoters against an IPTG-inducible system.

Main Methods:

• Microarray analysis to identify IL-inducible promoters.
• Engineering E. coli strains with eilA under control of candidate promoters (PmarR', PydfO', PydfA').
• Comparison with PlacUV5 IPTG-inducible system.
• Selected-reaction monitoring mass spectrometry for protein quantification.
• Pooled culture competition assays to assess strain fitness.

Main Results:

• Native promoters PydfA' and PmarR' effectively rescued E. coli from IL toxicity, comparable to PlacUV5.
• Mechanistic model indicated inducible systems reduce gene expression at low IL levels.
• PydfA' and PmarR' significantly elevated EilA protein levels at high IL concentrations.
• The pPmarR'-eilA strain demonstrated superior fitness and outcompeted other strains at IL concentrations >150 mM.

Conclusions:

• Native E. coli promoters, particularly PmarR', can effectively regulate heterologous gene expression for IL tolerance.
• These native systems eliminate the need for IPTG induction, simplifying strain development.
• The findings facilitate the creation of industrially robust microbial strains for biofuel production.