Thermally adapted Escherichia coli keeps transcriptomic response during temperature upshift exposure

Area of Science:

• Microbiology
• Molecular Biology
• Biotechnology

Background:

• The heat shock response is crucial for bacterial survival during temperature upshifts.
• Understanding thermal adaptation in Escherichia coli is vital for industrial applications.
• Previous studies focused less on the long-term evolutionary effects on heat shock response.

Purpose of the Study:

• To investigate the physiological and transcriptional responses to temperature upshift in a thermally evolved E. coli strain.
• To analyze the genetic basis of thermal adaptation in a D-lactic acid-producing E. coli.
• To assess the impact of adaptation on fermentation performance at elevated temperatures.

Main Methods:

• Adaptive laboratory evolution of a metabolically engineered E. coli strain (JU15) at 45°C.
• Continuous culture to study early and late responses to temperature upshift.
• Genomic sequencing to identify mutations in the evolved strain (ECL45).
• Transcriptomic analysis to compare gene expression between evolved and parental strains.

Main Results:

• The evolved strain ECL45 adapted to 45°C, maintaining high D-lactic acid production and substrate yield.
• Genomic analysis revealed eight mutations, including a double point mutation in the spoT gene.
• Transcriptomic data indicated a controlled stringent response contributing to thermal adaptation.
• Supplementation with hydrolyzed protein (0.15 g/L) enhanced thermal adaptation.

Conclusions:

• Thermal evolution in E. coli involves a controlled stringent response, facilitating growth at high temperatures.
• The spoT gene and its regulation play a significant role in thermotolerance.
• The adapted strain demonstrates potential for robust industrial fermentation processes at elevated temperatures.