EVOLUTIONARY ADAPTATION TO TEMPERATURE II. THERMAL NICHES OF EXPERIMENTAL LINES OF ESCHERICHIA COLI.

Area of Science:

• Evolutionary biology
• Microbiology
• Genomics

Background:

• Bacterial adaptation is crucial for survival in changing environments.
• Understanding thermal adaptation in Escherichia coli provides insights into microbial evolution.

Purpose of the Study:

• To investigate the impact of long-term temperature selection on the thermal niche and fitness of Escherichia coli.
• To determine if adaptation to specific temperatures alters the overall thermal tolerance or optima.

Main Methods:

• Propagating Escherichia coli in controlled temperature environments (constant 32, 37, 42°C, or alternating 32/42°C) for 2,000 generations.
• Assessing thermal niche limits (survival range) and relative fitness across a temperature gradient (12-44°C).
• Comparing evolved lines to their common ancestor to quantify fitness changes.

Main Results:

• Thermal niche limits (lower and upper bounds) were unaffected by selection history, remaining around 19°C and 42°C.
• Mean fitness increases were temperature-specific, with optima shifting towards the selected temperature.
• Significant divergence in thermal optima (up to 10°C) was observed between groups selected at different constant temperatures.
• Tradeoffs in fitness at other temperatures were minimal and not consistently observed.

Conclusions:

• Adaptation in Escherichia coli is highly temperature-specific.
• Divergence in thermal optima did not significantly impact the overall thermal niche boundaries.
• Fitness improvements at specific temperatures did not necessarily lead to widespread fitness decrements across the thermal range.