Hidden Complexity of Yeast Adaptation under Simple Evolutionary Conditions

Area of Science:

• Microbial evolution
• Quantitative biology
• Genetics

Background:

• Determining how adaptive mutations increase fitness is challenging.
• Fitness gains are often assumed to stem from increased exponential growth rates.

Purpose of the Study:

• To quantitatively assess fitness gains from adaptive mutations in microbial evolution experiments.
• To investigate the role of different growth phases (fermentation, respiration, stationary) in fitness.

Main Methods:

• Systematic variation of growth phase lengths in batch serial transfer experiments.
• Fitness measurement using barcode sequencing across thousands of evolved clones.
• High-resolution pairwise competition experiments for selected clones.

Main Results:

• Adaptive lineages gained modest benefits from fermentation.
• Highest fitness gains were primarily linked to time spent in respiration.
• Benefits accrued during respiration were realized as shorter lag phases in subsequent growth cycles.

Conclusions:

• Fitness gains can be accrued during non-division phases like respiration.
• The realization of fitness benefits can be delayed to the next growth cycle.
• Microbial adaptation exhibits complexities beyond simple increases in growth rate.