Effective polyploidy causes phenotypic delay and influences bacterial evolvability.

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• The delay between bacterial mutation and phenotypic expression was historically debated but lacked evidence.
• Phenotypic delay in bacteria is generally assumed to be negligible, despite insufficient direct evidence.
• This assumption overlooks the potential impact on understanding bacterial evolution and adaptation.

Purpose of the Study:

• To investigate the existence and extent of phenotypic delay in bacterial mutations.
• To identify the underlying mechanisms causing phenotypic delay.
• To explore the consequences of phenotypic delay and effective polyploidy on mutation rate estimation and bacterial evolvability.

Main Methods:

• Utilized recombineering to introduce antibiotic resistance mutations into E. coli at specific time points.
• Tracked the expression of mutant phenotypes over time to quantify phenotypic delay.
• Employed modeling and simulation methods to analyze the impact of effective polyploidy on mutation rate estimation and evolutionary dynamics.

Main Results:

• Discovered a substantial median phenotypic delay of three to four generations for bacterial mutations.
• Identified multifork replication leading to effective polyploidy as the primary cause of this delay.
• Demonstrated that while per-copy mutation rates are accurately estimated, per-cell rates are not, and effective polyploidy influences the standing genetic variation and adaptive potential.

Conclusions:

• Phenotypic delay and effective polyploidy are crucial, previously overlooked factors in bacterial evolvability.
• These phenomena significantly impact the evolution of antibiotic resistance.
• Understanding phenotypic delay is essential for accurate bacterial mutation rate estimations and predicting evolutionary trajectories.