Mutation rate dynamics reflect ecological change in an emerging zoonotic pathogen

Area of Science:

• Microbiology
• Evolutionary Biology
• Genetics

Background:

• Mutation rates vary significantly within and between bacterial species.
• Understanding the drivers of mutation rate variation is crucial for bacterial evolution.
• Ecology and genome size are hypothesized factors influencing mutation rates.

Purpose of the Study:

• To investigate the influence of ecology and genome size on mutation rates in Streptococcus suis.
• To compare mutation rates between tonsil carriage and invasive disease isolates of Streptococcus suis.
• To explore the relationship between pathogenicity, genome characteristics, and mutation bias.

Main Methods:

• Conducted mutation accumulation experiments on eight strains of Streptococcus suis.
• Compared mutation rates and mutation biases between different ecological isolates (carriage vs. invasive).
• Analyzed the correlation between mutation rate, genome size, and pathogenicity.

Main Results:

• Invasive disease isolates consistently evolved higher mutation rates than carriage isolates, irrespective of genome size.
• Isolates from more pathogenic populations exhibited a stronger G/C to A/T mutation bias.
• More pathogenic populations, often with smaller and AT-rich genomes, showed distinct mutation patterns.
• Ecology emerged as a stronger correlate of mutation rate than genome size.

Conclusions:

• Ecology is a primary driver of mutation rate variation in Streptococcus suis.
• Transition to invasive disease is associated with a rapid increase in mutation rate.
• Ecological factors significantly impact the adaptive potential of bacterial pathogens.