Bacterial heterozygosity promotes survival under multidrug selection

Area of Science:

• Microbiology
• Genetics
• Evolutionary Biology

Background:

• Most bacteria possess a single chromosome, but some species are naturally polyploid with multiple chromosomes.
• Bacterial heterozygosity, arising from distinct chromosomes, is less understood than in eukaryotes.
• Antibiotic resistance presents a critical context for studying bacterial heterozygosity's impact on survival.

Purpose of the Study:

• To investigate the role of bacterial genomic heterozygosity in survival under antibiotic pressure.
• To compare the fitness costs and benefits of heterozygous versus homozygous antibiotic resistance in bacteria.

Main Methods:

• Utilized a cell-wall-deficient model system in Kitasatospora viridifaciens.
• Examined survival rates across various antibiotic concentrations in heterozygous and recombinant bacterial cells.
• Assessed fitness costs associated with constitutive resistance gene expression.

Main Results:

• Heterozygous cells with differing antibiotic resistance markers demonstrated broad survival across antibiotic concentrations.
• Recombinant cells with identical resistance genes on a single chromosome survived but incurred significant fitness costs.
• Heterozygous cells mitigated costs by adjusting chromosome ratios, enabling adaptive plasticity.

Conclusions:

• Bacterial heterozygosity enhances adaptive plasticity and survival in variable environments, akin to multicopy plasmids.
• Flexible chromosome ratio adjustment in heterozygous bacteria allows for rapid environmental responses.
• Genomic heterozygosity offers a survival advantage against antibiotics by balancing resistance and fitness costs.