Perturbing H-NS function reveals roles in restricting virulence heterogeneity and pathogen adaptation

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Genomics

Background:

• Histone-like nucleoid structuring protein (H-NS) silences horizontally acquired genes in bacteria, balancing expression costs.
• Pathogenic bacteria like Salmonella Typhimurium (STm) utilize H-NS to manage costly virulence regulons for host survival.
• Understanding how partial H-NS dysfunction affects STm virulence heterogeneity and adaptation is crucial.

Purpose of the Study:

• To investigate the impact of a reduced H-NS DNA-binding affinity (hypomorph) on STm virulence gene expression and host cell infection.
• To explore how H-NS hypomorph impacts STm adaptation during experimental evolution in intracellular-like conditions.
• To elucidate the role of H-NS in setting single-cell virulence activation thresholds and its function as an evolutionary buffer.

Main Methods:

• Identification and characterization of an STm hns hypomorph strain with reduced H-NS DNA-binding affinity.
• In vitro assessment of epithelial cell infection rates by wild-type and mutant strains.
• Experimental evolution of STm populations under intracellular-like conditions to study adaptive mutations.

Main Results:

• The STm hns hypomorph strain exhibited increased proportions of virulence-expressing cells, leading to enhanced in vitro epithelial cell infection.
• Both wild-type and mutant STm populations adapted by disrupting the SPI-2 virulence regulon.
• The mutant population acquired unique adaptive mutations to address dysregulated gene expression caused by H-NS impairment.

Conclusions:

• H-NS functions as a critical regulator of single-cell virulence activation thresholds in STm.
• Even minor disruptions to H-NS silencing significantly impact bacterial adaptation and virulence.
• H-NS acts as an evolutionary buffer, influencing how pathogens adapt to host environments.