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

Area of Science:

• Microbiology
• Bacterial Pathogenesis
• Evolutionary Biology

Background:

• Bacterial pathogens require precise control of virulence genes for host survival.
• The global repressor H-NS (Heat-stable Nucleoid Structuring protein) is crucial for balancing virulence gene expression.
• H-NS repression is vital in non-inducing environments, but its role in inducing conditions and pathogen evolution is less understood.

Purpose of the Study:

• To investigate the role of H-NS-mediated repression in virulence gene activation and heterogeneity.
• To explore how H-NS influences pathogen evolution in virulence-inducing conditions.
• To examine the impact of reduced H-NS DNA-binding affinity on bacterial adaptation.

Main Methods:

• Utilized a *Salmonella* strain with reduced H-NS DNA-binding affinity.
• Assessed virulence gene expression in individual bacteria.
• Employed experimental evolution to study pathogen adaptation.

Main Results:

• Reduced H-NS repression increased the proportion of virulence gene-expressing cells, enhancing *in vitro* epithelial cell infection.
• H-NS genotype constrained adaptive mutations, with loss of virulence gene expression being a common fitness strategy.
• H-NS plays a role in regulating gene expression heterogeneity in inducing conditions.

Conclusions:

• H-NS-mediated repression regulates virulence gene heterogeneity in inducing environments.
• The evolutionary conservation of H-NS constrains bacterial adaptive strategies in intracellular-like settings.
• Understanding H-NS function is critical for controlling bacterial pathogenesis and evolution.