The underappreciated role for phase variation and quasi-clonality in microbial populations.

Phase variation in bacteria generates heritable phenotypic variants that persist across generations, producing quasi-clonal populations even when starting from a single bacterium.

• Why it matters: The contribution of phase variation to phenotypic heterogeneity is often overlooked, and the term is frequently absent when describing this kind of reversible, heritable diversification.
• What they did: The work synthesizes known mechanisms, including repeat-sequence variation, DNA inversions via site-specific recombination, reversible insertions/deletions, and switching between alternative methylation states.
• The result: Recognizing phase variation as a driver of quasi-clonality helps explain how stable heterogeneity can arise within microbial populations, improving how these processes are described.

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