Many bacterial species generate phenotypically heterogeneous subpopulations as a strategy for ensuring the survival of the population as a whole – an environmental stress that eradicates one subpopulation may leave other phenotypic groups unharmed, allowing the lineage to continue. Phase variation, a process that functions as an ON/OFF switch for gene expression, is one way that bacteria achieve phenotypic heterogeneity. Phase variation occurs stochastically and reversibly, and in the presence of a selective pressure the advantageous phenotype(s) predominates in the population. Phase variation can occur through multiple genetic and epigenetic mechanisms. This review focuses on conservative site-specific recombination that generates reversible DNA inversions as a genetic mechanism mediating phase variation. Recent studies have sparked a renewed interest in phase variation mediated through DNA inversion, revealing a high level of complexity beyond simple ON/OFF switching, including unusual modes of gene regulation, and highlighting an underappreciation of the use of these mechanisms by bacteria.

许多细菌物种产生表型异质的亚群，作为确保整个种群生存的策略——根除一个亚群的环境压力可能会使其他表型群不受伤害，从而使谱系继续存在。相位变异是一个作为基因表达开/关开关的过程，是细菌实现表型异质性的一种方式。相位变化随机且可逆地发生，并且在存在选择压力的情况下，有利的表型在群体中占主导地位。相位变异可以通过多种遗传和表观遗传机制发生。本综述侧重于保守的位点特异性重组，该重组产生可逆的 DNA 倒位作为介导相变的遗传机制。