Bacteria can form heterogeneous populations containing phenotypic variants of genetically identical cells. The heterogeneity of populations can be considered a bet-hedging strategy allowing adaptation to unknown environmental changes – at least some individual subpopulations or cells might be able to withstand future adverse conditions. Using Percoll gradient centrifugation, we demonstrated that in an Escherichia coli culture exposed to heat shock at 50 °C, two physiologically distinct subpopulations were formed. A high-density subpopulation (HD₅₀) demonstrated continued growth immediately after its transfer to LB medium, whereas the growth of a low-density subpopulation (LD₅₀) was considerably postponed. The LD₅₀ subpopulation contained mainly viable but non-culturable bacteria and exhibited higher tolerance to sublethal concentrations of antibiotics or H₂O₂ than HD₅₀ cells. The levels of aggregated proteins and main molecular chaperones were comparable in both subpopulations; however, a decreased number of ribosomes and a significant increase in protein oxidation were observed in the LD₅₀ subpopulation as compared with the HD₅₀ subpopulation. Interestingly, under anaerobic heat stress, the formation of the HD₅₀ subpopulation was decreased and culturability of the LD₅₀ subpopulation was significantly increased. In both subpopulations the level of protein aggregates formed under anaerobic and aerobic heat stress was comparable. We concluded that the formation of protein aggregates was independent of oxidative damage induced by heat stress, and that oxidative stress and not protein aggregation limited growth and caused loss of LD₅₀ culturability. Our results indicate that heat stress induces the formation of distinct subpopulations differing in their ability to grow under standard and stress conditions.

细菌可以形成异质性种群，其中包含遗传上相同的细胞的表型变异。群体的异质性可以被视为对冲策略，可以适应未知的环境变化-至少某些个体亚群或细胞可能能够承受未来的不利条件。使用Percoll梯度离心，我们证明了在暴露于50°C的热休克的大肠杆菌培养物中，形成了两个生理上不同的亚群。高密度亚群（HD ₅₀）转移到LB培养基后立即显示出持续的生长，而低密度亚群（LD ₅₀）的生长被大大推迟了。LD ₅₀亚群主要包含存活但不可培养的细菌，并且对亚致死浓度的抗生素或H ₂ O _2的耐受性高于HD ₅₀细胞。在这两个亚群中，聚集蛋白和主要分子伴侣的水平相当。然而，与HD ₅₀亚群相比，LD ₅₀亚群中核糖体数量减少，蛋白质氧化显着增加。有趣的是，在厌氧热胁迫下，HD ₅₀亚群的形成减少，LD _50的可培养性亚群显着增加。在两个亚群中，在厌氧和有氧热胁迫下形成的蛋白质聚集体的水平是可比的。我们得出的结论是，蛋白质聚集体的形成与热应激诱导的氧化损伤无关，并且氧化应激而不是蛋白质聚集体限制了生长，并导致了LD ₅₀可培养性的丧失。我们的结果表明，热胁迫诱导了不同亚群的形成，这些亚群在标准和胁迫条件下的生长能力不同。