Data from: Coexistence of evolving bacteria stabilized by a shared Black Queen function

The Black Queen Hypothesis (BQH) was originally proposed to explain the dependence of some marine bacteria on helper organisms for protection from hydrogen peroxide (HOOH). The BQH predicts that selection for the evolutionary loss of leaky functions from individuals can produce commensal or mutualistic interactions. We demonstrated the leakiness of HOOH detoxification by complementing a HOOH-sensitive Escherichia coli mutant with a plasmid-encoded HOOH-detoxifying enzyme, KatG, and then evolving populations founded by this strain in two environments. When HOOH was absent, plasmid-carrying cells were outcompeted by plasmid-free segregants, reflecting the high cost of KatG expression. However, plasmid-carrying and plasmid-free cells coexisted for at least 1,200 generations in three replicate populations evolved in the presence of HOOH, although their relative proportions fluctuated as beneficial mutations arose in one type or the other. Evolved plasmid-bearing cells reduced the cost of plasmid carriage even as they increased the rate of HOOH removal relative to the ancestor. Meanwhile, plasmid-free cells remained dependent on HOOH detoxification by the plasmid-bearing cells. These results demonstrate that partitioning of a Black Queen function can enable the stable coexistence of very similar organisms, even in this most restrictive case where the two types are competing for a single resource.黑皇后假说（Black Queen Hypothesis, BQH）最初被提出，用于解释部分海洋细菌依赖辅助生物以抵御过氧化氢（hydrogen peroxide, HOOH）的现象。该假说预测，对个体渗漏性功能的进化缺失进行选择，可产生偏利共生或互利共生关系。本研究通过向过氧化氢敏感型大肠杆菌（Escherichia coli）突变株导入质粒编码的过氧化氢解毒酶KatG，并将以该菌株为起始构建的种群在两种环境中开展演化实验，证实了过氧化氢解毒功能的渗漏性。当无过氧化氢存在时，携带质粒的细胞会被无质粒的分离株竞争淘汰，这反映了KatG表达的高代谢成本。然而，在三种添加过氧化氢的重复演化种群中，携带质粒与无质粒的细胞至少共存了1200代，尽管二者的相对比例会因其中一类细胞出现有益突变而发生波动。相较于祖先菌株，演化获得的携带质粒细胞不仅提升了过氧化氢清除速率，同时降低了携带质粒的代谢成本。与此同时，无质粒细胞仍依赖携带质粒细胞完成过氧化氢解毒过程。本研究结果表明，黑皇后功能的分工可实现高度相似的生物种群稳定共存，即便在两类细胞竞争单一资源这一最严苛的实验场景中亦是如此。