Data from: The basis of antagonistic pleiotropy in hfq mutations that have opposite effects on fitness at slow and fast growth rates

Mutations beneficial in one environment may cause costs in different environments, resulting in antagonistic pleiotropy. Here we describe a novel form of antagonistic pleiotropy that operates even within the same environment, where benefits and deleterious effects exhibit themselves at different growth rates. The fitness of hfq mutations in Escherichia coli affecting the RNA chaperone involved in small-RNA regulation is remarkably sensitive to growth rate. E. coli populations evolving in chemostats under nutrient limitation acquired beneficial mutations in hfq during slow growth (0.1 h-1) but not in populations growing 6-fold faster. Four identified hfq alleles from parallel populations were beneficial at 0.1 h-1 and deleterious at 0.6 h-1. The hfq mutations were beneficial, deleterious or neutral at an intermediate growth rate (0.5 h-1) and one changed from beneficial to deleterious within a 36 min difference in doubling time. The benefit of hfq mutations was due t o the greater transport of limiting nutrient, which diminished at higher growth rates. The deleterious effects of hfq mutations at 0.6 h-1 were less clear, with decreased viability a contributing factor. The results demonstrate distinct pleiotropy characteristics in the alleles of the same gene, probably because the altered residues in Hfq affected the regulation of expression of different genes in distinct ways. In addition, these results point to a source of variation in experimental measurement of the selective advantage of a mutation; estimates of fitness need to consider variation in growth rate impacting on the magnitude of the benefit of mutations and on their fitness distributions.

在某一环境中有益的突变，可能在不同环境中引发适应性代价，由此产生拮抗多效性（antagonistic pleiotropy）。本文报道了一种全新的拮抗多效性形式，其甚至可在同一环境内发挥作用——此时有益与有害效应会在不同生长速率下显现。涉及小RNA调控的RNA分子伴侣（RNA chaperone）的大肠杆菌（Escherichia coli）hfq基因突变的适合度，对生长速率极为敏感。在恒化器（chemostat）中处于营养限制条件下演化的大肠杆菌种群，在慢速生长（0.1 h⁻¹）时获得了hfq基因的有益突变，但在生长速率快6倍的种群中则未出现此类突变。从平行演化种群中鉴定出的4种hfq等位基因，在0.1 h⁻¹时表现为有益突变，在0.6 h⁻¹时则为有害突变。在中等生长速率（0.5 h⁻¹）下，hfq突变分别表现为有益、有害或中性；且有1种等位基因的效应在倍增时间相差36分钟的范围内，从有益转为有害。hfq突变的有益效应源于其对限制性营养物质的转运能力增强，而这一优势在更高生长速率下会逐渐减弱。hfq突变在0.6 h⁻¹时的有害效应机制尚未完全阐明，存活率下降是其中一个相关影响因素。本研究结果表明，同一基因的不同等位基因具有迥异的多效性特征，这可能是因为Hfq蛋白中发生改变的残基，以不同方式调控了不同基因的表达。此外，本研究结果提示，在实验测量突变的选择优势时存在变异来源：适合度评估需要考虑生长速率的差异，其会影响突变有益效应的强度以及适合度分布的特征。