Data from: Broad thermal tolerance is negatively correlated with virulence in an opportunistic bacterial pathogen

Predicting the effects of global increase in temperatures on disease virulence is challenging, especially for environmental opportunistic bacteria, because pathogen fitness may be differentially affected by temperature within and outside host environment. So far, there is very little empirical evidence on the connections between optimal temperature range and virulence in environmentally growing pathogens. Here we explored if the virulence of an environmentally growing opportunistic fish pathogen, Flavobacterium columnare, is malleable to evolutionary changes via correlated selection on thermal tolerance. To this end, we experimentally quantified the thermal performance curves (TPCs) for maximum biomass of 49 F. columnare isolates from eight different geographic locations in Finland over ten years (2003-2012). We also characterized virulence profiles of these strains in a zebra-fish (Danio rerio) infection model. We show that virulence among the strains increased over the years, but tolerance to higher temperatures was negatively associated with virulence. Our data suggest that temperature has a strong effect on the pathogen genetic diversity, and therefore presumably also on disease dynamics. However, the observed increase in frequency and severity of F. columnare epidemics over the last decade cannot be directly linked to bacterial evolution due to increased mean temperature, but is most likely associated with factors related to increased length of growing season, or other time dependent change in environment. Our study demonstrates that complex interactions between the host, the pathogen and the environment influence disease virulence of environmentally growing opportunistic pathogen.预测全球升温对疾病毒力的影响颇具挑战，对于环境型机会致病菌而言更是如此，因为致病菌的适合度在宿主内外环境中受温度的影响存在差异。迄今为止，关于环境增殖型致病菌的最适温度范围与毒力之间关联的实证证据极为匮乏。本研究旨在探究：环境增殖型鱼类机会致病菌柱状黄杆菌（Flavobacterium columnare）的毒力是否可通过热耐受性的关联选择发生进化改变。为此，我们针对2003-2012年十年间从芬兰8个不同地理区域分离得到的49株柱状黄杆菌，实验测定了其最大生物量的热性能曲线（thermal performance curves, TPCs）。我们还在斑马鱼（Danio rerio）感染模型中表征了这些菌株的毒力谱。研究结果显示，各菌株的毒力随年份推移呈上升趋势，但高温耐受性与毒力呈负相关关系。我们的数据表明，温度对致病菌的遗传多样性具有显著影响，因此推测其对疾病动态同样存在作用。然而，近十年来观测到的柱状黄杆菌流行病频率与严重程度的上升，无法直接归因于平均温度升高带来的细菌进化，其更可能与生长季延长相关因素，或其他随时间变化的环境因素有关。本研究证实，宿主、致病菌与环境之间的复杂相互作用，会影响环境增殖型机会致病菌的疾病毒力。