Friman Ville-Petri, Buckling Angus
1] Department of Zoology, University of Oxford, Oxford, UK [2] Department of Biosciences, Center for Ecology and Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Penryn, UK [3] Division of Ecology and Evolution, Imperial College London - Silwood Park Campus, Ascot, Berkshire, UK.
Department of Biosciences, Center for Ecology and Conservation, School of Biosciences, University of Exeter, Cornwall Campus, Penryn, UK.
ISME J. 2014 Sep;8(9):1820-30. doi: 10.1038/ismej.2014.40. Epub 2014 Mar 27.
The coincidental theory of virulence predicts that bacterial pathogenicity could be a by-product of selection by natural enemies in environmental reservoirs. However, current results are ambiguous and the simultaneous impact of multiple ubiquitous enemies, protists and phages on virulence evolution has not been investigated previously. Here we tested experimentally how Tetrahymena thermophila protist predation and PNM phage parasitism (bacteria-specific virus) alone and together affect the evolution of Pseudomonas aeruginosa PAO1 virulence, measured in wax moth larvae. Protist predation selected for small colony types, both in the absence and presence of phage, which showed decreased edibility to protists, reduced growth in the absence of enemies and attenuated virulence. Although phage selection alone did not affect the bacterial phenotype, it weakened protist-driven antipredatory defence (biofilm formation), its associated pleiotropic growth cost and the correlated reduction in virulence. These results suggest that protist selection can be a strong coincidental driver of attenuated bacterial virulence, and that phages can constrain this effect owing to effects on population dynamics and conflicting selection pressures. Attempting to define causal links such as these might help us to predict the cold and hot spots of coincidental virulence evolution on the basis of microbial community composition of environmental reservoirs.
毒力的巧合理论预测，细菌致病性可能是环境宿主中自然天敌选择的副产品。然而，目前的结果并不明确，而且多种普遍存在的天敌（原生生物和噬菌体）对毒力进化的同时影响此前尚未得到研究。在这里，我们通过实验测试了嗜热四膜虫原生生物捕食和PNM噬菌体寄生（细菌特异性病毒）单独以及共同作用如何影响铜绿假单胞菌PAO1毒力的进化，毒力通过蜡螟幼虫进行测定。在有无噬菌体的情况下，原生生物捕食都选择了小菌落类型，这些小菌落类型对原生生物的可食性降低，在没有天敌时生长减缓，毒力减弱。虽然单独的噬菌体选择不会影响细菌表型，但它削弱了原生生物驱动的反捕食防御（生物膜形成）、其相关的多效性生长成本以及毒力的相应降低。这些结果表明，原生生物选择可能是细菌毒力减弱的一个强大巧合驱动因素，并且噬菌体由于对种群动态的影响和相互冲突的选择压力而可以限制这种效应。试图定义诸如此类的因果关系可能有助于我们根据环境宿主的微生物群落组成来预测巧合毒力进化的热点和冷点。
