Living on the edge: emergence of spontaneous gac mutations in Pseudomonas protegens during swarming motility
Living on the edge: emergence of spontaneous gac mutations in Pseudomonas protegens during swarming motility
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DOI：
10.1111/1462-2920.13288
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发表时间：
2016-10-01
影响因子：
5.1
通讯作者：
Raaijmakers, Jos M.
中科院分区：
文献类型：
--
作者：
Song, Chunxu;Kidarsa, Teresa A.;Raaijmakers, Jos M.
群体运动是一种鞭毛驱动的多细胞行为，它允许细菌在新的生态位定居并逃避竞争。在这里，我们研究了假单胞菌蛋白Pf-5群体菌落中GacS/GacA双组分调控系统的特异性突变的进化。实验进化分析表明，野生型Pf-5的重复蜂群驱动了gacS/gacA自发突变体在蜂群边缘的积累。这些突变体不能自己聚集，因为它们缺乏生物表面活性剂orfamide A的生产，但它们可以与产生orfamide的野生型Pf-5共同聚集。这些共群实验进一步表明，DgacA突变细胞确实在边缘上占主导地位，并且初始DgacA与野生型的f-5比例至少为2:1会导致群体的崩溃。随后的全基因组转录组分析显示，在群体培养基中，DgacA突变体中与运动性、资源获取、趋化性和外排相关的基因显著上调。此外，透射电镜显示，DgacA突变体细胞比野生型细胞更长，鞭毛更多，这可能解释了它们在群体边缘的优势。我们假设，通过点突变的适应性进化是范围扩展微生物种群的共同特征，并且这些突变在细菌扩散到新区域期间的假定适应度效益是频率依赖的。
Swarming motility is a flagella-driven multicellular behaviour that allows bacteria to colonize new niches and escape competition. Here, we investigated the evolution of specific mutations in the GacS/GacA two-component regulatory system in swarming colonies of Pseudomonas protegens Pf-5. Experimental evolution assays showed that repeated rounds of swarming by wildtype Pf-5 drives the accumulation of gacS/gacA spontaneous mutants on the swarming edge. These mutants cannot swarm on their own because they lack production of the biosurfactant orfamide A, but they do co-swarm with orfamide-producing wildtype Pf-5. These co-swarming assays further demonstrated that DgacA mutant cells indeed predominate on the edge and that initial DgacA: wildtype Pf-5 ratios of at least 2: 1 lead to a collapse of the swarming colony. Subsequent whole-genome transcriptome analyses revealed that genes associated with motility, resource acquisition, chemotaxis and efflux were significantly upregulated in DgacA mutant on swarming medium. Moreover, transmission electron microscopy showed that DgacA mutant cells were longer and more flagellated than wildtype cells, which may explain their predominance on the swarming edge. We postulate that adaptive evolution through point mutations is a common feature of range-expanding microbial populations and that the putative fitness benefits of these mutations during dispersal of bacteria into new territories are frequency-dependent.