Recurrent mutualism breakdown events in a legume rhizobia metapopulation
Recurrent mutualism breakdown events in a legume rhizobia metapopulation
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DOI：
10.1098/rspb.2019.2549
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发表时间：
2020-01-29
影响因子：
4.7
通讯作者：
Sachs, Joel L.
中科院分区：
文献类型：
--
作者：
Gano-Cohen, Kelsey A.;Wendlandt, Camille E.;Sachs, Joel L.
细菌互利共生对真核生物产生重大的适应性益处，重塑宿主表型及其与环境的相互作用。然而，微生物互惠种群预计产生突变体，从提供昂贵的服务，主机，同时保持利用主机资源的能力缺陷。在这里，我们研究了共生固氮的共生服务在一个集合种群的根膨胀慢生根瘤菌属。与本地豆科植物糙伏毛蚁有关。从加州700 km的样带中收集了85个慢生根瘤菌菌株，对10个A. strigosus种群。我们将每个慢生根瘤菌菌株克隆接种到A. strigosus主机和量化的繁殖能力和感染的净效应，包括主机的增长和同位素氮浓度。来自五个种群的六株慢生根瘤菌被归类为无效，因为它们形成根瘤，但没有通过固氮增强宿主生长。另外6个来自3个种群的菌株未能形成根瘤。系统发育重建推断出两种类型的共生关系破坏，包括3 ~ 4种独立的有效性丧失和5种繁殖能力丧失。糙伏毛这些互利共生崩溃事件的进化和基因驱动因素仍然知之甚少。
Bacterial mutualists generate major fitness benefits for eukaryotes, reshaping the host phenotype and its interactions with the environment. Yet, microbial mutualist populations are predicted to generate mutants that defect from providing costly services to hosts while maintaining the capacity to exploit host resources. Here, we examined the mutualist service of symbiotic nitrogen fixation in a metapopulation of root-nodulating Bradyrhizobium spp. that associate with the native legume Acmispon strigosus. We quantified mutualism traits of 85 Bradyrhizobium isolates gathered from a 700 km transect in California spanning 10 sampled A. strigosus populations. We clonally inoculated each Bradyrhizobium isolate onto A. strigosus hosts and quantified nodulation capacity and net effects of infection, including host growth and isotopic nitrogen concentration. Six Bradyrhizobium isolates from five populations were categorized as ineffective because they formed nodules but did not enhance host growth via nitrogen fixation. Six additional isolates from three populations failed to form root nodules. Phylogenetic reconstruction inferred two types of mutualism breakdown, including three to four independent losses of effectiveness and five losses of nodulation capacity on A. strigosus. The evolutionary and genomic drivers of these mutualism breakdown events remain poorly understood.