Cooperative Institute for Research in Environmental Sciences, University of Colorado Boulder, Boulder, Colorado, USA.
Department of Molecular and Cellular Biology, University of Connecticut, Storrs, Connecticut, USA.
Appl Environ Microbiol. 2024 Apr 17;90(4):e0201123. doi: 10.1128/aem.02011-23. Epub 2024 Mar 27.
Soil protists have been shown to contribute to the structure and function of the rhizosphere in a variety of ways. Protists are key contributors to nutrient cycling through the microbial loop, where biomass is digested by protists and otherwise stored nutrients are returned to the environment. Protists have also been shown to feed on plant pathogenic bacteria and alter root microbiomes in ways that may benefit plants. Recently, a mechanism involving bacterial transport, facilitated by protists, has been hypothesized to contribute to the spatial distribution of bacteria in the rhizosphere. Here, we observe the differential abilities of three soil protists: a ciliate ( sp.), a flagellate ( sp.), and a naked amoeba () to transport nitrogen-fixing to infectible root tips. Co-inoculation of protists plus resulted in the movement of bacteria, as measured by the presence of nitrogen-fixing nodules, up to 15 cm farther down the root systems when compared to plants inoculated with alone. Co-inoculation of the ciliate sp., with , resulted in shoot weights that were similar to plants that grew in nitrogen-replete potting mix. sp.-feeding style and motility likely contributed to their success at transporting bacteria through the rhizosphere. We observed that the addition of protists alone without the co-inoculum of resulted in plants with larger shoot weights than control plants. Follow-up experiments showed that protists plus their associated microbiomes were aiding in plant health, likely through means of nutrient cycling.IMPORTANCEProtists represent a significant portion of the rhizosphere microbiome and have been shown to contribute to plant health, yet they are understudied compared to their bacterial and fungal counterparts. This study elucidates their role in the rhizosphere community and suggests a mechanism by which protists can be used to move bacteria along plant roots. We found that the co-inoculation of protists with nitrogen-fixing beneficial bacteria, , resulted in nodules farther down the roots when compared to plants inoculated with S. alone, and shoot weights similar to plants that received nitrogen fertilizer. These data illustrate the ability of protists to transport viable bacteria to uninhabited regions of the root system.
土壤原生动物已被证明以多种方式促进根际的结构和功能。原生动物是通过微生物环进行养分循环的关键贡献者，其中生物量被原生动物消化，否则储存的养分被返回环境。原生动物也被证明可以捕食植物病原菌，并以可能有益于植物的方式改变根微生物组。最近，一种涉及细菌运输的机制，由原生动物促成，被假设有助于细菌在根际中的空间分布。在这里，我们观察了三种土壤原生动物的不同能力：纤毛虫（sp.）、鞭毛虫（sp.）和裸变形虫（），它们能够将固氮细菌运输到可感染的根尖。与单独接种 相比，将原生动物与 共同接种会导致细菌的运动，这可以通过存在固氮结瘤来衡量，细菌可以沿着根系向下移动长达 15 厘米。与在富含氮的盆栽混合中生长的植物相比，纤毛虫 sp.与 共同接种导致的地上部重量相似。原生动物 sp.的摄食方式和运动能力可能有助于它们成功地将细菌运输穿过根际。我们观察到，单独添加原生动物而不添加 的共接种物会导致地上部重量大于对照植物。后续实验表明，原生动物及其相关微生物组有助于植物健康，可能通过养分循环的方式。
重要性
原生动物是根际微生物组的重要组成部分，已被证明有助于植物健康，但与细菌和真菌相比，它们的研究还不够充分。本研究阐明了它们在根际群落中的作用，并提出了一种原生动物可以用来将细菌沿植物根系移动的机制。我们发现，与固氮有益细菌 共同接种原生动物会导致根上的结瘤比单独接种 S. 时更远，地上部重量与接受氮肥的植物相似。这些数据说明了原生动物将有活力的细菌运送到根系未居住区域的能力。
