Medicago root nodule microbiomes: insights into a complex ecosystem with potential candidates for plant growth promotion

Abstract

microbes within and upon them. We analyzed the microbiomes of these underground organs from both an important crop plant (Medicago sativa) and a related legume (M. polymorpha) using metagenomic and culture-based techniques to identify the main cultivatable contributors to plant growth enhancement. Methods Using high-throughput sequencing, culturing, and in planta techniques, we identified and analyzed a broad population of the bacterial taxa within Medicago nodules and the surrounding soil. Results Fifty-one distinct bacterial strains were isolated and characterized from nodules of both Medicago

Back to the future: Using herbarium specimens to isolate nodule‐associated bacteria

“…Further work should compare historic and contemporary nodule microbiomes of Medicago lupulina to determine the occurrence of taxa found in our collection in contemporary populations. Interestingly the number of genera we were able to recover is similar to the number of genera recovered in other nodule microbiome culturing work of both Medicago lupulina (14 genera, C. Chang personal communication, March 28, 2024) and other Medicago species (10 genera, Martínez‐Hidalgo et al., 2022 ).…”

“…Nodule forming Microvirga form nodules in several legume species, including Listia , Lupinus (Ardley et al., 2012 , 2013 ), and Vigna (Radl et al., 2014 ). Microvirga has not been described on Medicago lupulina but has been found in association with Medicago sativa nodules (Ilyas et al., 2022 ; Li et al., 2018 ) and the order Hyphomicrobiales is found in Medicago polymorpha nodules (Martínez‐Hidalgo et al., 2022 ). Additionally, 11 Microvirga OTUs were identified on Medicago truncatula nodules (Brown et al., 2020 ).…”

“…Besides the main nodule‐forming rhizobia species, nodules are often colonized by a diversity of other bacteria. Work in related Medicago species revealed taxa from at least 10 bacterial genera colonizing nodules (Martínez‐Hidalgo et al., 2022 ). Understanding nodule‐associated bacteria is important because they can perform important functions in the rhizosphere critical to plant development, growth, and the functioning of the legume rhizobia symbiosis.…”

Bambara Nut Root-Nodules Bacteria from a Semi-Arid Region of South Africa and Their Plant Growth-Promoting Traits

“…Te plant microbiome determines plant health and productivity. Te phytomicrobiome contains a wide variety of bacterial and fungal microorganisms that colonize all parts of the plant, particularly the roots [7]. Tese organisms transform essential nutrients into useable forms that can be assimilated by plants while plants release a variety of chemical substances into the rhizosphere, called exudates, which mediate the interaction between plants and microbes [8,9].…”

“…Te recent advancements in undersatanding the mechanisms emplyoyed by phytomicrobiome in stimulating plant growth and development are expected to continue to increase [10]. A paraphyletic genus of bacteria known as rhizobia within plant tissues transforms atmospheric nitrogen to ammonia by the highly specialized microbial community found in the root nodules of leguminous plants [7]. Rhizobia difer in how they approach nodulation.…”