Conserved and reproducible bacterial communities associate with extraradical hyphae of arbuscular mycorrhizal fungi

Abstract

Extraradical hyphae (ERH) of arbuscular mycorrhizal fungi (AMF) extend from plant roots into the soil environment and interact with soil microbial communities. Evidence of positive and negative interactions between AMF and soil bacteria point to functionally important ERH-associated communities. To characterize communities associated with ERH and test controls on their establishment and composition, we utilized an in-growth core system containing a live soil–sand mixture that allowed manual extraction of ERH for 16S rRNA gene amplicon profiling. Across experiments and soils, consistent enrichment of members of the Betaproteobacteriales, Myxococcales, Fibrobacterales, Cytophagales, Chloroflexales, and Cellvibrionales was observed on ERH samples, while variation among samples from different soils was observed primarily at lower taxonomic ranks. The ERH-associated community was conserved between two fungal species assayed, Glomus versiforme and Rhizophagus irregularis, though R. irregularis exerted a stronger selection and showed greater enrichment for taxa in the Alphaproteobacteria and Gammaproteobacteria. A distinct community established within 14 days of hyphal access to the soil, while temporal patterns of establishment and turnover varied between taxonomic groups. Identification of a conserved ERH-associated community is consistent with the concept of an AMF microbiome and can aid the characterization of facilitative and antagonistic interactions influencing the plant-fungal symbiosis.

Linking root exudation to belowground economic traits for resource acquisition

“…These exudates trigger a cascade of feedback loops among host plants, mycorrhizal fungi, and associated microbes around the hyphae (Jansa et al, 2013;Gorka et al, 2019;Jiang et al, 2021). In the case of arbuscular mycorrhizal fungi, hyphal exudates have pronounced effects on the growth and community of soil bacteria (Scheublin et al, 2010;Emmett et al, 2021) and induced positive interactions between arbuscular mycorrhizal fungi and specific bacteria contribute to soil nutrient transformation and turnover (including N and P) in the hyphosphere (Nuccio et al, 2013;Zhang et al, 2018). However, the mechanisms explaining how hyphal exudates recruit a functionally specific microflora, and to what extent host plants control these processes, remain poorly understood.…”

Bread Wheat (Triticum aestivum) Responses to Arbuscular Mycorrhizae Inoculation under Drought Stress Conditions

“…Inoculation with AM enhanced the water absorption in many of the plants that were subjected to drought stress. AM fungus mycelia can penetrate a larger volume of soil than the host plant roots, therefore increasing water absorption and transport to the roots and other plant parts, resulting in reduced drought stress [ 24 ]. Inoculation with the AM fungus significantly influenced morphological traits, increasing mostly leaf and tiller number per plant.…”

Possible role of arbuscular mycorrhizal fungi and associated bacteria in the recruitment of endophytic bacterial communities by plant roots

“…Rhizophagus irregularis), of which 12 showed phosphate-solubilizing activity (Sharma et al 2020). A distinct bacterial community closely associated with extraradical hyphae of Glomus versiforme, and conserved across divergent soils, was mainly represented by Proteobacteria (50% relative abundance), Actinobacteria (10%), Chloroflexi (9%), Acidobacteria (7%), Bacteroidetes (6%), and Fibrobacteres (4%) (Emmett et al 2021). An in vivo study reported, for the first time, that AMF hyphae may act as "transport agents" or "highways" for bacteria.…”