Bacterial community in the hyphosphere of an arbuscular mycorrhizal fungus differs from that in the surrounding environment and is influenced by hyphal disruption.

Abstract

Bacterial composition and functions in the hyphosphere of arbuscular mycorrhizal (AM) fungi are complex because AM fungal hyphae transport carbon compounds from plant photosynthesis which feed bacteria and act as signaling molecules. This function is lost when hyphae separate from roots, a common occurrence in soil. However, the impact of such disturbances on hyphal surface bacteria remains unclear. We used in vitro bi-compartmented Petri plates with carrot roots and the AM fungus Rhizophagus irregularis MUCL 43194, separating root and hyphal compartments. Treatments included hyphae connected to roots (+ AM), no hyphae (-AM), and hyphae cut at different times (C3D and C0D, where C3D indicates hyphae cut 3 days before inoculation and C0D indicates hyphae cut on the day of inoculation) subjected to a bacterial suspension extracted from a field soil. Thirteen bacterial phyla were identified, with Streptomyces, Pseudomonas, Rhodococcus, and Cellulomonas dominating. Hyphae increased bacterial ASV relative abundance, notably enriching Actinobacteria ASVs. After 14 days, α-diversity decreased from -AM to C3D, C0D, and + AM, with fewer Bacteroidetes species in + AM compared to -AM. Root-connected hyphae led to deterministic bacterial assembly, while cut hyphae resulted in stochastic assembly. Our findings show that physical disruption of hyphae significantly affects bacterial diversity and may influence ecological functions.