Antarctic moss fairy rings serve as reservoirs for plant growth-promoting bacteria

Antarctic terrestrial vegetation and microbial communities are undergoing climate-driven changes, which in some cases have been linked to the emergence of plant diseases. Ring-shaped plant disease structures, known as fairy rings (FRs), have been observed in moss fields dominated by Sanionia uncinata. Previous studies suggest that FRs promote vegetation development through interactions with bacterial communities. This raises the possibility that the bacterial communities in Antarctic FRs may also have ecologically significant functions. To address this, we analyzed the bacterial consortia of S. uncinata FRs, isolated key bacterial strains, and evaluated their plant growth-promoting abilities through physiological experiments. Amplicon sequence variable (ASV)-based bacterial community analysis revealed that Sphingomonadales were most abundant in tissues forming FRs compared to healthy S. uncinata tissues. Microbial isolation yielded 28 strains belonging to the genera Sphingomonas, Rhizobium, and Tardiphaga, which were significantly enriched in FRs. Among them, Sphingomonas spp. and Rhizobium spp. exhibited strong activities in cellulose degradation, phosphate solubilization, and production of indole-3-acetic acid, a plant hormone. The effects of these strains on promoting increases in plant biomass and root development were verified through physiological experiments using Arabidopsis thaliana seedlings. In this study, ASV-based metabarcoding analysis and physiological assays with bacterial isolates demonstrated that the dominant bacteria in Antarctic FRs have the potential to promote plant growth in Antarctica. These findings contribute to the understanding of the dynamic development of the Antarctic terrestrial ecosystems, where plants, bacteria, and fungi interact closely under the influence of climate change.