Keystone species

Ecosystem

Arabidopsis thaliana

Verrucomicrobia

Arabidopsis

Rhodococcus

Methylobacterium

16S ribosomal RNA

Bacteria

Biology

Gene

Mutant

Phyllosphere

Ecology

Sphingomonas

Actinobacteria

Microbacterium

Proteobacteria

Pseudomonas

Pantoea

Microbial ecology

Genetics

Multicellular organism

Nature Ecology & Evolution

Multicellular organisms, including plants, are colonized by microorganisms, some of which are beneficial to growth and health. The assembly rules for establishing plant microbiota are not well understood, and neither is the extent to which their members interact. We conducted drop-out and late introduction experiments by inoculating Arabidopsis thaliana with synthetic communities from a resource of 62 native bacterial strains to test how arrival order shapes community structure. As a read-out we tracked the relative abundance of all strains in the phyllosphere of individual plants. Our results showed that community assembly is historically contingent and subject to priority effects. Missing strains could, to various degrees, invade an already established microbiota, which was itself resistant and remained largely unaffected by latecomers. Additionally, our results indicate that individual strains of Proteobacteria (Sphingomonas, Rhizobium) and Actinobacteria (Microbacterium, Rhodococcus) have the greatest potential to affect community structure as keystone species. Conducting a series of removal experiments using synthetic leaf-inhabiting bacterial communities, the authors identify several keystone strains and show that priority effects drive phyllosphere community assembly.

Synthetic microbiota reveal priority effects and keystone strains in the Arabidopsis phyllosphere