Establishment and Effect of a Protist Consortium on the Maize Rhizosphere

Abstract

Protists are abundant in the rhizosphere, and protist inoculation onto plants has revealed protists’ roles in plant growth and development, disease suppression, and relationships with plant-beneficial bacteria. In this study, we evaluated the establishment of an 18-member defined protist consortium after inoculation onto germinated maize seedlings, along with the effects on the bacterial populations in the rhizosphere. Inoculated protists established a community that could be detected in the rhizosphere 3 weeks after inoculation. Plants inoculated with the protist consortium developed a bacterial community structure similar to that of plants inoculated with protist-free rhizosphere bacteria but different from that of uninoculated plants. This indicates that the protist cultures introduced rhizosphere-competent bacteria to the seedling. We also observed a plant growth phenotype, as inoculation with rhizosphere bacteria suppressed plant growth in the absence, but not the presence, of protists. Maize inoculated with an antibiotic-treated protist had lower biomass than plants inoculated with an untreated protist, indicating that growth promotion by protists depended on bacteria in the protist culture microbiome. This study shows that inoculation of germinated seeds establishes protist and bacterial communities on maize roots and that plant-detrimental effects of rhizosphere bacteria can be mitigated by the presence of protists.

Keywords

• bacteriology
• microbiome
• rhizosphere and phyllosphere
• soil ecology
• symbiosis