Rhizosphere-colonizing bacteria persist in the protist microbiome

Area of Science:

• Microbiology
• Plant Science
• Ecology

Background:

• Soil protists are diverse predators influencing rhizosphere bacteria.
• Protists host their own bacterial microbiomes.
• Previous work showed plants inoculated with protists had similar rhizosphere bacteria to the protist inoculum.

Purpose of the Study:

• To investigate how protist microbiomes affect the rhizosphere.
• To profile bacteria associated with eight diverse rhizosphere protist isolates.
• To compare protist culture microbiomes with maize rhizosphere communities post-inoculation.

Main Methods:

• Cultured eight diverse rhizosphere protist isolates for two years.
• Sequenced and profiled bacterial communities within protist cultures.
• Compared protist-associated bacteria with maize rhizosphere bacterial communities six weeks after protist inoculation.

Main Results:

• Protist inoculation enriched 13 bacterial amplicon sequence variants (ASVs) in the maize rhizosphere, comprising ~10% of the community.
• A median of 47% of the protist microbiome was highly abundant or enriched in the rhizosphere.
• Three of eight protist cultures positively impacted root biomass, but a mixture did not, indicating context-dependent effects.
• Protist-associated bacteria exhibited varied effects on protist growth in culture.

Conclusions:

• Rhizosphere protist cultures, even after long-term lab cultivation, host bacteria capable of colonizing maize rhizospheres.
• Diverse bacteria persist in protist cultures, suggesting protists may support their survival in soil ecosystems.
• These findings identify key rhizosphere-colonizing bacteria associated with protists, with potential applications in sustainable agriculture.