Decoding Root Biogeography: Building Reduced Complexity Functional Rhizosphere Microbial Consortia

Abstract The rhizosphere microbiome plays a crucial role in supporting plant productivity and contributes to ecosystem functioning by regulating nutrient cycling, soil integrity, and carbon storage. However, characterizing their functional attributes and microbial relationships remains challenging due to their complex taxonomic and functional compositions. To enable such studies, the development of reduced complexity microbial consortia derived from the rhizosphere microbiome of the natural ecosystem is highly desirable. Designing and assembling reduced complexity consortia that mimic natural communities with consistent, stable, predictable features are highly sought after but is challenging to deliver. Here we present our systematic controlled design towards successful assembly of several such rhizosphere derived reduced complexity consortia. From Brachypodium grown in natural soil under controlled lab conditions, we enriched the root-associated microbes, utilizing carbon compounds prevalent in Brachypodium root exudates. By transferring the enrichments every 3 or 7 days for 9 generations, we developed both fast and slow-growing microbial communities. 16S rRNA amplicon analysis revealed that both inoculum and carbon substrates significantly influence microbial community composition. For example, 1/10 R2A preferentially enriched Amplicon Sequence Variants (ASVs) from slow growing taxa vital to plant including Acidobacteria and Verrucomicrobia. Network analysis revealed that although fast and slow growing microbial consortia have distinct key taxa, the key hubs (keystone taxa) for both belong to genera with plant growth promoting (PGP) traits. This suggests that PGP bacteria might play a central role in controlling the microbial networks among rhizospheric microbiomes. Based on the stability and richness results from different transfers, most carbon substrates lead to microbial consortia with reduced complexity and high stability after a few transfers. The stability tests of the derived microbial consortia also showed high stability, reproducibility, and revivability of the constructed microbial consortia. Our study represents a significant step towards understanding and harnessing the potential of rhizosphere microbiomes, with implications for sustainable agriculture and environmental management.