A synthetic microbial community for soybean biofertilization designed via chlorophyll-based iterative selection.

Area of Science:

• Agricultural Microbiology
• Plant-Soil Interactions
• Synthetic Biology

Background:

• Soybean requires significant nitrogen for high protein content, relying on biological nitrogen fixation (BNF) via Bradyrhizobium symbiosis.
• Current single-strain Bradyrhizobium inoculants show inconsistent field performance due to interactions with native soil microbiota.
• Harnessing plant-soil-microbe interactions is key to improving soybean productivity and reducing synthetic fertilizer reliance.

Purpose of the Study:

• To develop and evaluate a synthetic microbial community (SynCom) for enhanced soybean inoculation.
• To engineer a SynCom using host-mediated microbiome engineering guided by plant traits.
• To assess the SynCom's effectiveness in improving nodulation and plant growth in non-sterile soil.

Main Methods:

• A SynCom comprising 9 Bradyrhizobium spp. and 14 soil isolates was created.
• Host-mediated selection using soybean leaf chlorophyll content guided eight rounds of community propagation.
• Community composition was analyzed using sequencing; SynCom performance was tested in non-sterile soil against controls.

Main Results:

• Recurrent selection significantly shifted community composition, favoring Bradyrhizobium diazoefficiens and enriching specific bacterial taxa.
• The engineered SynCom formed a cohesive, functionally enriched community with enhanced nitrogen transformation potential.
• The SynCom increased nodule number and soybean biomass compared to uninoculated controls and a commercial inoculant.

Conclusions:

• Plant-guided selection is effective in assembling beneficial rhizosphere communities.
• The developed SynCom represents a promising strategy for next-generation soybean bioinoculants.
• This approach can improve BNF, enhance soybean yield, and reduce reliance on chemical fertilizers.