Culturomics from field-grown crop plants using dilution to extinction, two-step library preparation and amplicon sequencing

Culturomics approaches have advanced microbial research by enabling the high-throughput isolation and characterization of a broader range of bacterial taxa, including some previously considered unculturable. Here, we present the testing and optimization of a protocol for isolating and identifying hundreds of cultivable microbes from field-grown plants. This protocol was tested and optimized using the root microbiomes of field-grown corn and pea plants under varying environmental conditions in ND, USA. By employing dilution-to-extinction culturing and a two-step barcoding PCR strategy targeting the V4 region of the 16S rRNA gene, we identified over 200 unique bacterial isolates. The optimized bioinformatic pipeline, built around the DADA2 package, ensured accurate amplicon sequence variant detection and taxonomy assignment. The resulting bacterial isolates span diverse phylogenetic groups, including plant-associated taxa known for promoting plant growth and mitigating stress. Our findings highlight the value of culturomics in generating microbial collections for synthetic community design and advancing plant-microbe interaction research. The protocol's scalability, cost-effectiveness and robust performance demonstrate its potential for widespread application in agricultural microbiome studies.