Extended: Developing synthetic microbial communities to improve sorghum performance.

Background: The rhizosphere represents a dynamic and complex interface between plant hosts and their microbial community. While it is recognized that manipulating the rhizosphere has the potential to improve plant performance, engineering the rhizosphere microbiome through inoculation has often proved challenging. This is in large part due to the competitive microbial ecosystem in which the introduced microbes must survive, and lack of adaptation to the specific metabolic and environmental pressures of the rhizosphere.

Objective: Paving the way for the use of rhizosphere microbiome as a tool is crucial to providing economic and sustainable solutions to current agricultural challenges. In our research, we aimed to create a defined synthetic rhizosphere community (SRC1) with the ultimate goals of evaluating 1) the degree to which growth conditions impact community composition of the community and 2) the impact of the community on host phenotype, Sorghum bicolor.

Methods: SRC1 was assembled from bacterial isolates that were either: 1) identified to play a potential role in community cohesion through network analysis, or 2) identified to benefit from host-specific exudate compounds. Growth of SRC1 was evaluated in vitro on solid media, in planta under gnotobiotic laboratory conditions and in the field.

Results: Our investigation revealed that SRC1 cohesion performs best when grown in the presence of the plant host in lab conditions, and that many lineages are lost from the community when grown either in vitro or in a native field setting. Importantly, we establish that SRC1 effectively promotes the growth of both above- and below-ground plant phenotypes in both laboratory and native field contexts. Furthermore, in laboratory conditions, these growth enhancements correlate with the transcriptional dampening of lignin biosynthesis in the host.

Conclusion: Our findings underscore the potential utility of synthetic microbial communities for modulating crop performance in both controlled and native environments.