(22e) Screening the Rhizobiome for Plant Growth Promoting Bacteria That Improve Maize Growth and Development

Plant growth promoting bacteria (PGPB) are important for sustainable food production and have the potential to alleviate some of the environmental and health-related drawbacks of chemical fertilizers. However, many PGPB are limited in application because they are unreliable, inefficient, and have high host specificity, presenting considerable risks to farmers and producers. This is due in part to the poor survival of PGPB inoculants in plant rhizosphere. In this presentation, we report on the discovery and application of new, synergistic PGPB consortia that generate enhancements in corn growth metrics relative to single-strain inoculations by improving PGPB survival in the rhizosphere. Corn roots were sampled from a farmer's field in central Kansas and washed to remove the microbial communities from the rhizosphere. These microbial community members were then combined with Azospirillum brasilense, a well-known nitrogen fixing PGPB, in a novel, high-throughput microfluidic screening system. The device rapidly screened thousands of unique consortia consisting of A. brasilense combined with a small number of rhizosphere isolates to identify strain combinations that maximized A. brasilense growth and survival. Co-inoculation of A. brasilense onto corn seedlings with and without the synergistic isolate collections was then characterized in plant growth chambers and compared to single strain inoculations. Corn seedlings inoculated in consortia of A. brasilense and synergistic isolates showed higher growth rates, and in some cases, higher root and shoot mass and enhanced root architectures. Root colonization assays revealed that the synergistic consortia enabled A. brasilense to colonize at higher levels in the rhizosphere in order to enhance plant growth. These studies present a new approach for bioprospecting the rhizosphere of agriculturally-relevant crops to discover new and novel bacterial isolates for use in PGPB formulations, and suggests that combining well-characterized, nitrogen-fixing rhizobacteria with synergistic isolates in consortia has potential to improve the efficiency of PGPB biofertilizers.