Date of Award

Fall 12-2018

Degree Type

Masters Thesis

Degree Name

Master of Science (MS)


Biological, Environmental, and Earth Sciences

Committee Chair

Dmitri Mavrodi

Committee Chair School

Biological, Environmental, and Earth Sciences

Committee Member 2

Kevin Kuehn

Committee Member 2 School

Biological, Environmental, and Earth Sciences

Committee Member 3

Micheal Davis

Committee Member 3 School



In contrast to well-studied mechanisms of drought tolerance in plants, the interactions between plants and their microbiome during water stress are still poorly understood. This missing knowledge is crucial for the exploitation of beneficial microbial communities to improve the sustainability of agriculture under changing climatic conditions. The research described here bridged this gap by focusing on the molecular interactions between beneficial rhizobacterium Pseudomonas synxantha 2-79 and annual grass Brachypodium distachyon Bd21. 2-79 exemplifies a group of rhizobacteria associated with dryland wheat, while B. distachyon originates from the Middle East and has emerged as a model for valuable biomass, food, forage, and turf crops. The experimental system was used to test the hypothesis that the adaptation of rhizobacteria to water stress is mediated by the exchange of metabolites between the host plant and its microbiota. Results revealed that Brachypodium root exudates contain a mixture of plant metabolites that serve as carbon and energy sources for rhizobacteria and include compounds that act as osmoprotectants and may help rhizobacteria maintain physiological activity and mutualistic interactions with their plant host in dry soils. The genome of P. synxantha 2-79 encodes numerous pathways involved in de novo synthesis and uptake of osmoprotectants and formation of biofilms for protection from desiccation. Some of these pathways are conserved across many taxa, while others are strain-specific and may contribute to the differential affinity toward plants growing in under different soil water regimens. Future studies will inactivate these pathways and test resultant mutants for rhizosphere fitness under drought stress.