Date of Award
Spring 2020
Degree Type
Masters Thesis
Degree Name
Master of Science (MS)
School
Biological, Environmental, and Earth Sciences
Committee Chair
Dr. Dmitri V. Mavrodi
Committee Chair School
Biological, Environmental, and Earth Sciences
Committee Member 2
Dr. Janet Donaldson
Committee Member 2 School
Biological, Environmental, and Earth Sciences
Committee Member 3
Dr. Micheal Davis
Committee Member 3 School
Biological, Environmental, and Earth Sciences
Abstract
Pseudomonas synxantha 2-79 is a biocontrol agent that represents beneficial indigenous rhizobacteria that are broadly distributed in the Pacific Northwest, USA and flourish in the rhizosphere of commercially grown wheat under surprisingly arid conditions. The molecular adaptation of 2-79-like bacteria to plants growing in dry soils is poorly understood. We hypothesized that the ability of 2-79 to colonize and persist in the rhizosphere of water-stressed plants is underpinned by the formation of hydrating biofilms and the utilization of root exudates that contain plant-derived osmoprotectants called quaternary ammonium compounds (QACs). We tested this hypothesis by identifying waters stress response pathways in the 2-79 genome and then constructing a series of isogenic mutants deficient in one or more biofilm matrix and QAC transporters. The analysis of mutants revealed that under water-replete conditions, the QAC transporters function differentially and redundantly in the uptake of quaternary amines as nutrients. In contrast, under water stress, the QACs choline, betaine, and carnitine are accumulated preferentially for osmoprotection. Under drought stress, a mutant devoid of all known QACs transporters was less competitive in the colonization of the Brachypodium rhizosphere than its wild-type parental strain. The analysis of alg, psl, and eps biofilm matrix pathways revealed their role in the protection of 2-79 from desiccation. These pathways also contributed redundantly to the competitive colonization of plant roots. Our results confirm the importance of plant-derived QACs for microbial adaptation to the rhizosphere lifestyle and support the idea that the exchange of metabolites between plant roots and microorganisms profoundly affects and shapes the belowground plant microbiome under water stress.
Copyright
Clint Henry Pablo, 2020
Recommended Citation
Pablo, Clint Henry D., "Elucidating the Molecular Pathways Involved in the Fitness and Water Stress Response of Pseudomonas synxantha 2-79 in the Plant Rhizosphere" (2020). Master's Theses. 722.
https://aquila.usm.edu/masters_theses/722