Date of Award:

8-2019

Document Type:

Thesis

Degree Name:

Master of Science (MS)

Department:

Biological and Irrigation Engineering

Advisor/Chair:

David W. Britt

Co-Advisor/Chair:

Elizabeth Vargis

Third Advisor:

Astrid Jacobson

Abstract

The area around a plant’s roots hosts a complex and diverse microbial community. This environment can include a large number of bacteria that live on the surface of the root and benefit from the nutrients that the roots exude into the soil. These microbes can in turn be beneficial to the plant by protecting the roots from harmful fungi or stressful environmental conditions such as drought. In this thesis, several root-mimetic systems (RMSs) were developed for the study and growth of plant-beneficial bacteria in the laboratory environment. The RMS uses a porous hollow fiber used in hemodialysis as a surface for microbial growth. This fiber can either be draped into liquid nutrients or nutrients can be pumped through the hollow fiber with seepage through pores in the fiber to the outside. These systems are simple but well-controlled models of how a root would feed a bacterial community. The RMSs can be used to study how bacteria receiving nutrients through the RMS react to external factors, and if the bacterial response varies with nutrients received through the fiber. One such application is to study how plant colonizing microbes react to stressors like nanoparticle technology, a growing part of the fertilizer industry.

Several different commercial hollow fiber membranes were explored as possible surfaces for microbe attachment. A synthetic polysulfone / polyvinylpyrrolidone hollow fiber membrane, treated with bleach to change the surface properties, was found to be a favorable surface for attachment of the beneficial root-colonizing microbe Pseudomonas chlororaphis O6 (PcO6). In addition to hollow fiber membrane chemistry, the nutrient composition delivered to the bacteria strongly influenced surface colonization and biofilm formation. Thus, using the hollow fiber root model, bacteria can be studied with respect to their responses to changes in nutrient composition as well as their response to stressors such as nanoparticles. Contrasted with studying bacteria on a living root, the model systems developed in this thesis allow microbes to be investigated without the added complexity of unknown variations in the nutrients that the roots pump into the soil.

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