AVS 66th International Symposium & Exhibition
    Biomaterial Interfaces Division Wednesday Sessions
       Session BI+AS-WeM

Paper BI+AS-WeM11
Chemical Imaging of Root-Microbe Interactions

Wednesday, October 23, 2019, 11:20 am, Room A120-121

Session: Microbes and Fouling at Surfaces
Presenter: Vaithiyalingam Shutthanandan, Pacific Northwest National Laboratory
Authors: V. Shutthanandan, Pacific Northwest National Laboratory
A. Martinez, Pacific Northwest National Laboratory
R. Boiteau, Pacific Northwest National Laboratory
Correspondent: Click to Email
Nutrient mobilization from soil minerals is critical for plant growth, particularly in marginal lands with high pH soils or low phosphate and iron availability. Rhizospheric bacteria enhance plant growth by converting root exudates such as sugars and amino acids into organic acids and chelating molecules that enhance mineral dissolution and improve the availability of nutrients such as phosphorous and iron. Hence, understanding the effect of iron availability on metabolite exchange between plant and micro-organism is crucial. The spatial proximity of bacteria to root tissue of specific composition and sites of root secretion is one key aspect of this exchange. In this work, the model grass Brachypodium and the bacteria Pseudomonas fluorescens are used as a model system for studying rhizosphere interactions that improve metal bioavailability. Brachypodium was grown under four different conditions such as: (1) + Fe, (2) – Fe, (3) + Pseudomonas + Fe, (4) + Pseudomonas – Fe. The plants were grown for 2 weeks in the hydroponic solution and removed from the system and the root samples were analyzed using Helium Ion Microscope (HIM) for spatial organization of bacteria within the rhizosphere of Brachypodium and X-ray photoelectron spectroscopy (XPS) for chemical imaging. HIM results clearly show bacteria colonies on the root surfaces. However, these colonies were populated preferentially within grooved structures along the surface of the root. We hypothesize that there are compositional differences in the surface of the root area that explain the presence of these ‘hotspots’. Roots exposed with iron show larger bacteria colonies than the roots without iron content. XPS imaging measurements on these samples revealed four predominant compositional classes, lipids/lignin, protein, cellulose and uronic acid that were spatially resolved across the surface of the main root with ~10 m resolution. Carbon and oxygen concentrations were almost constant among these samples and also constant along the individual roots. On the other hand, there is a clear variation in the concentrations of nitrogen and potassium along the root as well as among the samples. Discussion on the results and their implications will be discussed in this presentation.