Method Development and Application of Mass Spectrometry Imaging to Study Symbiotic Relationships Between Bacteria and Host Organisms

Metabolic profiling can help shed light on cellular mechanisms; however a major technical challenge is to study endogenous metabolomic pathways without perturbing them. Most of the techniques currently in use for metabolomics studies in biological systems rely on tissue extracts which destroy the samples and result in the loss of information about analyte distribution within the tissue. Mass spectrometry imaging (MSI) has evolved as a promising technology to map a wide range of biomolecules in an anatomical context. In this dissertation, a multi-dimensional mass spectrometry-based platform was developed and applied to study interactions between bacteria and host organisms. Specifically, this work aimed to study the symbiotic relationship between soil bacteria and legume plants for agricultural and environmental sustainability applications, as well as the symbiosis between bacteria and leaf cutter ants and humans and our gut microbiota for the discovery of potentially novel antibiotics and antifungals. High-resolution, accurate-mass (HRAM) matrix-assisted laser desorption/ ionization (MALDI)-MSI was used to compare differentially treated biological samples, and liquid chromatography (LC)- electrospray ionization (ESI)- tandem mass spectrometry (MS/MS) coupled with database searching was used as a complementary mass spectrometry technique to identify interesting metabolites chosen from the MSI experiments. This work not only improves upon MSI by exploring novel sample preparation methods, but also presents a useful platform that integrates MALDI-MSI with ESI-MS in exploring the underlying chemistry of several biological symbiotic systems.