Mass Spectral Imaging to Map Plant–Microbe Interactions

Abstract

Plant–microbe interactions are of rising interest in plant sustainability, biomass production, plant biology, and systems biology. These interactions have been a challenge to detect until recent advancements in mass spectrometry imaging. Plants and microbes interact in four main regions within the plant, the rhizosphere, endosphere, phyllosphere, and spermosphere. This mini review covers the challenges within investigations of plant and microbe interactions. We highlight the importance of sample preparation and comparisons among time-of-flight secondary ion mass spectroscopy (ToF-SIMS), matrix-assisted laser desorption/ionization (MALDI), laser desorption ionization (LDI/LDPI), and desorption electrospray ionization (DESI) techniques used for the analysis of these interactions. Using mass spectral imaging (MSI) to study plants and microbes offers advantages in understanding microbe and host interactions at the molecular level with single-cell and community communication information. More research utilizing MSI has emerged in the past several years. We first introduce the principles of major MSI techniques that have been employed in the research of microorganisms. An overview of proper sample preparation methods is offered as a prerequisite for successful MSI analysis. Traditionally, dried or cryogenically prepared, frozen samples have been used; however, they do not provide a true representation of the bacterial biofilms compared to living cell analysis and chemical imaging. New developments such as microfluidic devices that can be used under a vacuum are highly desirable for the application of MSI techniques, such as ToF-SIMS, because they have a subcellular spatial resolution to map and image plant and microbe interactions, including the potential to elucidate metabolic pathways and cell-to-cell interactions. Promising results due to recent MSI advancements in the past five years are selected and highlighted. The latest developments utilizing machine learning are captured as an important outlook for maximal output using MSI to study microorganisms.

Secondary Ion Mass Spectral Imaging of Metals and Alloys

“…ToF-SIMS is commonly used to study biological samples, from microbes to drug analysis [4,140]. Biomedical surface preparation for implants, where residue can be harmful if not removed, has benefitted from SIMS's ability to characterize surface interfaces where interfacing of implant and bone is desired.…”

“…A major challenge associated with the application of SIMS is the complexity of datasets, especially for ToF-SIMS. It has big data challenges due to the nature of parallel data collection [4,161,162]. For ToF-SIMS analysis, multivariate analysis (MVA) is often used.…”

“…Secondary Ion Mass Spectrometry (SIMS) is a powerful mass spectral imaging (MSI) technique, and it has been extensively employed for comprehensive surface analysis and characterization of materials [1][2][3][4]. Its root traces back to 1910 [5], and its early applications are in inorganic materials and semiconductors.…”