Abstract
Our understanding of the metabolites involved in the interactions between small symbiotic animals and bacteria or other eukaryotes that reside within their body is extremely limited. This gap in knowledge originates from a methodological challenge, namely to connect metabolites to the histological changes in host tissues throughout colonization and persistence of beneficial and parasitic (micro)organisms in situ.
To close this gap, we developed chemo-histo-tomography (CHEMHIST), a culture-independent approach to connect anatomic structure and metabolic function in millimeter-sized symbiotic animals. CHEMHIST combines spatial metabolomics based on mass spectrometry imaging (MSI) and microanatomy-based micro-computed X-ray tomography (microCT) on the same animal. Both high-resolution MSI and microCT allowed us to correlate the distribution of metabolites to the same animal’s three-dimensional (3D) histology down to sub-micrometer resolutions. Building CHEMHIST upon in situ imaging approaches, we sampled an earthworm from its natural habitat and created an interactive 3D model of its physical and chemical interactions with bacteria and parasitic nematodes in its tissues. Our CHEMHIST protocol is compatible with other molecular techniques, which include tissue specific DNA sequencing and localization of bacteria using fluorescence in situ hybridization (FISH) to complement the spatial metabolomics data.
We demonstrate on an earthworm, a key species for soil ecosystem-functioning across the globe that combining MSI and microCT offers a powerful platform to connect metabolic and anatomic phenotypes of small symbiotic animals in situ.
Significance Metabolites mediate the establishment and persistence of most inter-kingdom symbioses. However, the cellular- and organ-scale distributions of the metabolites involved in the symbiotic interactions in animals remain poorly understood. This gap originates from a missing link between anatomic structure and metabolic function at different life stages of symbiotic animals, such as the developmental and colonization status of the host. We addressed this problem by developing a culture-independent imaging approach termed chemo-histo-tomography (CHEMHIST), which combines micro-computed X-ray tomography and mass spectrometry imaging as key technologies. With CHEMHIST we created a 3D snapshot of an earthworm, connecting its anatomic phenotype and spatial chemistry, which revealed its metabolic interactions with symbiotic bacteria and parasitic nematodes in situ.
Competing Interest Statement
The authors have declared no competing interest.