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Scientists Image Metabolites Secreted by Single Cells

Bacteria secrete small molecules for purposes that range from communication to self-defense. These processes are extremely challenging to study in situ because it is nearly impossible to link secreted molecules to specific populations of bacteria let alone individual cells in their natural environment. By combining mass spectrometry-based imaging with fluorescence in situ hybridization (FISH) scientists at the Max Planck Institute for Chemical Ecology are able to image secretion patterns of antibiotics and map them onto the FISH profile of the bacterial population that underlies it.

Both masspectrometric imaging (MSI) and FISH are well-established techniques. MSI uses a laser beam to excite ions in the material to be imaged. The resulting ions are analyzed and identified using a mass spectrometer while maintaining information about the spatial origin of the ions. The resulting image contains information about both the chemical composition of a material and its spatial organization. FISH allows visualization of species of interest in a population by using species-specific hybridization probes that can be visualized using fluorescence microscopy.

Using this approach Kaltenpoth et al mapped the secretion pattern of the antibiotics piericidin A1 and B1 secreted by Streptomyces pilanthi on the cocoon of its symbiont the beewolf wasp. The same cocoon was then analyzed by FISH. The resulting fluorescence microscopy images were overlayed with the MSI-generated map of antibiotic secretion allowing Kaltenpoth and colleagues to correlate antibiotic expression patterns with individual cells. This technique paves the way to better understanding microbial populations in the wild as well as their interactions with their environment.

Source: Max Planck Institute for Chemical Ecology

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