Clear as mud redefined: Tunable transparent mineral scaffolds for visualizing microbial processes below ground.

Area of Science:

• Environmental microbiology
• Materials science
• Geomicrobiology

Background:

• Microbial processes in sediments are vital for biogeochemical cycles but difficult to study due to opaque matrices.
• Existing methods struggle to visualize microbial life within complex porous environments.

Purpose of the Study:

• To create optically transparent mineral scaffolds for visualizing microbial colonization and activity in sediment and rock microenvironments.
• To develop a tool for in situ and laboratory investigations of previously obscured microbial habitats.

Main Methods:

• Developed optically transparent cryolite mineral scaffolds using suspension-based, freeze-casting techniques.
• Controlled scaffold pore size and architecture by fine-tuning freezing parameters and solvents.
• Utilized epifluorescence microscopy and Raman spectroscopy for microbial visualization and activity measurements.

Main Results:

• Generated scaffolds mimic complex 3D sediment/rock structures with controllable porosity.
• Demonstrated compatibility with microscopy for visualizing microbial colonization up to 100 µm depth.
• Showcased potential for single-cell activity quantification using stable isotope probing coupled with Raman-FISH.

Conclusions:

• Cryolite scaffolds provide a novel method for studying microbial communities in opaque geological materials.
• This tool enables highly resolved, spatially explicit investigations of underground microbial distribution, activities, and interactions.
• The developed scaffolds are relevant for environmental field studies, as shown by visualization in seagrass rhizosphere sediments.