The MarBAG, based at Philipps-University Marburg and the Max-Planck-Institute for Terrestrial Microbiology in Marburg, Germany, employs X-ray crystallography to elucidate the fundamental mechanisms underlying the synthesis, assembly, and function of macromolecular machines and cellular structures. This research encompasses critical biological processes, including CO2 fixation pathways, flagellar biosynthesis, CRISPR-Cas systems, and phage-bacteria interactions. Additionally, our investigations extend to plant-pathogen interactions and the role of nucleotide-derived signaling molecules in cellular stress physiology and organization of bacteria and higher organisms. To enhance our structural characterization of macromolecular complexes that are challenging to crystallize, we have recently installed a 200 keV cryo-electron microscope at UMR. This advanced instrumentation enables routine screening and quality assessment of samples for cryoelectron microscopy.