Magnetotactic bacteria (MTB) are a phylogenetically heterogenous group of prokaryotes united by one special trait: their ability to sense magnetic fields. It is mediated by nano-sized iron mineral crystals, forming organelles known as magnetosomes. Allowing the bacteria to use earth"s magnetic field for orientation, magnetotaxis in particular facilitates MTB"s navigation through habitats characterized by a complex system of gradients. To this day, less than 30 species of these remarkable bacteria are validly published and a similar number has candidate status. However, it is possible to observe MTB in the sediment of the majority of water bodies, ranging from small rivers over lakes to the coastal areas of the oceans. Therefore, a tremendous amount of hidden biology awaits discovery in the realm of MTB.

To get a hold onto the diversity of MTB, we hosted a broad-range citizen science project in 2022 resulting in 225 sediment samples of Germany-wide origin. Using light microscopy, we screened each sampled habitat for MTB presence and collected information about their number and morphology. Next to many single-celled coccoid, rod-, oval- and spirilla-shaped MTB, we identified two spherical multicellular magnetotactic prokaryotes (MMP), one from a sampling site previously not known to host such an organism.

Combining micromanipulation with a single/oligo-cell approach, we investigated some of the most promising MTB in our samples in-depth. Isolated single/oligo cells were subjected to light microscopy, whole genome sequencing, and subsequent whole genome analysis. The results shed light on the selected MTB"s phylogenetic positions in the tree of life and the distribution/organization of their magnetosome gene clusters.

By increasing the number of available genomes, the metabolic capabilities of MTB could be identified to facilitate cultivation of novel species in the future while enabling the comparison of magnetosome genes from species of various habitats. Thereby, the project contributes to unveiling the diversity of magnetotactic bacteria and creates the base to broadscale research with these highly interesting specialists.