Visualization of Lokiarchaeia and Heimdallarchaeia (Asgardarchaeota) by Fluorescence <i>In Situ</i> Hybridization and Catalyzed Reporter Deposition (CARD-FISH)
Michaela M. Salcher, Adrian‐Ștefan Andrei, Paul‐Adrian Bulzu, Zsolt Gyula Keresztes, Horia Leonard Banciu, Rohit Ghai
Abstract
Asgardarchaeota are considered to be the closest relatives to modern eukaryotes. These enigmatic microbes have been mainly studied using metagenome-assembled genomes (MAGs). Only very recently, a first member of Lokiarchaeia was isolated and characterized in detail; it featured a striking morphology with long, branching protrusions. In order to visualize additional members of the phylum Asgardarchaeota, we applied a fluorescence in situ hybridization technique and epifluorescence microscopy on coastal hypersaline sediment samples, using specifically designed probes for Heimdallarchaeia and Lokiarchaeia lineages. We provide the first visual evidence for Heimdallarchaeia that are characterized by a uniform cellular morphology typified by an apparently centralized DNA localization. Further, we provide new images of a lineage of Lokiarchaeia that is different from the cultured representative and with multiple morphologies, ranging from small ovoid cells to long filaments. This diversity in observed cell shapes is likely owing to the large phylogenetic diversity within Asgardarchaeota, the vast majority of which remain uncultured.