Sulfolobus acidocaldarius, half a century of archaeal research.

Since its isolation from a Yellowstone hot spring in 1972, Sulfolobus acidocaldarius has become one of the most important model organisms for archaeal biology. Initially studied for its remarkable adaptation to high temperature and low pH, it has evolved into a genetically tractable system that has contributed substantially to our understanding of archaeal physiology, molecular biology, and evolution. Here, we summarize more than 5 decades of research on S. acidocaldarius, highlighting key developments in genetic and microscopy tools and their impact on our understanding of archaeal cell biology. Studies in this organism have improved our understanding of archaeal metabolism, chromosome organization, DNA replication and segregation, cell division, protein glycosylation, biofilm formation, and the assembly and regulation of archaeal surface structures, including archaella and type IV pili. Beyond fundamental biology, S. acidocaldarius has also served as a valuable source of thermostable enzymes and other biomolecules with biotechnological potential. Today, S. acidocaldarius is still one of the main model organisms for archaeal biology. Ongoing advances in genetics, imaging, and structural biology continue to expand its experimental potential, while its phylogenetic position within the Thermoproteota makes it a powerful system for investigating the evolutionary origins of eukaryotic cellular complexity.