Cell division is fundamental characteristic for all living organisms, and forms the basis of evolution to three domains of life on Earth: Bacteria, Eukarya, and Archaea. Compared to Bacteria and Eukarya, little is known about cell division mechanism in Archaea, despite its importance to understanding the origin and evolution of life.
Cell division in bacteria is driven by one FtsZ, a tubulin-like protein that forms a mid-cell contractile ring, whereas many archaea are now known to carry two FtsZ homologues from two distinct families. We studied the function of the two FtsZ genes in the model archaeal organism Haloferax volcanii [1]. By combining genetic targeting techniques and various advanced microscopy approaches, we found that two FtsZ genes are not essential for cell viability but essential for proper cell division, and they have different roles. These two FtsZ proteins co-localise as a ring around mid-cell that constricted during cytokinesis. However, FtsZ1 can assemble rings independently of FtsZ2 and also stabilises FtsZ2 in the ring, whereas FtsZ2 ring formation generally required FtsZ1 and is primarily involved in constriction mechanism. Different from cell division in most bacteria that involve the inward synthesis of peptidoglycan guided by FtsZ treadmilling, here we show that in archaea with a single S-layer wall FtsZ1 primarily acts as a regulator or scaffold to affect cell division and shape, and FtsZ2 promotes constriction of an S-layer envelope, where an internal constriction force might dominate the division mechanism. This study provides a new level of understanding about cytokinesis mechanisms in the Archaea domain, and advances our knowledge of the evolution of cell division machinery and how life evolved on Earth.