Non FtsZ based division in Thaumarchaea

The nature of the evolutionary relationship between bacteria, eukaryotes and archaea is not clear. An interesting feature of the PVC is that some members, like some archaea, lack the otherwise ubiquitous FtsZ division protein. The lack of the otherwise ubiquitous FtsZ opens the question of how is cell division achieved in those organisms. Pelve et al. Mol. Microbiol (2011) demonstrate that in the thaumarchaea N. maritimus, an organism with one of the smallest genomes amongst free living organisms, it is the Cdv proteins, and not FtsZ, that localize to division sites. The authors found that the FtsZ protein did not temporally neither spatially correlate with nucleoid segregation and no band or ring structures were observed. Instead, FtsZ was distributed in the cell in a mainly uniform intracellular distribution, regardless of cell cycle stage, as determined by cell size or DNA distribution. Thus, not only did the authors established that N. maritiums utilizes the Cdv machinery for cell division, they also demonstrated that it did not use FtsZ for this, a unique feature in FtsZ function. Thus division in Thaumarchaea is based on Cdv proteins and not on FtsZ machinery, and is likely to be similar to crenarchaea, an archaea with Cdv and not FtsZ encoded in its genome. What function FtsZ fulfills in thaumarchaea remains an open question. Since they couldn't detect a cytokinesis function for FtsZ, the authors propose that the protein has evolved a different function in thaumarchaea. In line with this proposal, thaumarchaeal FtsZ sequences are phylogenetically separated from bacterial and euryarchaeal FtsZ groups. The observed pattern could be a transition point from a FtsZ-based division mechanism to a non FtsZ-based one. The pattern of FtsZ and Cdv machinery homologues in other prokaryotes indicates that further division variants should be found out there. It seems to me that it would be important to characterize them to get a full coverage of cell division mechanisms.