Ancient Truncated FtsZ Paralogs Likely Tune Cell Division in Hyphomicrobiales.

Bacterial cell division is a well conserved, tightly regulated process that allows the separation of two viable daughter cells. In most bacteria, the proteins that drive division, termed the divisome, are recruited to mid-cell by FtsZ after it polymerizes to form the Z-ring. Interestingly, FtsZ has undergone several independent duplication events across the bacterial kingdom. In this work, we searched for FtsZ GTPase protein sequences within alphaproteobacterial genomes and observed numerous ftsZ duplications in the order Hyphomicrobiales. Hidden Markov Modeling (HMM) supported the maintenance of two distinct lineages of FtsZ GTPase duplications among three families. The Nitrobacteraceae duplication, occurring in only the genus Bradyrhizobium, exhibits a different substitution pattern from that shared by the Phyllobacteraceae and Rhizobiaceae families. Within the Rhizobiaceae lineage, Agrobacterium tumefaciens contains three paralogs of FtsZ including the essential FtsZAT, and paralogs FtsZ1, and FtsZ3. We show that FtsZ1, but not FtsZ3, inhibits cell division when expressed continuously. A hyperactive allele of ftsW partially protected against continuous expression of ftsZ1, suggesting that FtsZ1 may function to negatively regulate septal peptidoglycan biosynthesis during cell division. Overall, these observations suggest that maintenance of FtsZ paralogs in some bacteria may help control the division process.