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. We identified FtsZ GTPase protein sequences across alphaproteobacterial genomes, from representative genera for each family, 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. In A. tumefaciens, we show that FtsZ1, but not FtsZ3, inhibits cell division when overexpressed. A hyperactive allele of ftsW partially protected against overexpression of ftsZ1 suggesting that FtsZ1 may inhibit proper regulation of septal peptidoglycan biosynthesis during cell division. Overall, these observations suggest that maintenance of FtsZ paralogs in some bacteria which may fine tune the division process. Article SummaryGene duplication drives evolutionary innovation by providing raw genetic material and allowing microbes to acquire novel functions. Here, we explore the duplication of a gene encoding the essential cell division protein FtsZ in the Hyphomicrobiales and find that the duplication is primarily conserved in genera that interact with plant hosts. In A. tumefaciens FtsZ1 is not essential for cell division; however, overexpression of FtsZ1 inhibited cell division suggesting it may have a regulatory role during this essential process. This observation highlights the key role for gene duplication in the modulation of complex processes in bacteria.