Spiroplasma eriocheiris FtsZ assembles the ring-like structure assisted by SepF

The FtsZ protein is involved in bacterial cell division. In cell-walled bacteria, such as Bacillus subtilis, FtsZ forms a ring-like structure, called the Z ring, at the cell division site and acts as a scaffold for cell wall synthesis. The inhibition of cell wall synthesis in B. subtilis has been shown to interfere with the function of the Z ring, causing a loss in cell division control. Spiroplasma, a cell wall-less bacterium, lacks most of the genes involved in cell division; however, the ftsZ gene remains conserved. The function of Spiroplasma eriocheiris FtsZ (SeFtsZ) remains to be determined. In the present study, we analyzed the biochemical characteristics of SeFtsZ. Purified SeFtsZ demonstrated lower polymerization capacity and GTPase activity than FtsZ from Escherichia coli and B. subtilis. We also investigated the relationship between SeFtsZ and SeSepF, which anchors FtsZ to the cell membrane, and found that SeSepF did not contribute to the stability of FtsZ filaments, unlike the B. subtilis SepF. SeFtsZ and SeSepF were produced in E. coli L-forms, where cell wall synthesis was inhibited. SeFtsZ formed ring-like structures in cell wall-less E. coli cells, suggesting that SeFtsZ forms Z rings and is involved in cell division independently of cell wall synthesis.