FtsZ forms biomolecular condensates in a polar-growing Alphaproteobacterium

Area of Science:

• Bacterial cell division
• Protein biochemistry
• Microbiology

Background:

• FtsZ is a conserved tubulin homolog essential for bacterial cell division.
• Alphaproteobacterial FtsZ proteins possess longer intrinsically disordered regions than E. coli FtsZ, suggesting altered assembly properties.
• Previous studies confirmed FtsZ condensates in vitro under crowding conditions but lacked in vivo evidence.

Purpose of the Study:

• To investigate the in vitro and in vivo condensate-forming properties of Alphaproteobacterial FtsZ.
• To compare the behavior of Agrobacterium tumefaciens FtsZ (FtsZ_At) with Escherichia coli FtsZ (FtsZ_Ec).
• To explore the potential role of FtsZ condensates in Alphaproteobacterial cell cycle regulation.

Main Methods:

• Purification and in vitro characterization of FtsZ_At under molecular crowding conditions.
• Induction of filament formation from FtsZ_At condensates using GTP.
• In vivo imaging of FtsZ_At and another Alphaproteobacterial FtsZ in Agrobacterium tumefaciens and Caulobacter crescentus.
• Fluorescence recovery after photobleaching (FRAP) to assess dynamic assembly and coalescence of FtsZ condensates.

Main Results:

• Purified FtsZ_At readily formed dynamic condensates in vitro.
• GTP addition induced filament formation radiating from FtsZ_At condensates.
• FtsZ_At formed similar dynamic foci and filaments in vivo, confirmed by FRAP.
• Alphaproteobacterial FtsZs exhibit a strong tendency to form condensates in vitro and in vivo, contrasting with FtsZ_Ec.

Conclusions:

• FtsZ_At forms polar condensates in Agrobacterium tumefaciens cells during normal growth.
• These condensates may sequester FtsZ_At before cell division, potentially as an adaptation to slow generation times.
• Condensate formation by Alphaproteobacterial FtsZs likely represents a conserved mechanism for cell cycle control in this bacterial class.