The bacterial cell divides due to a force generated in a ring like structure (Fig.A) made of filaments of FtsZ protein. Such cellular fission occurs due to a contractile force which causes the ring (often called Z ring)to shrink . While shrinking, the Z ring also continuously exchanges filaments with the cellular medium, i.e., cytoplasm. Both, the origin of the contractile force as well as the process of filament exchange have been a puzzle for long.

Recently Prof. Anirban Sain of the Department of Physics and Shri Biplab Ghosh, a research scholar working under his guidance, have proposed a quantitative model which offers a plausible mechanism for this process of ring shrinkage (Fig.B). The model exploits the mechano-chemical properties of the FtsZ filaments, known from in vitro experiments. These include a) intrinsic curvature of the filaments, b) lateral attraction between them and c) GTPase property of the FtsZ protein, i.e., its ability to bind GTP and hydrolyze it to GDP. Hydrolysis of FtsZ-GTP to FtsZ-GDP leads to bending in the filaments. Interplay between lateral attraction among filaments, and hydrolysis induced bending, generates contractile stress in the Z ring and consequently leads to its radial contraction. The model has been validated through numerical simulation.

Figure Captions: A: Dividing bacteria with contracting Z ring B: The ring is modeled by a multilayered, filamentous structure consisting of FtsZ-GTP (open circles) and FtsZ-GDP (dark circles). Z ring continuously exchanges filaments with the medium (cytoplasm). Hydrolysis: FtsZ-GTP --> FtsZ-GDP leads to bending in the filaments. Interplay between lateral attraction among filaments, and hydrolysis induced bending, generates contractile stress in the Z ring and consequently leads to its radial contraction C: Shows time evolution of the Z ring through numerical simulation

Recently published in Physical Review Letters [101, 178101 (2008)] the work has also been highlighted by Nature-India (see URL below).

This finding is likely to open up avenues of further research and lead to significant applications. Deeper understanding of the mechanism of cell fission will enable biochemists to manipulate bacterial cell division in a controlled fashion and thus design new antibiotics. Presently, many of the available antibiotics function by rupturing the cell wall of the bacteria; but new drugs could target the Z ring. Using drugs that prevent Z ring formation or contraction may emerge as a viable alternative for blocking bacterial cell division. Such alternatives will be necessary in the future, given the alarming rise in antibiotic resistance in bacteria.

For more details:

• http://www.nature.com/nindia/2008/081111/full/nindia.2008.317.html

• http://www.phy.iitb.ac.in/doku/doku.php/faculty/asain/home

Acknowledgement: The authors of this work wish to thank Prof. Dulal Panda of the School of Biosciences and Bioengineering, IIT Bombay, for enthusing them to work on this biological phenomenon.