Decoding the process of bacterial division

Duke University researchers have recently made great strides in understanding the mechanism of bacterial division. This success can bring new antibiotic treatments to prevent bacteria from multiplying.

Normally bacteria divide by forming a septum separating cells into two. This partition is called the 'Z ring' named after the FtsZ protein that forms a circular frame and then shrinks. In bacteria, the Z ring also contains dozens of other proteins. All have an important role in the process of division.

The Z ring usually forms in the cell membrane by combining with the FtsA protein that has one end attached to the inner membrane and the other end attached to the FtsZ protein. When the Z ring shrinks, it follows the membrane and separates the bacteria into two.

Cell biology research scientist Masaki Osawa conducted the separation of FtsA from this division system by creating FtsZ that can bind directly to the cell membrane. This protein is called 'FtsZ membrane' or FtsZ-mts.

The division of bacteria (Photo: microscopy-uk.org)

First, Osawa proved that the new protein, FtsZ-mts, has the same structure as the Z ring of bacteria. He then created a simplified cell division system in microscopic oil droplets called liposomes to describe the importance of FtsZ during the division process. He created the Z ring in this completely artificial system - the tiny liposome fat droplet that simulates the cell membrane in nature.

To do this, Osawa mixed liposomes with FtsZ and GTP - molecules that provide energy. On a microscope specimen, liposomes flow out and transform the shape in a test tube that mimics the shape of E. coli and other rod-shaped bacteria.

Research co-author Harold Erickson, a professor of cell biology, said: 'This is a happy coincidence when the size and shape of the liposome is similar to the stick-shaped bacteria. These tubular liposome droplets are microscopic structures, their formation is still mysterious. '

During the experiment, FtsZ-mts originally labeled fluorescent tubes were placed outside the liposome, but some tubular liposomes were attached to FtsZ inside. 'We do not understand how this happens, but this is the key point to discover , ' Osawa said.

Inside the liposome, FtsZ forms many closed belts in a line perpendicular to the length of the liposome like the formation of Z rings in bacteria. They also slide up and down, when they meet, they mount and form clearer belts. When the Z rings light up, they obviously pull the liposome into the inside.

'The Z-ring clearly forces the cells to shrink'. The team made a video of the contraction of the cell wall occurring at points with a bright Z ring. When GTP in the liposome is used up, tubular liposomes do not shrink anymore but return to their original shape.

According to Erickson, 'We believe that this simple system can replicate the mechanism that the earliest bacteria used to divide. At that time they may have only FtsZ. Osawa's experiment proved that FtsZ - the wire that attaches to the cell membrane - and the inner surface of the cell membrane is all necessary to create Z gold and create contraction force '.

Osawa stressed: 'Artificial Z rings are not strong enough to separate liposome droplets into two, perhaps because the liposome wall is much thicker than the bacterial cell membrane. We are continuing to create thinner liposomes to complete this division. '

Erickson said that the FtsZ in the bacterium is the ancestor of tubulin - the protein that makes microcapsules in animal cells and is the target of many anti-cancer drugs like taxol. Although FtsZ is not sensitive to taxol, anything that is learned from the nematode protein in bacteria helps us to understand microcapsules; thereby helping animal cells retain their shape and control their activities.