Unconventional cell division in the Caribbean Sea

October 11, 2016, University of Vienna
Electron microscope image of the Robbea hypermnestra symbiont attached to its roundworm host. The proximal, host-attached pole is more invaginated that the free pole. Scale bar: 1 micrometer. Credit: Nikolaus Leisch, Nature Microbiology

Most bacteria divide by placing a protein called FtsZ at the division site. Traditionally, it was thought that FtsZ must organize into a ring in order to recruit a dozen of other proteins and together with them exert an homogeneous and simultaneous constricting force pinching the bacterium from side to side. Just as when one tries to squeeze a rod-shaped air-balloon with a thumb and a ring finger. Although it is still debated which one - among the division complex proteins - is generating the constricting force, it has never been debated that FtsZ forms a ring. Be it made by continuous FtsZ filaments or by short and partly overlapping ones, be it patchy, elliptic or toroid, a ring has been long believed to be sine qua non for cell division.

Bacterial cell biology textbooks have been written by studying microorganisms that can be grown in the laboratory. However, most microbes are not cultivable yet and can only be observed in their natural environment. This is the case of microbes engaging in intimate associations with multicellular organisms.

Silvia Bulgheresi and her team study the bacteria that grow and reproduce on the surface of a small family of marine nematodes, the Stilbonematinae. It is on those occurring around a tropical island in the middle of the Caribbean that the unconventional microbe was discovered. The analysis of this bacterium, the symbiont of the marine nematode Robbea hypermnestra reinvigorates the discussion about how the constrictive force that drives is generated.

The symbiont is a roughly 1 x 3 μm rod-shaped bacterium attached with one pole to the surface of its nematode host. First weird thing it does, is to orient its division plane parallel to its long axis, which makes it divide longitudinally instead of transversally (like conventional rod-shaped bacteria do). But as if building a wall and pinching a membrane over an approximately three times longer distance were not challenging enough, this resourceful organism tops it up by dividing asynchronously. Namely: it first invaginates at the nematode-attached pole and then at its free pole. "But the biggest surprise came as we searched for the FtsZ ring and we found none" explains Nikolaus Leisch, first author of the paper and currently a Postdoc at the Max Plank Institute, Bremen.

The division of the R. hypermnestra symbiont leaves the dazzled scientists at a loss to know which kind of evolutionary advantage this quirky division might bring. One possible explanation is that this would allow the symbiont to remain faithful to its worm host. "Longitudinal division might have evolved to transmit host attachment to both daughter cells. In other words, to avoid that one daughter cell is lost to the sand or the sea", speculates Bulgheresi.

The Smithsonian National Museum of Natural History field station Carrie Bow Cay in Belize. Credit: Olivier Carree
The division of the R. hypermnestra symbiont leaves the dazzled scientists at a loss to know which kind of evolutionary advantage this quirky division might bring. Scale bar: 5 micrometer. Credit: Nikolaus Leisch, Nature Microbiology

Explore further: Scientists deconstruct process of bacterial division

More information: Nikolaus Leisch et al. Asynchronous division by non-ring FtsZ in the gammaproteobacterial symbiont of Robbea hypermnestra, Nature Microbiology (2016). DOI: 10.1038/nmicrobiol.2016.182

Related Stories

Closing the ring

April 28, 2016

How bacterial cells divide in two is not fully understood. LMU physicists now show that, at high concentrations, a crucial protein can assemble into ring-shaped filaments that constrict the cell, giving rise to two daughter ...

Think big: Bacteria breach cell division size limit

September 15, 2014

The life of a cell is straightforward: it doubles, divides in the middle and originates two identical daughter cells. Therefore, it has been long assumed that cells of the same kind are similarly sized and big cells cannot ...

A Tiny Pinch from a 'Z-Ring' Helps Bacteria Cells Divide

October 11, 2007

In process that is shrouded in mystery, rod-shaped bacteria reproduce by splitting themselves in two. By applying advanced mathematics to laboratory data, a team led by Johns Hopkins researchers has solved a small but important ...

Researchers find pathway that controls cell size and division

July 30, 2007

Organisms precisely regulate cell size to ensure that daughter cells have sufficient cellular material to thrive or to create specific cell types: a tiny sperm versus a gargantuan egg for example. In single-celled organisms ...

Recommended for you

Semimetals are high conductors

March 18, 2019

Researchers in China and at UC Davis have measured high conductivity in very thin layers of niobium arsenide, a type of material called a Weyl semimetal. The material has about three times the conductivity of copper at room ...

0 comments

Please sign in to add a comment. Registration is free, and takes less than a minute. Read more

Click here to reset your password.
Sign in to get notified via email when new comments are made.