Friday, March 10, 2006

Discussion thread on Cell Division in Bacillus and Caulobacter.

Discussion thread on cell division in Bacillus subtilis and Caulobacter crescentus
This is designed to help with an assignment.

Put your questions and findings in the comments please.

Cell division is one of the most rapidly developing and exciting areas of bacteriology today .

How can a novice find out about it and do literature research on the topic for a short review of what is currently known?

The first professional step is to find a high quality recent scientific mini-review in the literature.

First go the NCBI-PubMed literature search engine here.

(If in doubt google NCBI and press the PubMed button.)

Type in something like this,

cell division Caulobacter review

and press enter (or return).

A literature search output will appear on the screen. Be aware there are various options for display and textdownloading. The full summary option is most useful. Buying a cheapish USB thumb-drive to help harvest this information will be a good investment too.

You get this high up on the output list

Trends in Cell Biology
Volume 15, Issue 7 , July 2005, Pages 343-345

doi:10.1016/j.tcb.2005.05.002 Research Focus

Bacterial DNA segregation by the actin-like MreB protein

Thomas Kruse and Kenn Gerdes E-mail The Corresponding Author

Department of Biochemistry and Molecular Biology, Campusvej 55, DK-5230 Odense M, University of Southern Denmark, Denmark

Available online 25 May 2005.

Faithful chromosome segregation is vital to all organisms. Eukaryotic cells use the tubulin-based cytoskeleton to segregate their chromosomes during mitosis. A handful of papers have provided convincing evidence that, in bacteria, this task is accomplished by the actin homolog MreB. In particular, a recent study by Gitai et al. demonstrates that MreB specifically binds to and segregates the replication origin of the bacterial chromosome.

Before we go on, note that the PubMed outut for this article has a Related papers hyperlink button. Pressing it will virtually complete your assignment research for you.

Now go to a good library and search for the full copy of the journal article. An electronic version is best, as you can cut and paste your own notes onto your brand new thumdrive just as I do here.

In the mini-review full text article you find all sorts of goodies about Bacillus Caulobacter and MreB

(Note MreB has been mentioned in the lectures.)

Microbe Pundit found this :

Could MreB form a bacterial mitotic-like machine?

It is now clear that bacteria contain true homologs of both tubulin (FtsZ) and actin (MreB and ParM). Could cytoskeletal elements contribute to DNA segregation in bacteria? Indeed, the DNA segregation machinery encoded by the E. coli plasmid R1 specifies a simple prokaryotic analog of the eukaryotic spindle apparatus. The plasmid-encoded ParM protein, an actin homolog, forms F-actin-like filaments that are responsible for the active movement of plasmid copies to opposite cell poles [Ref] 5 and 6. The chromosome of rod-shaped bacteria encodes another actin homolog called MreB. The structure of monomeric MreB is very similar to yeast actin (Figure 1), thus placing the evolutionary root of actin in the prokaryotic domain [7].


In addition to its role in cell shape determination, results from several research groups have linked MreB to a function in chromosome segregation. Expression of mutant forms of MreB with impaired ATPase activity in otherwise wild-type E. coli produced rod-shaped cells with unevenly distributed and abnormal MreB filament morphologies, leaving parts of the cells with no detectable MreB signal. Under these circumstances, severe chromosome segregation defects were observed [10]. Consistently, depletion of MreB in both B. subtilis and C. crescentus leads to a rapid defect in chromosome segregation, where replication origins fail to localize in a regular bipolar fashion 17 and 18. Together with the observation that MreB forms dynamic filaments that move away from the mid-cell towards opposite cell poles in B. subtilis, these result indicate that MreB could be part of a mitotic machinery involved in chromosome segregation 4 and 13.

Inhibitor confirms role for MreB in chromosome segregation

Recent convincing evidence for a direct role of MreB in chromosome segregation in Caulobacter crescentus was presented by the Shapiro laboratory [19]. They used a small molecule, S-(3,4-dichlorobenzyl)isothiourea (A22), that was originally identified in a screen for compounds that induce anucleate E. coli cells and a change in cell morphology from the normal rod-shape to a spherical form [20]. When administered to Caulobacter cells, A22 mimics the effects of MreB depletion and causes a rapid and reversible disintegration of the MreB cables.


9 L.J. Jones et al., Control of cell shape in bacteria: helical, actin-like filaments in Bacillus subtilis, Cell 104 (2001), pp. 913–922.

11 R.M. Figge et al., MreB, the cell shape-determining bacterial actin homologue, co-ordinates cell wall morphogenesis in Caulobacter crescentus, Mol. Microbiol. 51 (2004), pp. 1321–1332.

I have bolded portions of the text which are pure gold nuggets for an assignment.
If I had time I would mention them in a lecture.

Note how two major concepts developed the classroom, MreB "cables" and chromosome movement/partition are connected to one-another by this review. This field is surely moving fast.

Note also the quality of writing and the currentness of the information in the mini-review. It is a fine example of an assigment that I would award an 110% grade (or more).


Blogger Microbe Pundit said...

Dear Dr. Pundit

As i was studying lecture 4 the cell cycle, i got really confused with the
periseptal annulus and the Z-rings. The perseptal annulus determines the
location of the septum and the Z ring gives rise to the septum at the cell
division. What is the difference between these two or they are actually
the same thing?
Theresa L.

Dear Theresa

Thanks for such a good question.

Your question relates most directly to the Gram negative E. coli that has an IM and an OM and of course B. subtilis doesnt have an OM or an annulus.

(By the way, do you know if Caulobacter has an outer membrane (OM) ?. My memory says yes, but I could be wrong. Vibrio bacteria have a similar shape to Caulobacter and thats probably why I think they have an OM.

However a clear understanding of division in E. coli provides important concepts for understanding division in all other bacteria.

Understanding the terms you raise questions about depends on being clear about the two different membranes in Gram negative bacteria. OM and IM.
These correspond, pretty obviously, to Outer membrane and inner membrane=cytoplasmic membrane.

The periseptal anulus is only in Gram negative cells and is less important to understand than the Z-ring.

Lets start on the Z-ring:

It is thought to be present in all bacteria.
It is a ring forming inside the cell membrane (IM) starting just under the inner membrane and building inwards during division.

The annulus is ouside the cell membrane fusing the OUTER membrane OM with the cell membrane (IM).

It seems to form timewise before the Z-ring.

It seems to determine sites at which the Z-ring will eventually form.

M. Pundit Ph.D.

March 14, 2006 3:10 pm  
Blogger Microbe Pundit said...

Testing are you there Anonymous!

April 14, 2006 2:39 pm  

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