Prosthecobacter spp.: A story of holdfasts and mustaches

This week I want to highlight Prosthecobacter fusiformis and related species from the genus Prosthecobacter. P. fusiformis is an interesting organism; however I must admit that I discovered it randomly by picking a taxon found in every sample (eight sites total) in one of my datasets. Yes I realize that many may regard this as an odd way to pick a bacterium to write about, but I feel that this was an appropriate way to discover an organism which I knew very little about.

Let’s again start with a little taxonomy (for those into that type of thing):

Phylum – Verrucomicrobia
Class- Verrucomicrobiae
Order – Verrucomicrobiales
Family – Verrucomicrobaiceae
Genus – Prosthecobacter

The Prosthecobacter genus has very few cultured representatives, but it is one of the more interesting groupings I have come across recently. This genus helped to distinguish Verrucromicrobia as a valid phylum of Bacteria. Before the characterization of this group there was little evidence to separate Verrocomicrobia from the other phyla due to the lack of cultured representatives. The inclusion of this second genus (along with molecular evidence of course) which included cultured organisms (even though not many) provided better evidence for the distinction of the phylum. Furthermore, with the use of molecular tools we now know that this phylum is distinct and we have evidence of other (non cultured) organisms that group with Verrucomicrobia. Secondly, all of the cultured representitives of Prosthecobacter are morphologically distinct. This is a rare phenomenon in any group of bacteria. Four species of Prosthecobacters have been carefully characterized and all have distinct standard length and widths as well as curviness and the presence or absence of vibrioid morphology (you may need to look this up for yourself: one of my favorites though) (Figure 1, from Hedlund et al., 1997). Furthermore, in my opinion, P. dejongei should be called the mustache bacteria. Seriously, you can’t look at panel D below and not think of a French mustache. Awesome!!!! I find that this morphology is quite interesting, but I wonder why. Why is there a mustache bacteria? Why are some sister taxa just slightly longer than others? Why are some narrow and straight while others have adapted the vibrioid morphology

So where does this organism get its name? Prosthecobacter refers to the terminal prosthecae found on all of the cells. Prosthecae are a cellular appendage which includes a holdfast that is used to attach to surfaces. Due to the presence of the prosthecae these organisms were originally placed with the Caulobacter (alpha proteobacteria) which are the best known group of prosthecate bacteria. However, it was later discovered that Prosthecobacter do not divide asymmetrically to produce motile (with no prosthecae) and non-motile (with prosthecae) cells. Instead they divide laterally, and thus all daughter cells have prosthecae and remain non-motile. Due to this type of division, Prosthecobacter produce clumps of cells that radiate out along the attached surface. I’m sure that if we were able to image, without disruption, surfaces containing this organism we would be able to find intricate patterns on surfaces. I wonder what the patterns of mustache bacteria would look like?

Ok, so maybe I didn’t only highlight P. fusiformis. Obviously I am more interested in P. dojongei but you still get the point. The genus Prosthecobacter is a great example of the extreme diversity and beauty of aquatic microbes and microbes in general. I still only knew little about this group of organisms, but I find them highly fascinating and I hope you now do as well. Questions, Comments: All welcome!!!!!

Brian P. Hedlund, John J. Gosink & James T. Staley. 1997. Verrucomicrobia div. nov., a new division of the Bacteria containing three
new species of Prosthecobacter. Antonie van Leeuwenhoek 72: 29–38.

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