Aeromonas veronii and the leech Hirudo

Ex. Aeromonas veronii and Hirudo medicinalis

Characteristics of the symbiont/pathogen

Aeromonas veronii is a gram-negative, rod shaped bacteria (1) and has a genome size of about 4551783 base pairs (2). It can live in symbiotic realtionships (mutualistc, pathogenic) with a number of different vertebrates and it can also be free living (3).

Higher Order Taxa

Bacteria; Proteobacteria; Gammaproteobacteria; Aeromonadales; Aeromonadaceae; Aeromonas (2).

Aeromonas (11)[1]

Species

Aeromonas veronii

Characteristics of the host

A. veronii typically inhabits the digestive tract of, and shares in a symbiotic relationship with a number of differnt organisms of the genus Hirudo. Hirudo are a genus of leeches which are used for medicinal purposes and while there are many different species of Hirudo which A. veronii inhabit, this page will focus mainly on the relationship between A. veronii and H. medicinalis. A. veronii are most commonly found in the digestive tracts of the medicinal leech Hirudo medicinalis (3). This particular leech is widely used to prevent complications after surgery by alleviating potentially harmful blood clots (3). A. veroniican also be found residing in humans and other vertebrates, and may also inhabit fresh water environments (3).

H. medicinalis (12)[2]

Host-Symbiont Interaction

A. veronii and H. medicinalis share in a mutualistic relationship. It is thought that A. veronii and other Aeromonas species which live in the gut of H. medicinalis help the medicinal leech to break down and digest its blood meals (4). A. veronii is typically found as a pure culture existing in the gut of H. medicinalis and A. veronii can be transmitted vertically from one generation to the next (5). This transmission is thouhgt to occur when the eggs of the hermaphroditic H. medicinalis adult, hatch inside of their cocoon, which is full of fluids which are abundant with A. veronii, and the emerging offspring feed on the cocoon from which they came (5).

Molecular Insights into the Symbiosis

There have been many differnt studies done on the symbiotic partnership of A. veronii and H. medicinalis. Many of the studies have centered around how to better understand the specifics of the relationship between the two organsims and how their relationship may adversely affect the medicinal uses of the leech which A. veronii inhabits. This symbiotic partnership has also been exstensivley studied because H. medicinalis is a simple model organisms which scientists can use to better understand the nature of symbiotic relationships (6). Scientists have used comperative anlaysis and culture independent techniques to aid in these studies.

Ecological and Evolutionary Aspects

Like all symbiotic relationships, pathogens need to develop traits which allow them to bypass the biological defenses of the host, and successfully colonize and thrive inside of the host. It seems that in order for A. veronii to thrive inside of H. medicinalis they have developed lypoplysaccharides, outer membrane proteins, poylsacharide capsules, and a S layer (7). These are adaptations that A. veronii have aquired in an effort to bypass the biological defense mechanism of H. medicinalis called the complement-mediated killing response (7). Without these adaptations the relationship between A. veronii and H. medicinalis would not exitst.

Recent Discoveries

In recent years scientists have gained the ability to understand the communications which take place between symbionts and their hosts (8). This new found ability to understand and potentially manupulate the communications between host and symbiont may help scientitst overcome any complications which A. veronii may impose within a human host after being treated with H. medicinalis. It has also recently been shown that typical 16s rRNA sequencing does not effectively help scienists distinguish between differnt species of Hirudo (9). Though Hirudo have a relatively simple symbiotic interaction with thier symbionts, not all Hirudo species can be beneficial in medical uses and some well understood Hirudo species could be confused with less known species and this could lead to complications when Hirudo are applied for medicinal purposes. The proper identification of the different Aeromonas species which inhabit Hirudo could help to lessen potential complications, and the comparative analysis of certain house-keeping genes such as rpoD and gyrB could lead scientists to a more effective process of identification (10).

References

1 Mencacci, A, E. Cenci, R. Mazolla, Senia Farinelli, F. D’Alo, M. Vitali, and F. Bistoni. 2003. “Aeromonas veronii biovar veronii septicaemia and acute suppurative cholangitis in a patient with hepatitis B.” Journal of Medical Microbiology 52: 727-730.

2 http://www.genome.jp/kegg-bin/show_organism?org=avr

3 Laufer, A. S., M. E. Siddall, and J. Graf. 2008. “Characterization of the digestive-tract microbiota of Hirudo orientalis, a European medicinal leech. Antimicrobial Agents and Chemotherapy 74: 6151-6154

4 Indergand, S. and J. Graf. 2000. “Ingested blood contributes to the specificity of the symbiosis of Aeromonas veronii biovar sobria and Hirudo medicinalis, the medical leech.” Applied and Environmental Microbiology 66: 4735-4741.

5 Graf, Joerg. 2000. "Symbiosis of Aeromonas and Hirudo medicinalis, the medical leech." Ameirican Society of Microbiology. Presented at the 99th ASM General Meeting and the 6th International Aeromonas/Plesiomonas Symposium.

6 Grag, J., Y. Kikuchi, R. V. M. Rio. 2006. "Leeches and thier microbiota: naturally simple symbiosis models." Trends in Microbiology 14: 365-371.

7 Braschler, T. R., S. Merino, J. M. Tomas, and J. Graf. 2003. "Complement Resistance is essential, for colonization of the digestive tract of Hirudo medicinalis by Aeromonas strains." American Society of Microbiology 69: 4268-4271.

8 Ruby, E. G. 2008. "Symbiotic conversations are revealed under genetic interrogation." Nature Reviews Microbiology 6: 752-762.

9 Silver, A. C., D. Williams, J. Faucher, A. J. Horreman, J. P. Gagarten, and J. Graf. 2011. "Complex evolutionary history of the Aeromonas veronii group revealed by host interaction and DNA sequence Data." PLoS ONE 6: e16751.

10 Soler, L., M. A. Yanez, M. R. Chacon, M. G. Aguilera-Arreola, V. Catalan, M. J. Figueras, and A. J. Martinez-Murcia. 2004. "Phylogenetic analysis of the genus Aeromonas based on two housekeeping genes." International Journal of Systematic and Evolutionary Microbiology 54: 1511-1519.

11 http://www.food-bacteria.net/Bacteria/Aeromonas/

12 http://en.bestpicturesof.com/parasiten

Edited by [Gabrielle Woodford], students of Grace Lim-Fong

This template is just a general guideline of how to design your site. You are not restricted to this format, so feel free to make changes to the headings and subheadings and to add or remove sections as appropriate.