The evolution of symbiosis in the Bacteroidetes - Whole genome analysis of 'Candidatus Amoebophilus asiaticus'
 Free-living amoebae are abundant in terrestrial habitats and important predators of microorganisms. During evolution some bacteria have managed to evade phagocytosis by these protozoa and to use them as hosts, which ultimately led to stable and symbiotic associations. In total, five groups of  obligate intracellular Acanthamoeba symbionts, belonging to three different phyla, are known to date, but due to their only recent discovery and their intracellular life style our knowledge about these elusive bacteria is still scarce.
One of these amoeba symbionts, 'Candidatus Amoebophilus asiaticus' strain 5a2 belonging to the phylum Bacteroidetes, will now be sequenced in the framework of the DOE/JGI Community Sequencing Program. Members of the highly diverse phylum Bacteroidetes are ubiquitous and abundant in many habitats; they are considered to play an important role in biogeochemical cycles. The Bacteroidetes comprise only two major endosymbiont lineages: the first lineage contains the cockroach symbionts Blattabacterium spp. (Bandi et al., 1994) and the cicada symbiont 'Candidatus Sulcia muelleri' (Moran et al., 2005), the second lineage comprises the parasitoid wasp symbiont 'Candidatus Cardinium hertigii' (Zchori-Fein et al., 2004), and the amoeba symbiont 'Candidatus Amoebophilus asiaticus'(Horn et al., 2001).
Phylogenetic relationships of the candidate genus Amoebophilus with other members of the Bacteroidetes. 16S rRNA gene based maximum likelihood tree. [Click on image to enlarge] |
While the genomes of several intracellular Proteobacteria have been sequenced to date, the genome of 'Cand. Amoebophilus asiaticus' will be among the first symbiont genomes in the Bacteroidetes. Comparative genome sequence analysis of 'Cand. Amoebophilus asiaticus' will yield the first comprehensive insights into its biology. We will be able to determine molecular interaction mechanisms between the symbionts and their Acanthamoeba host cells, and to compare these to mechanisms found in other intracellular bacteria. From a phylogenetic perspective, the availability of the 'Cand. Amoebophilus asiaticus' genome sequence will allow us to investigate the evolution of the intracellular life style within the Bacteroidetes. Our analyses will be complemented by a collaboration with Dr. Martha S. Hunter (University of Arizona, Tucson, USA) who is sequencing the genome of the parasitoid wasp symbiont 'Candidatus Cardinium hertigii' (belonging to the sister clade of 'Cand. Amoebophilus asiaticus') in the DOE/JGI Community Sequencing Program.
Links
Bacterial endosymbionts of free-living amoebae
Project description on the JGI Homepage
Investigated by: Stephan Schmitz-Esser, Matthias Horn
This research is supported by:  
References
- Bandi, C., Damiani, G., Magrassi, L., Grigolo, A., Fani, R. and Sacchi, L. (1994). Flavobacteria as intracellular symbionts in cockroaches. Proc. R. Soc. Lond. B Biol. Sci. 257, 43-8.
- Horn, M. and Wagner, M. (2004). Bacterial endosymbionts of free-living amoebae. J. Eukaryot. Microbiol. 51, 509-14.
- Horn, M., Harzenetter, M.D., Linner, T., Schmid, E.N., Muller, K.D., Michel, R. and Wagner, M. (2001). Members of the Cytophaga-Flavobacterium-Bacteroides phylum as intracellular bacteria of acanthamoebae: proposal of 'Candidatus Amoebophilus asiaticus'. Environ. Microbiol. 3, 440-9.
- Moran, N.A., Tran, P. and Gerardo, N.M. (2005). Symbiosis and insect diversification: an ancient symbiont of sap-feeding insects from the bacterial phylum Bacteroidetes. Appl. Environ. Microbiol. 71, 8802-10.
- Zchori-Fein, E., Perlman, S.J., Kelly, S.E., Katzir, N. and Hunter, M.S. (2004). Characterization of a 'Bacteroidetes' symbiont in Encarsia wasps (Hymenoptera: Aphelinidae): proposal of 'Candidatus Cardinium hertigii'. Int. J. Syst. Evol. Microbiol. 54, 961-8.
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