Why Sequence Bacteroidetes?

Candidatus Amoebophilus in an amoeba host cell, visualized by fluorescence in-situ hybridization with symbiont-specific probes.

Symbiosis is a tremendously creative force in evolution. Prokaryotes in particular are critical partners with eukaryotes: humans rely on symbiotic bacteria in their gut and on their skin; plants depend on symbiotic bacteria and fungi, and many if not most arthropods carry intracellular bacterial symbionts, just to name a few examples. The processes and interactions underlying and shaping symbiotic associations are, however, still poorly known. The highly diverse bacterial phylum Bacteroidetes contains only two major endosymbiont lineages described to date, one of them being represented by the sister taxa ‘Candidatus Amoebophilus asiaticus’, a symbiont of free-living amoebas, and ‘Candidatus Cardinium hertigii’, a symbiont of arthropods. Both symbionts are obligately intracellular and cannot be cultivated in cell-free media. While many intracellular symbiont genomes have been sequenced in the Proteobacteria, the genomes of these two organisms will be among the first symbiont genomes in the Bacteroidetes. Comparative genome sequence analysis will yield the first comprehensive insights into their biology.

Sequencing will make it possible to determine molecular interaction mechanisms between the symbionts and their respective host cells, and to compare these to mechanisms found in other intracellular bacteria. Comparative genome analysis of C. Amoebophilus asiaticus and the chlamydia-related amoeba symbiont Protochlamydia amoebophila will help to elucidate how largely unrelated bacteria belonging to different phyla have adapted to intracellular life in the same eukaryotic host (Acanthamoeba). Comparative genomics of C. Cardinium hertigii with Wolbachia will shed new light on the genes necessary for reproductive host manipulation. From a phylogenetic perspective, the availability of the C. Amoebophilus asiaticus and the C. Cardinium hertigii genome sequences will make it possible to investigate the evolution of the intracellular lifestyle within the Bacteroidetes and the adaptation to different eukaryotic hosts. Researchers will also be able to analyze the process of genome reduction in this phylum--a key process during evolution of intracellular bacteria, currently almost exclusively studied using Proteobacteria as examples.

Principal Investigators: Matthias Horn (Univ. of Vienna) and Martha S. Hunter (Univ. of Arizona)