Bacterial symbionts of amoebae

Free-living amoebae are ubiquitous, they feed on other microbes and shape microbial communities. They also serve as transient hosts for facultative intracellular bacteria such as the human pathogen Legionella pneumophila and may carry bacterial symbionts in long-term stable symbiotic associations. Only few groups in the Alphaproteobacteria, the Betaproteobacteria, the Bacteroidetes, and the Chlamydiae occur as symbionts in amoebae, and closely related symbionts have been found in amoeba isolates from geographically distant sources, indicating a global distribution of these symbioses.

These obligate intracellular bacteria have evolved the ability to infect and establish symbiotic associations with amoebae independently and thus represent ideal model systems to investigate the diversity and evolution of the intracellular life style and underlying mechanisms for host-interaction.

We use a comprehensive, polyphasic approach including the complete array of omics technologies, biochemical characterization of key proteins, phylogenetic and evolutionary analysis to study amobae-associated symbionts. We have been focusing on chlamydial symbionts for over a decade, but we are also investigating the Bacteroidetes symbiont Amoebophilus asiaticus, the rickettsial symbiont Jidaibacter acanthamoeba, and the betaproteobacterial symbiont Procabacter.

Infection strategies used by extant bacterial pathogens have been developed during primordial interactions with unicellular eukaryotes, such as amoebae, as “evolutionary training ground”. The analysis of modern amoeba symbionts therefore also contributes to a better understanding of the evolution of pathogenicity and the emergence of bacterial pathogens.