Evolution and Metabolic Potential of Francisella-like Endosymbionts of Ticks

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Repository URL:
10.15760/etd.3473; 10.15760/etd.5726
Gerhart, Jonathan Graham
Portland State University Library
Endosymbiosis; Ticks; Bacterial genetics; Genomics; Biology
report description
Endosymbiosis in arthropods involves intracellular bacteria that supply an array of benefits to the host. Endosymbionts likely enhance the health of ticks by provisioning amino acids such as cysteine and tyrosine, and cofactors such as biotin and folic acid that are not available in blood--the sole nutrient source of ticks. Endosymbionts of ticks are of special interest due to their close evolutionary relationship with tick-vectored pathogens that impact livestock and human health. For example, ticks typically contain Coxiella-like endosymbionts (CLEs) that are the closest relatives of the human pathogen Coxiella burnetii. In order to understand the evolutionary relationship between the mammalian pathogen Francisella tularensis, which is vectored by ticks, and the Francisella-like endosymbionts (FLEs) present in several ticks, we assembled the genomes of the FLEs in the hard tick Amblyomma maculatum and the soft tick Ornithodoros moubata using high-throughput sequencing. While this project was in progress, another group described the genome of an FLE in the soft tick Argus (Persicargas) arboreus. Utilizing the three genomes, we show that all FLEs evolved from a mammalian pathogen, a relationship that is converse to that of C. burnetii, which likely evolved from a tick-associated non-pathogenic ancestor. Additionally, our analyses indicate that FLEs are horizontally transferred between ticks, and due to their superior metabolic capabilities could replace ancestral endosymbionts with reduced genomes.