Tick-Bacteria Mutualism Depends on B Vitamin Synthesis Pathways.
Mutualistic interactions with microbes have facilitated the radiation of major eukaryotic lineages [1, 2]. Microbes can notably provide biochemical abilities, allowing eukaryotes to adapt to novel habitats or to specialize on particular feeding niches [2-4]. To investigate the importance of mutualisms for the exclusive blood feeding habits of ticks, we focused on a bacterial genus of medical interest, Francisella, which is known to include both virulent intracellular pathogens of vertebrates [5, 6] and maternally inherited symbionts of ticks [7-9]. Through a series of physiological experiments, we identified a Francisella type, F-Om, as an obligate nutritional mutualist in the life cycle of the African soft tick Ornithodoros moubata. Francisella F-Om mutualism synthesizes B vitamins that are deficient in the blood meal of ticks. Indeed, experimental elimination of Francisella F-Om resulted in alteration of tick life history traits and physical abnormalities, deficiencies which were fully restored with an oral supplement of B vitamins. We also show that Francisella F-Om is maternally transmitted to all maturing tick oocytes, suggesting that this heritable symbiont is an essential adaptive element in the life cycle of O. moubata. The Francisella F-Om genome further revealed a recent origin from a Francisella pathogenic life style, as observed in other Francisella symbionts [6, 7, 10]. Though half of its protein-coding sequences are now pseudogenized or lost, Francisella F-Om has kept several B vitamin synthesis pathways intact, confirming the importance of these genes in evolution of its nutritional mutualism with ticks.
['Duron|Olivier|O|', 'Morel|Olivier|O|', 'Noël|Valérie|V|', 'Buysse|Marie|M|', 'Binetruy|Florian|F|', 'Lancelot|Renaud|R|', 'Loire|Etienne|E|', 'Ménard|Claudine|C|', 'Bouchez|Olivier|O|', 'Vavre|Fabrice|F|', 'Vial|Laurence|L|']
D000818:Animals D053898:Biosynthetic Pathways D005260:Female D005603:Francisella D008297:Male D026861:Ornithodoros D012281:Rickettsia D013559:Symbiosis D014803:Vitamin B Complex
B vitamins ticks Francisella hematophagy symbiosis