Tick-Bacteria Mutualism Depends on B Vitamin Synthesis Pathways

Area of Science:

• Microbial ecology
• Symbiotic relationships
• Eukaryotic evolution

Background:

• Microbial mutualisms are key to eukaryotic diversification and adaptation.
• Ticks, like Ornithodoros moubata, have specialized feeding habits.
• The bacterial genus Francisella includes pathogens and tick symbionts.

Purpose of the Study:

• To investigate the role of Francisella mutualisms in the blood-feeding lifestyle of ticks.
• To identify the specific function of Francisella F-Om in Ornithodoros moubata.

Main Methods:

• Physiological experiments to assess tick life history traits.
• Experimental elimination of Francisella F-Om.
• B vitamin supplementation as a restoration method.
• Genomic analysis of Francisella F-Om.

Main Results:

• Francisella F-Om was identified as an obligate nutritional mutualist for Ornithodoros moubata.
• F-Om synthesizes B vitamins deficient in the tick's blood meal.
• Elimination of F-Om caused developmental abnormalities, restored by B vitamin supplementation.
• F-Om is maternally transmitted to tick oocytes.

Conclusions:

• Francisella F-Om is essential for the life cycle of Ornithodoros moubata, providing vital B vitamins.
• This symbiosis demonstrates how microbial mutualisms facilitate adaptation to specialized diets.
• The genome of F-Om indicates a recent evolutionary shift from a pathogenic to a mutualistic lifestyle.