Symbiont-regulated serotonin biosynthesis modulates tick feeding activity

Area of Science:

• Microbiology
• Parasitology
• Molecular Biology

Background:

• Ticks are obligate blood-feeding arthropods crucial for nutrient acquisition and pathogen transmission.
• The molecular mechanisms regulating tick feeding behavior are not fully understood.
• Endosymbionts play vital roles in host physiology, but their impact on tick feeding is largely unknown.

Purpose of the Study:

• To investigate the role of the endosymbiont Coxiella (CHI) in regulating blood feeding in the tick Haemaphysalis longicornis.
• To elucidate the molecular pathways by which CHI influences tick feeding behavior.

Main Methods:

• Reduced abundance of Coxiella (CHI) in Haemaphysalis longicornis using tetracycline treatment.
• Restoration of feeding defects by providing CHI-derived precursors (chorismate, tryptophan) or 5-hydroxytryptamine (5-HT).
• Analysis of gene expression for aromatic amino acid decarboxylase (AAAD) and measurement of 5-HT levels.
• Inhibition of CHI chorismate biosynthesis using glyphosate.

Main Results:

• Reduced CHI abundance in ticks led to decreased blood intake.
• Supplementation with chorismate, tryptophan, or 5-HT restored the feeding defect.
• CHI-derived chorismate stimulates tick 5-HT biosynthesis by upregulating AAAD expression.
• Increased 5-HT levels in the synganglion and midgut promote tick feeding.
• Glyphosate inhibition of CHI chorismate biosynthesis suppressed blood-feeding behavior.

Conclusions:

• The endosymbiont Coxiella (CHI) is essential for regulating 5-HT biosynthesis in ticks.
• CHI influences tick feeding behavior through the modulation of 5-HT levels.
• This study reveals a novel mechanism linking microbial symbionts to host feeding physiology in ticks.