Defensin from the ornate sheep tick Dermacentor marginatus and its effect on Lyme borreliosis spirochetes

• Tick D. marginatus expresses defensin (defDM) in several organs after blood feeding.
• Mature defDM was purified from tick hemolymph and its full sequence was determined.
• Synthetic and well-folded defDM possesses anti-Gram-positive bacterial activities.
• DefDM reveals low hemolytic properties.
• Borrelia afzelii, the Lyme disease agent, was inhibited by synthetic defDM.

Expression of the previously reported defensin of the tick Dermacentor marginatus (defDM) was analysed in different organs by RT-PCR. mRNA of the defDM gene was detected in the hemolymph, midgut and salivary glands. Moreover defDM was isolated from the tick hemolymph using RP-HPLC and its sequence was determined by mass spectrometry and Edman degradation. Synthetic peptide was used for determining biological activities. The results showed an anti-Gram-positive bacterial role for the defensin. As D. marginatus ticks appear not to be vectors of the Lyme disease agent of the complex Borrelia burgdorferi sensu lato, we tested the influence of defDM on Borrelia afzelii. There is a very clear borrelicidal activity of the defensin, which is concentration dependent and suggests a possible role in the clearing of Borrelia ingested by D. marginatus ticks.