Defensins are the most diverse groups of antimicrobial peptides in invertebrate animals. In ticks, defensins show great potential as targets for tick control, and display future prospect for therapeutic drug development. In the present study, a novel defensin-like gene (Ds-defensin) contributing to the antimicrobial and antioxidant capacity of the tick Dermacentor silvarum was characterized. The full-length of the Ds-defensin gene was 382 bp, which displayed tissue-specific expression and was highly abundant in the salivary glands and carcasses of the adults. It encodes a 71-amino acid defensin-like protein, and the protein precursor is characterized by a 22-amino acid signal peptide and a 34-amino acid mature peptide. The peptide displayed potent activity against most of the tested gram-positive bacteria, including Staphylococcus aureus, S. carnosus and Nocardia asteroides, and one tested gram-negative bacterium, Psychrobacter faecalis. Scanning electron microscopy revealed that the cell wall and surface of treated bacteria became rough and gradually formed pores after a 30-min exposure to the Ds-defensin peptide. Additionally, the peptide also showed significant antioxidant capacity. The above results implied that the defensin-like peptide may play an important role in tick defense and the interaction with microorganisms.

防御素是无脊椎动物中抗菌肽种类最多的一组。在壁虱中，防御素显示出巨大的潜力，可作为壁虱控制的靶标，并显示出治疗药物开发的未来前景。在本研究中，表征了一个新的防御素样基因（Ds-defensin），它有助于壁虱Dermacentor silvarum的抗菌和抗氧化能力。Ds-防御素的全长该基因为382 bp，具有组织特异性表达，在成年唾液腺和and体中含量很高。它编码一个71个氨基酸的防御素样蛋白，该蛋白前体的特征是22个氨基酸的信号肽和34个氨基酸的成熟肽。该肽对大多数测试的革兰氏阳性细菌（包括金黄色葡萄球菌，鼠伤寒沙门氏菌和诺卡氏小球藻）以及一种测试的革兰氏阴性细菌屎肠杆菌都有较强的活性。。扫描电子显微镜显示，在暴露于Ds-防御素肽30分钟后，处理过的细菌的细胞壁和表面变得粗糙并逐渐形成孔。另外，该肽还显示出显着的抗氧化能力。以上结果暗示，防御素样肽可能在壁虱防御和与微生物的相互作用中起重要作用。