Institute of Parasitology, Biology Centre of the Czech Academy of Sciences, České Budějovice, Czechia.
Vector Biology Section, Laboratory of Malaria and Vector Research, National Institute of Allergy and Infectious Diseases (NIAID), Bethesda, MD, United States.
Front Cell Infect Microbiol. 2024 Aug 13;14:1450353. doi: 10.3389/fcimb.2024.1450353. eCollection 2024.
Ticks are obligate hematophagous arthropods that transmit a wide range of pathogens to humans as well as wild and domestic animals. They also harbor a non-pathogenic microbiota, although our previous study has shown that the diverse bacterial microbiome in the midgut of is quantitatively poor and lacks a core. In artificial infections by capillary feeding of ticks with two model bacteria (Gram-positive and Gram-negative sp.), rapid clearance of these microbes from the midgut was observed, indicating the presence of active immune mechanisms in this organ. In the current study, RNA-seq analysis was performed on the midgut of females inoculated with either or sp. or with sterile water as a control. While no immune-related transcripts were upregulated by microbial inoculation compared to that of the sterile control, capillary feeding itself triggered dramatic transcriptional changes in the tick midgut. Manual curation of the transcriptome from the midgut of unfed females, complemented by the proteomic analysis, revealed the presence of several constitutively expressed putative antimicrobial peptides (AMPs) that are independent of microbial stimulation and are referred to here as 'guard' AMPs. These included two types of midgut-specific defensins, two different domesticated amidase effector 2 (Dae2), microplusin/ricinusin-related molecules, two lysozymes, and two gamma interferon-inducible lysosomal thiol reductases (GILTs). The antimicrobial activity assays of two synthetic mature defensins, defensin 1 and defensin 8, confirmed their specificity against Gram-positive bacteria showing exceptional potency to inhibit the growth of at nanomolar concentrations. The antimicrobial activity of midgut defensins is likely part of a multicomponent system responsible for the rapid clearance of bacteria in the tick midgut. Further studies are needed to evaluate the role of other identified 'guard' AMPs in controlling microorganisms entering the tick midgut.
蜱是专性吸血节肢动物，可将广泛的病原体传播给人类以及野生动物和家养动物。它们还携带非致病性微生物群，但我们之前的研究表明， 的中肠中多样化的细菌微生物组数量较少且缺乏核心。在通过毛细喂养给 tick 接种两种模式细菌（革兰氏阳性 和革兰氏阴性 sp.）的人工感染中，观察到这些微生物从中肠迅速清除，表明该器官存在活跃的免疫机制。在当前的研究中，对用 或 sp.或无菌水接种的 雌性的中肠进行了 RNA-seq 分析。与无菌对照相比，微生物接种并没有上调任何与免疫相关的转录本，但毛细喂养本身就触发了 tick 中肠的剧烈转录变化。对未进食的 雌性中肠的转录组进行手动注释，并结合蛋白质组分析，发现了几种组成型表达的推定抗菌肽（AMPs），这些肽与微生物刺激无关，这里称为“防御”AMPs。其中包括两种类型的中肠特异性防御素、两种不同的驯化酰胺酶效应物 2（Dae2）、microplusin/ricinusin 相关分子、两种溶菌酶和两种γ干扰素诱导的溶酶体硫醇还原酶（GILTs）。两种合成成熟防御素 1 和防御素 8 的 抗菌活性测定证实了它们对革兰氏阳性菌的特异性，在纳摩尔浓度下对 表现出异常的抑制生长作用。中肠防御素的抗菌活性可能是负责快速清除 tick 中肠细菌的多组分系统的一部分。需要进一步的研究来评估其他鉴定的“防御”AMPs 在控制进入 tick 中肠的微生物方面的作用。
