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 Ixodes ricinus is quantitatively poor and lacks a core. In artificial infections by capillary feeding of ticks with two model bacteria (Gram-positive Micrococcus luteus and Gram-negative Pantoea 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 I. ricinus females inoculated with either M. luteus or Pantoea 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 I. ricinus 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 in vitro 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 M. luteus 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.

• Klíčová slova
• Ixodes, Micrococcus luteus, antimicrobial peptide, defensin, immune system, midgut microbiome, tick,
• MeSH
• antimikrobiální peptidy metabolismus   MeSH
• gastrointestinální trakt mikrobiologie   imunologie   MeSH
• klíště * mikrobiologie   imunologie   MeSH
• Micrococcus luteus imunologie   MeSH
• proteomika MeSH
• stanovení celkové genové exprese MeSH
• transkriptom MeSH
• zvířata MeSH
• Check Tag
• ženské pohlaví MeSH
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• Názvy látek
• antimikrobiální peptidy MeSH

Ticks are ectoparasites that feed on blood and have an impressive ability to consume and process enormous amounts of host blood, allowing extremely long periods of starvation between blood meals. The central role in the parasitic lifestyle of ticks is played by the midgut. This organ efficiently stores and digests ingested blood and serves as the primary interface for the transmission of tick-borne pathogens. In this study, we used a label-free quantitative approach to perform a novel dynamic proteomic analysis of the midgut of Ixodesricinus nymphs, covering their development from unfed to pre-molt stages. We identified 1534 I. ricinus-specific proteins with a relatively low proportion of host proteins. This proteome dataset, which was carefully examined by manual scrutiny, allowed precise annotation of proteins important for blood meal processing and their dynamic changes during nymphal ontogeny. We focused on midgut molecules related to lipid hydrolysis, storage, and transport, opening a yet unexplored avenue for studying lipid metabolism in ticks. Further dynamic profiling of the tick's multi-enzyme digestive network, protease inhibitors, enzymes involved in redox homeostasis and detoxification, antimicrobial peptides, and proteins responsible for midgut colonization by Borrelia spirochetes promises to uncover new targets for targeting tick nymphs, the most critical life stage for transmission the pathogens that cause tick-borne diseases.

• Klíčová slova
• Borrelia, Ixodes, antimicrobial peptides, label-free quantification, lipid metabolism, midgut, protease inhibitors, proteases, proteome, ticks,
• MeSH
• klíště * parazitologie   MeSH
• proteom MeSH
• proteomika MeSH
• trávicí systém MeSH
• zvířata MeSH
• Check Tag
• zvířata MeSH
• Publikační typ
• časopisecké články MeSH
• práce podpořená grantem MeSH
• Názvy látek
• proteom MeSH