The immune factors involved in the rapid clearance of bacteria from the midgut of the tick Ixodes ricinus

• Published in: Frontiers in cellular and infection microbiology Vol. 14; p. 1450353
• Main Authors: Guizzo, Melina Garcia, Frantová, Helena, Lu, Stephen, Kozelková, Tereza, Číhalová, Kristýna, Dyčka, Filip, Hrbatová, Alena, Tonk-Rügen, Miray, Perner, Jan, Ribeiro, José M, Fogaça, Andrea C, Zurek, Ludek, Kopáček, Petr
• Format: Journal Article
• Language: English
• Published: Switzerland Frontiers Media S.A 13-08-2024
• Subjects: Animals; antimicrobial peptide; Antimicrobial Peptides - metabolism; Cellular and Infection Microbiology; defensin; Female; Gastrointestinal Tract - immunology; Gastrointestinal Tract - microbiology; Gene Expression Profiling; immune system; Ixodes; Ixodes - immunology; Ixodes - microbiology; Micrococcus luteus - immunology; midgut microbiome; Proteomics; tick; Transcriptome; Ixodes; defensin; immune system; tick; antimicrobial peptide; midgut microbiome; Micrococcus luteus
• ISSN: 2235-2988; 2235-2988
• DOI: 10.3389/fcimb.2024.1450353

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.