Anti-Tick Microbiota Vaccine Impacts Ixodes ricinus Performance during Feeding

Abstract

The tick microbiota is a highly complex ensemble of interacting microorganisms. Keystone taxa, with a central role in the microbial networks, support the stability and fitness of the microbial communities. The keystoneness of taxa in the tick microbiota can be inferred from microbial co-occurrence networks. Microbes with high centrality indexes are highly connected with other taxa of the microbiota and are expected to provide important resources to the microbial community and/or the tick. We reasoned that disturbance of vector microbiota by removal of ubiquitous and abundant keystone bacteria may disrupt the tick-microbiota homeostasis causing harm to the tick host. These observations and reasoning prompted us to test the hypothesis that antibodies targeting keystone bacteria may harm the ticks during feeding on immunized hosts. To this aim, in silico analyses were conducted to identify keystone bacteria in the microbiota of Ixodes nymphs. The family Enterobacteriaceae was among the top keystone taxa identified in Ixodes microbiota. Immunization of α-1,3-galactosyltransferase-deficient-C57BL/6 (α1,3GT KO) mice with a live vaccine containing the Enterobacteriaceae bacterium Escherichia coli strain BL21 revealed that the production of anti-E. coli and anti-α-Gal IgM and IgG was associated with high mortality of I. ricinus nymphs during feeding. However, this effect was absent in two different strains of wild type mice, BALB/c and C57BL/6. This result concurred with a wide distribution of α-1,3-galactosyltransferase genes, and possibly α-Gal, in Enterobacteriaceae and other bacteria of tick microbiota. Interestingly, the weight of I. ricinus nymphs that fed on E. coli-immunized C57BL/6 was significantly higher than the weight of ticks that fed on C57BL/6 immunized with a mock vaccine. Our results suggest that anti-tick microbiota vaccines are a promising tool for the experimental manipulation of vector microbiota, and potentially the control of ticks and tick-borne pathogens.

Anti-microbiota vaccines modulate the tick microbiome in a taxon-specific manner

“…Representative bacteria of the genera Escherichia - Shigella (i.e., E. coli ) and Leuconostoc (i.e., L. mesenteroides ) were selected to be included in live bacteria vaccine formulations, aiming to test the impact of host immune response against “keystone” bacteria on tick microbiota composition, stability and functionality, and tick performance. The selection of these bacteria as live vaccines was based on our previous results (16) that show that the family Enterobacteriaceae was among the top keystone taxa (i.e, high relative abundance, ubiquitousness, and eigencentrality) identified in Ixodes microbiota. Based on the previous results (16), we selected the family Leuconostocaceae as non-keystone bacteria with low “Keystoneness” (i.e, low relative abundance, ubiquitousness, and eigencentrality) in the microbiome of Ixodes .…”

“…The gram-negative bacterium E. coli BL21 (DE3, Invitrogen, Carlsbad, CA, USA) was prepared as previously described (16). Briefly, E. coli was grown on Luria Broth (LB, Sigma-Aldrich, St. Louis, MO, USA) at 37°C under vigorous agitation, washed with phosphate buffer saline (PBS) 10 mM NaH 2 PO 4 , 2.68 mM KCl, 140 mM NaCl, pH 7.2 (Thermo Scientific, Waltham, MA, USA), resuspended at 3.6 × 10 4 colony-forming unit (CFU)/mL, and homogenized using a glass homogenizer.…”

“…The levels of Abs reactive against bacterial proteins were measured in mice sera as previously reported (16). The 96-well ELISA plates (Thermo Scientific, Waltham, MA, USA) were coated with 0.5 µg/mL (100 µL/well) of E. coli or L. mesenteroides protein extracts and incubated for 2 h with 100 rpm shaking at RT.…”

“…The functional capacity of the tick microbiome is not equal to the overall number of its individual components, as microbial species strongly and frequently interact with one another and form a complex functional network (14), which can thus be considered as a fundamental unit in microbial communities of ticks. Therefore, the microbial co-occurrence network represents a useful approach to identify the keystoneness of taxa and the potential interactions within the functional networks (15,16). Understanding these microbe-microbe relationships is a critical step for predicting their holistic consequences on tick performance, physiology, and vector competence (13,14,16).…”

Questing microbioticks : Interactions of microbes, ticks, vertebrates, and the environment

“…Interestingly, a recent study investigated the suitability of anti-tick microbiota vaccines to control ticks and tick-borne pathogens. In the experiment, the anti-tick vaccine targeting Escherichia coli impacted I. ricinus performance during feeding (Mateos-Hernández et al, 2020).…”