Effects of tetracycline treatment on the composition of the bacterial microbiota of Amblyomma aureolatum eggs and larvae

• Grant number: 25/12732-3
• Support Opportunities: Scholarships abroad - Research Internship - Doctorate
• Start date: October 01, 2025
• End date: December 31, 2025
• Field of knowledge: Biological Sciences - Parasitology - Entomology and Malacology of Parasites and Vectors
• Principal Investigator: Andréa Cristina Fogaça
• Grantee: Solange Cristina Antão
• Supervisor: Olivier Duron
• Host Institution: Instituto de Ciências Biomédicas (ICB). Universidade de São Paulo (USP). São Paulo , SP, Brazil
• Institution abroad: Université Montpellier 2, France
• Associated to the scholarship: 22/09055-1 - Determination of the role of the microbiota in the fitness of Amblyomma aureolatum ticks and in the acquisition and transmission of Rickettsia rickettsii, BP.DR

Abstract

In addition to carrying pathogens, ticks also harbor commensal and mutualistic microorganisms, which may be either obligate or facultative. Recent studies showed that alterations in tick microbiota composition may influence fitness and alter pathogen acquisition, facilitating or hindering colonization. In Brazil, Amblyomma sculptum and Amblyomma aureolatum are vectors of Rickettsia rickettsii, the causative agent of Brazilian spotted fever (BSF). This disease presents high lethality rates, reaching up to 70% in São Paulo state. Although both species are important in the transmission of R. rickettsii, A. sculptum is much less susceptible to infection than A. aureolatum. A previous study of our research group showed that while A. sculptum has a very reduced microbiota, A. aureolatum harbors an abundant microbiota, mostly composed of bacteria of the Francisella genus. To evaluate the role played by microbiota in the acquisition of R. rickettsii, A. aureolatum engorged females were treated with tetracycline. As a control, females were treated only with sterile PBS. A significant reduction of the bacterial load and the levels of antimicrobial peptide transcripts was observed in the eggs laid by antibiotic-treated females in comparison to the control, which was followed by a higher acquisition of R. rickettsii by hatched larvae. The antibiotic treatment also exerted a negative effect on the tick development, decreasing the molt efficiency of larval to nymphal stage. These results suggest that the maternal microbiota plays a role in shaping offspring immunity, pathogen susceptibility, and tick development. Therefore, the current project aims to determine the taxonomic composition of the bacterial microbiota of eggs and larvae derived from tetracycline-treated and control females by next generation sequencing (NGS) of the bacterial 16S rRNA gene to better understand how specific microbial communities may influence vector-pathogen interactions and tick physiology. The dataset of samples from treated group will be compared to the dataset of control group from the same stage (eggs or larvae). For the statistical analysis of alpha diversity, the Shannon and Faith's Phylogenetic Diversity (Faith-PD) indices will be used. Beta diversity will be assessed using the Bray-Curtis index. Additionally, Principal Coordinates Analysis (PCoA) will be performed to compare distance matrices between samples, and their significance will be evaluated using the PERMANOVA test. Differences will be considered significant when p < 0.05. (AU)