The Tick Microbiome: The "Other Bacterial Players" in Tick Biocontrol

Abstract

Hard ticks (family Ixodidae) are one of the most predominant arthropod disease vectors worldwide, second only to mosquitoes. In addition to harboring animal and human pathogens, ticks are known to carry a microbial community constituted of non-pathogenic organisms, which includes maternally inherited intracellular endosymbionts and other environmentally acquired extracellular microorganisms. These microbial communities, which include bacteria, viruses, protozoans, and fungi-with often commensal, mutualistic, or parasitic associations with the tick-comprise the tick microbiome, bacteria being the most studied community. Many bacterial taxa frequently reported in ticks include soil, plant, and animal-associated microbes, suggesting many are environmentally acquired, including members with known entomopathogenic potential, such as Bacillus thuringiensis, Bacillus spp., and Pseudomonas spp. It has been reported that microbial community composition can impact pathogen persistence, dissemination, and fitness in ticks. In the United States, Ixodes scapularis (northeast) and I. pacificus (west) are the predominant vectors of Borrelia burgdorferi, the causal agent of Lyme disease. Amblyomma americanum is another important tick vector in the U.S. and is becoming an increasing concern as it is the leading cause of alpha-gal syndrome (AGS, or red meat allergy). This condition is caused by tick bites containing the galactose alpha 1,3 galactose (alpha-gal) epitope in their saliva. In this paper, we present a summary of the tick microbiome, including the endosymbiotic bacteria and the environmentally acquired (here referred to as the non-endosymbiotic community). We will focus on the non-endosymbiotic bacteria from Ixodes spp. and Amblyomma americanum and discuss their potential for novel biocontrol strategies.

Keywords: Ixodes spp.; amblyomma americanum; bacillus; bacillus thuringiensis; tick biocontrol; tick microbiome.

Figure 1

The tick microbiome and its environment. In addition to maternally inherited endosymbionts, the tick microbiome comprises environmentally acquired microorganisms from the soil, plants, and water droplets (left), while pathogens and the host’s skin-associated microorganisms are acquired through feeding (right). These microbial communities interact with the tick midgut immune system. It is yet unknown to what extent the acquired organisms interact with the tick endosymbionts. The illustration was created and edited using Adobe Illustrator “adobe.com/products/illustrator”; 2019; (accessed on 27 September 2024), Adobe Sketch “www.adobe.com” (accessed on 10 October 2024), Adobe Stock “https://stock.adobe.com” (accessed 10 October 2024), and PowerPoint.