Evolutionary Genetics of Borrelia

Abstract

The genus Borrelia consists of evolutionarily and genetically diverse bacterial species that cause a variety of diseases in humans and domestic animals. These vector-borne spirochetes can be classified into two major evolutionary groups, the Lyme borreliosis clade and the relapsing fever clade, both of which have complex transmission cycles during which they interact with multiple host species and arthropod vectors. Molecular, ecological, and evolutionary studies have each provided significant contributions towards our understanding of the natural history, biology and evolutionary genetics of Borrelia species; however, integration of these studies is required to identify the evolutionary causes and consequences of the genetic variation within and among Borrelia species. For example, molecular and genetic studies have identified the adaptations that maximize fitness components throughout the Borrelia lifecycle and enhance transmission efficacy but provide limited insights into the evolutionary pressures that have produced them. Ecological studies can identify interactions between Borrelia species and the vertebrate hosts and arthropod vectors they encounter and the resulting impact on the geographic distribution and abundance of spirochetes but not the genetic or molecular basis underlying these interactions. In this review we discuss recent findings on the evolutionary genetics from both of the evolutionarily distinct clades of Borrelia species. We focus on connecting molecular interactions to the ecological processes that have driven the evolution and diversification of Borrelia species in order to understand the current distribution of genetic and molecular variation within and between Borrelia species. and domestic animals (Burgdorfer et al., 1982;Parker and White, 1992;Pritt et al., 2016), please see Radolf and Samuels (2021). Species within the genus Borrelia are classified into two major evolutionary groups, the Lyme borreliosis clade (LB) and the relapsing fever clade (RF). Members of the Lyme borreliosis clade are vectored exclusively by hard-bodied ticks in the Ixodes genus and have been investigated to a much greater depth than members of the relapsing fever clade, most of which are vectored by soft-bodied Argasid ticks. Although these divergent evolutionary clades recently have been proposed as separate genera (Adeolu and Gupta, 2014), we will continue to refer to them as the Lyme borreliosis clade and the relapsing fever clade until the new classifications have additional consensus (Adeolu and Gupta, 2014;Barbour et al., 2017;Margos et al., 2017Margos et al., , 2020. In this article, we review t h e e c o l o g i c a l i n t e r a c t i o n s u n d e r l y i n g t h e evolutionary forces that have produced the current distribution of genetic and genomic variation in both the LB and RF Borrelia clades (Table 1). In addition, we focus on the evolutionary and ecological Curr. Issues Mol. Biol. 42: 97-112. caister.com/cimb caister.com/cimb 97 Curr. Issues Mol. Biol. Vol. 42 Evolutionary Genetics of Borrel...

Ecological and evolutionary perspectives on tick-borne pathogen co-infections

“…In addition, competition experiments between B. afzelii strains showed that strain interaction affects bacterial density and prevalence in immature I. ricinus ticks ( Genné et al., 2018 ). Considering that B. burgdorferi density within ticks positively correlates with the probability of transmission to vertebrate hosts ( Rego et al., 2014 ), it is expected that competition among co-infecting strains may reduce the evolutionary fitness of the subdominant strain ( Oppler et al, 2021 ). Competition among co-infecting strains could select for traits to suppress the growth of other strains or to escape suppression.…”

“…Competition among co-infecting strains could select for traits to suppress the growth of other strains or to escape suppression. However, there is no evidence that such traits have evolved in Borrelia and the evolutionary pressures that may produce them are currently unknown ( Oppler et al, 2021 ). Future research could investigate experimentally the selective pressures created by competition between co-infecting Borrelia strains and determine their relative evolutionary outcomes.…”

Molecular evidence of Borrelia spp. in bats from Córdoba Department, northwest Colombia

“…Pathogenic species of the genus Borrelia are zoonotic bacteria that cause emerging and re-emerging infectious diseases worldwide and constitute a major threat to public health [1]. This genus is composed of two welldefined monophyletic groups: the Borrelia burgdorferi sensu lato (Bb) complex, which cause Lyme borreliosis and are transmitted by hard ticks of the genus Ixodes, and borreliae of the relapsing fever (RF) group, transmitted mainly by soft ticks of the genus Ornithodoros, some species by ixodid ticks (e.g., Borrelia miyamotoi), and Borrelia recurrentis, transmitted by the clothing louse [2].…”

“…Most species of Borrelia have complex transmission cycles interacting with multiple vertebrate hosts and vector ticks [1]. For instance, several members of the order Rodentia are reservoir hosts [5,6].…”

FtlA and FtlB Are Candidates for Inclusion in a Next-Generation Multiantigen Subunit Vaccine for Lyme Disease

“…We refer to pathogenic Borreliella species collectively as the LD spirochetes. LD spirochetes are maintained in nature in an enzootic cycle involving Ixodes species ticks and diverse vertebrate reservoirs ( 5 , 6 ). The CDC reported in 2016 that Ixodes scapularis and Ixodes pacificus ticks, the primary vectors for LD in North America, are present in 49.2% of United States counties ( 7 ).…”