The genus Borrelia reloaded

Abstract

The genus Borrelia, originally described by Swellengrebel in 1907, contains tick- or louse-transmitted spirochetes belonging to the relapsing fever (RF) group of spirochetes, the Lyme borreliosis (LB) group of spirochetes and spirochetes that form intermittent clades. In 2014 it was proposed that the genus Borrelia should be separated into two genera; Borrelia Swellengrebel 1907 emend. Adeolu and Gupta 2014 containing RF spirochetes and Borreliella Adeolu and Gupta 2014 containing LB group of spirochetes. In this study we conducted an analysis based on a method that is suitable for bacterial genus demarcation, the percentage of conserved proteins (POCP). We included RF group species, LB group species and two species belonging to intermittent clades, Borrelia turcica Güner et al. 2004 and Candidatus Borrelia tachyglossi Loh et al. 2017. These analyses convincingly showed that all groups of spirochetes belong into one genus and we propose to emend, and re-unite all groups in, the genus Borrelia.

Fig 1. Phylogenetic reconstruction of Borrelia species based on 791 aligned protein homologs built with the PEPR pipeline and FastTree2 with 100 jackknifed resampling replicates.

All node support values are 100 except where indicated.

Fig 2. Boxplot of inter- and intra-specific POCP values.

Inter-specific and intra-specific comparisons included Lyme borreliosis (LB) and relapsing-fever species (RF), reptile-associated species (REP) including the echnida-associated species ‘Candidatus B. tachyglossi’. The inter-genera comparison included the members of the genera Borrelia, Brachyspira, Leptospira, Spirochaeta, and Treponema.

Fig 3. Percentage of conserved proteins (POCP) matrix generated by the method described in [18].

POCP values of species belonging to the LB group, RF group of spirochetes, the reptile-associated species B. turcica and echnida-associated species B. tachyglossi are above the genus threshold of 50%, indicating that all belong into one bacterial genus, Borrelia.

Fig 4

Partial amino acid alignment of (A) a putative lipoprotein (GI: 1195064) and (B) a hypothetical protein (GI: 1194969) showing a CSI in which the form of the indel in ‘Candidatus Borrelia tachyglossi’ and B. turcica matches that in LB species.