Phylogenetic relationship between the endosymbiont “Candidatus Riesia pediculicola” and its human louse host

Abstract

Background The human louse (Pediculus humanus) is a haematophagous ectoparasite that is intimately related to its host. It has been of great public health concern throughout human history. This louse has been classified into six divergent mitochondrial clades (A, D, B, F, C and E). As with all haematophagous lice, P. humanus directly depends on the presence of a bacterial symbiont, known as “Candidatus Riesia pediculicola”, to complement their unbalanced diet. In this study, we evaluated the codivergence of human lice around the world and their endosymbiotic bacteria. Using molecular approaches, we targeted lice mitochondrial genes from the six diverged clades and Candidatus Riesia pediculicola housekeeping genes. Methods The mitochondrial cytochrome b gene (cytb) of lice was selected for molecular analysis, with the aim to identify louse clade. In parallel, we developed four PCR primer pairs targeting three housekeeping genes of Candidatus Riesia pediculicola: ftsZ, groEL and two regions of the rpoB gene (rpoB-1 and rpoB-2). Results The endosymbiont phylogeny perfectly mirrored the host insect phylogeny using the ftsZ and rpoB-2 genes, in addition to showing a significant co-phylogenetic congruence, suggesting a strict vertical transmission and a host–symbiont co-speciation following the evolutionary course of the human louse. Conclusion Our results unequivocally indicate that louse endosymbionts have experienced a similar co-evolutionary history and that the human louse clade can be determined by their endosymbiotic bacteria. Graphical Abstract

Genome-wide analysis of the human head louse (Pediculus humanus capitis) reveals geographically structured genetic populations

“…If mtDNA saturation is at play, which can happen due to the rapid evolutionary rate, mtDNA markers could be inaccurately signaling to this deep louse evolutionary history. This seems unlikely, however, because the primary endosymbiont of lice, Candidatus Riesia pediculicola , which is maternally inherited, shows similar distribution patterns to louse mitochondrial DNA (Hammoud et al, 2022) .…”

Genomic Diversity in the Endosymbiotic Bacteria of Human Head Lice

“…Like many insect parasites, lice are host to maternally inherited endosymbiotic bacteria, Candidatus Riesia pediculicola (Gammaproteobacteria: Enterobacterales). These endosymbiotic bacteria provide the lice with essential B-vitamins, which the lice cannot obtain from human blood in sufficient quantities to sustain development ( Puchta 1955 ; Buchner 1965 ; Koch 1967 ; Eberle and McLean 1982 , 1983 ; Sasaki-Fukatsu et al 2006 ; Perotti et al 2007 ; Boyd et al 2017 ; Hammoud et al 2022 ). Ca .…”