Monophyletic origin of beta-division proteobacterial endosymbionts and their coevolution with insect trypanosomatid protozoa Blastocrithidia culicis and Crithidia spp.

Abstract

Some trypanosomatid protozoa (order Kinetoplastida) are well known to harbor bacterial endosymbionts.Their phylogenetic positions and evolutionary relationships with the hosts were deduced by comparing the rRNA gene sequences. Earlier, we observed that these symbionts from three Crithidia spp. are identical and are closely related to BordeteUa bronchiseptica. We have now sequenced the genes of another endosymbiont and the host protozoan Blastocrithidia culicis. The 16S rRNA genes of the Blastocrithidia and Crithidia symbionts share =-97% identity and form a distinct group, branching off the B. bronchiseptica lineage in the 3-division of Proteobacteria. Comparison of their secondary structures in the stem regions suggests compensatory mutations of the symbiont sequences, contributing to their biased base transitions from G to A and C to T. Two putative genes encoding tRNAne and tRNAh are highly conserved in the otherwise variable internal transcribed spacer region. Comparisons of the host rRNA gene sequences suggest that the symbiontcontaining Crithidia and Blastocrithidia are more akin to each other than to other trypanosomatids. The evidence suggests that Blastocrithdia and COthidia symbionts descend from a common ancestor, which had presumably entered an ancestral host and thence coevolved with it into different species. We therefore propose naming the symbionts Kinetoplastbactetoum blastocrithid and Kinetoplastbateoium crhi.

Cryptic Paraflagellar Rod in Endosymbiont-Containing Kinetoplastid Protozoa

“…It is worth noting that the PFR1 phylogeny shown here agrees with those inferred from other molecular data (14,20) in supporting the monophyly of the endosymbiont-bearing species (as would be expected for a rare event such as enslavement). Our phylogeny, in common with the rRNA data (20), also suggests that non-endosymbiont-bearing Crithidia species diverged from those possessing an endosymbiont soon after the divergence of the leishmanial and trypanosomal lines and that the nomenclature of the kinetoplastids often does not reflect evolutionary relatedness (for example, the genera Crithidia and Herpetomonas encompass both endosymbiontbearing and endosymbiont-lacking species and are not monophyletic taxa).…”

Comparison and Evolutionary Analysis of the Glycosomal Glyceraldehyde-3-Phosphate Dehydrogenase from Different Kinetoplastida

“…All rooted trees suggest that T. brucei and T. cruzi diverged before the lineage leading to Crithidia, Leishmania, and other trypanosomatid genera which are closely related. However, depending on the number, the origin, or the alignment of the sequences, the genus Trypanosoma appears to be either paraphyletic (Gomez et al 1991;Fernandes et al 1993;Landweber and Gilbert 1994;Maslov et al 1994Maslov et al , 1996Du et al 1994;Lukes et al 1994) or monophyletic (Hernandez et al 1990;Berchtold et al 1994;Marche et al 1995). Recently, Lukes et al (1997) suggested that the paraphyletic tree topology may be an artifact caused by a high rate of substitutions in the rRNA genes of the T. brucei and outgroup lineages.…”

Analysis of Ribosomal RNA Genes Suggests That Trypanosomes Are Monophyletic

“…Subsequently, nuclear small and large subunit (SSU and LSU, respectively) rRNA gene sequences were used to infer the phylogeny of kinetoplastids (Gomez et al 1991;Fernandes et al 1993;Landweber and Gilbert 1994;Maslov et al , 1996Du et al 1994). These trees were rooted with outgroup sequences from Euglena gracilis; a bodonid, Bodo caudatus; and a cryptobiid, Trypanoplasma borreli.…”