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.
The 16S ribosomal DNA sequences of endosymbionts from the trypanosomatid protozoa (Crithidia spp.) are most homologous to that of Bordetella spp. This finding extends the polyphyletic origin of endosymbionts for the first time to the beta Proteobacteria. Biased base transitions and compensatory mutations of the symbionts' sequences that may contribute to their identity in the three Crithidia spp. are noted.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.