Phylogenetic and structural characterization of Kentomonas inusitatus n. sp.: Unique insect trypanosomatid of the Strigomonadinae subfamily naturally lacking bacterial endosymbiont

All insect trypanosomatids of the subfamily Strigomonadinae harbor a proteobacterial symbiont in their cytoplasm and unique ultrastructural cell organization. Here, we report an unexpected finding within the Strigomonadinae subfamily: the identification of a new species lacking bacterial symbiont, represented by two isolates obtained from Calliphoridae flies in Brazil and Uganda. This species is hereby designated as Kentomonas inusitatus n. sp. Molecular investigations targeting symbiont DNA, cell proliferation, and ultrastructural analyses agreed with the absence of bacterial symbionts in cultured flagellates. PCR-screening specifically targeting symbiont DNA corroborated the absence of symbionts in K. inusitatus present in the intestine of the respective host flies. K. inusitatus exhibited forms varying in size and shape. While displaying overall ultrastructural features of the Strigomonadinae, the novel species showed mitochondrial branches juxtaposed to the plasma membrane in locations both without and notable, with subpellicular microtubules. The discovery of the first Strigomonadinae species naturally lacking a symbiont and closely related to K. sorsogonicus, suggests a unique evolutionary history for the genus Kentomonas. Our findings provide novel insights into the complex relationships between trypanosomatids and their symbionts.