Crithidia Leger 1902

Introduction

Within the last 100 years, the genera Leptomonas, Crithidia, Blastocrithidia, Wallaceina and Herpetomonas have been described based on the presence and/or combination of morphs in their life cycles. Some insect trypanosomatids contain a bacterial endosymbiont in their cytoplasm, which divides synchronously with the host cell (de Souza and Motta 1999). Aposymbiotic strains can be obtained by treatment of insect trypanosomatids with antibiotics. The presence of the endosymbiont is associated with morphological changes, such as a cryptic paraflagellar rod (Gadelha et al., 2005).  However, recent careful investigations of numerous new species isolated from insects showed that the taxonomy based on morphology is invalid for several reasons:

1. there is much higher variability in morphology of a given species than anticipated
2. for a given species, different stages can be found in the host and in the culture
3. molecular phylogeny showed that none of these genera represents a monophyletic assembly of species.

Therefore, sequence data derived from conserved genes such as GAPDH, SL RNA and 18S rRNA should be used as main criteria for improved systematics of the insect trypanosomatids (Yurchenko et al., 2006; 2008). Until this work has been done, it is not clear whether the species currently placed in the genus Crithidia form a monophyletic group.

References

De Souza W. and M.C.M. Motta. 1999. Endosymbiosis in protozoa of the Trypanosomatidae family. FEMS Microbiol. Lett. 173: 1-8.

Gadelha C., B. Wickstead, W. de Souza, K. Gull and N. Cunha-e-Silva. 2005. Cryptic paraflagellar rod in endosymbiont-containing kinetoplastid protozoa. Eukaryot. Cell 4: 516-525.

Yurchenko V., J. Lukeš, X. Xu and D.A. Maslov. 2006. An integrated morphological and molecular approach to a new species description in the Trypanosomatidae: the case of Leptomonas podlipaevi n.sp., a parasite of Boisea rubrolineata (Hemiptera: Rhopalidae). J. Euk. Microbiol. 53: 103-111.

Yurchenko V.A., J. Lukeš, M. Tesařová, M. Jirků and D.A. Maslov. 2008. Morphological discordance of the new trypanosomatid species phylogenetically associated with the genus Crithidia. Protist 159: 99-114.