Rapid Communication Complete circular DNA in the mitochondria-like organelles of Blastocystis hominis Ivan Wawrzyniak a,1 , Michae ¨l Roussel a,1 , Marie Diogon a , Arnaud Couloux b , Catherine Texier a , Kevin S.W. Tan c , Christian P. Vivare `s a , Fre ´de ´ric Delbac a , Patrick Wincker b , Hicham El Alaoui a, * a Laboratoire Microorganismes: Ge ´nome et Environnement, UMR CNRS 6023, Universite ´ Blaise Pascal, 63177 Aubie `re Cedex, France b Genoscope (CEA) and CNRS UMR 8030, Universite ´ d’Evry, 2 rue Gaston Cre ´mieux CP5706, 91057 Evry, France c Laboratory of Molecular and Cellular Parasitology, Department of Microbiology, Yong Loo Lin School of Medicine, National University of Singapore, 5 Science Drive 2, 117597, Singapore Received 23 April 2008; received in revised form 16 June 2008; accepted 17 June 2008 Abstract Blastocystis hominis is an anaerobic parasite of the human intestinal tract belonging to the Stramenopile group. Using genome sequencing project data, we describe here the complete sequence of a 29,270-bp circular DNA molecule that presents mitochondrial fea- tures (such as oxidative phosphorylation complex I subunits) but lacks complexes III, IV and V. Transmission electron microscopy anal- yses reveal that this molecule, as well as mitochondrial (NADH:ubiquinone oxidoreductase subunit 7 (NAD7), b-succinyl-CoA synthetase (b-SCS)) and hydrogenosomal (pyruvate ferredoxin oxido-reductase (PFOR), iron-hydrogenase) proteins, are located within double-membrane surrounded-compartments known as mitochondria-like organelles (MLOs). As there is no evidence for hydrogen pro- duction by this organism, we suggest that MLOs are more likely anaerobic mitochondria. Ó 2008 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. Keywords: Blastocystis hominis; MLOs; Circular DNA molecule; Iron-hydrogenase Stramenopiles (Patterson, 1999) constitute a highly diverse group that includes free photosynthetic organisms such as diatoms, as well as non-photosynthetic taxa such as plant (Phytophthora spp.) and animal (Blastocystis spp.) parasites. They can live either in aerobic or in anaer- obic conditions depending on their habitat (parasitic, fresh- water, marine or terrestrial). Blastocystis hominis is a common anaerobic protozoan parasite found in the intesti- nal tract of humans and animals, that has recently been suggested to be involved in Irritable Bowel Syndrome (Stark et al., 2007). It harbours double-membrane sur- rounded-organelles of about 1 lm, named ‘‘mitochon- dria-like organelles” (MLOs) (Nasirudeen and Tan, 2004), but their role and nature remain unclear. Most of the microorganisms that live in different microaerophilic or anaerobic environments (e.g. protists, fungi and para- sitic helminths), lack classical mitochondria but possess mitochondria-related organelles known as anaerobic mito- chondria, hydrogenosomes or mitosomes. The two former are still able to produce energy, however mitosomes have lost this property but retain the iron–sulfur cluster assem- bly machinery (Hackstein et al., 2006). Although the origin of these organelles is controversial, most evidence supports evolution from mitochondria (Embley and Martin, 2006). A recent analysis of a Blastocystis expressed sequence tag (EST) database notably blurs the distinction between mito- chondria and hydrogenosomes (Stechmann et al., 2008). Our present study reports the first data from the whole genome sequencing project of B. hominis that is currently running at the Genoscope (Evry, France). The sequenced isolate belonged to the subtype 7 according to Blastocystis nomenclature standardization (Stensvold et al., 2007). It 0020-7519/$34.00 Ó 2008 Australian Society for Parasitology Inc. Published by Elsevier Ltd. All rights reserved. doi:10.1016/j.ijpara.2008.06.001 * Corresponding author. Tel.: +33 4 73 40 74 31; fax: +33 4 73 40 76 70. E-mail address: hicham.el_alaoui@univ-bpclermont.fr (H. El Alaoui). 1 These authors made an equal contribution to the manuscript. www.elsevier.com/locate/ijpara Available online at www.sciencedirect.com International Journal for Parasitology 38 (2008) 1377–1382