Genetic evidence points to an evolutionary link between hydrogenosomes – organelles found in some ciliates, trichomonads, and fungi that generate hydrogen and ATP – and mitochondria,¹ according to Dutch and German researchers led by Johannes Hackstein of Radboud University Nijmegen in the Netherlands.

The team performed long-range PCR on hydrogenosome DNA from Nyctotherus ovalis, a ciliate found in the hindgut of American cockroaches. It yielded a 12-kilobase fragment of the organellar genome that encodes four genes of a mitochondrial complex I (nad2, nad4L, nad5, and nad7), two genes encoding mitochondrial ribosomal proteins (rpl2 and rpl14), and a tRNA tyrosine gene.

Investigating N. ovalis, the researchers identified three additional mitochondrial I complex genes in its nucleus, for a total of seven of the 14 core genes needed for that complex. They also found genes for half of the proteins of mitochondrial...