The catalase gene is a virtually ubiquitous component of the eukaryotic genomes. It is also present in the monoxenous (i.e. parasitizing solely insects) trypanosomatids of the subfamily Leishmaniinae, which have acquired the enzyme by horizontal gene transfer from a bacterium. However, as shown here, the catalase gene was secondarily lost from the genomes of all Leishmania sequenced so far. Due to the potentially key regulatory role of hydrogen peroxide in the inter-stagial transformation of Leishmania spp., this loss seems to be a necessary prerequisite for the emergence of a complex life cycle of these important human pathogens. Hence, in this group of protists, the advantages of keeping catalase were uniquely outweighed by its disadvantages.

Biology Centre Institute of Parasitology Czech Academy of Sciences 370 05 České Budějovice Czech Republic

Biology Centre Institute of Parasitology Czech Academy of Sciences 370 05 České Budějovice Czech Republic; Canadian Institute for Advanced Research Toronto Ontario M5G 1Z8 Canada

Biology Centre Institute of Parasitology Czech Academy of Sciences 370 05 České Budějovice Czech Republic; Department of Biochemistry University of Cambridge Cambridge CB2 1GA United Kingdom

Life Science Research Centre Faculty of Science University of Ostrava 710 00 Ostrava Czech Republic

Life Science Research Centre Faculty of Science University of Ostrava 710 00 Ostrava Czech Republic; Biology Centre Institute of Parasitology Czech Academy of Sciences 370 05 České Budějovice Czech Republic; Institute of Environmental Technologies Faculty of Science University of Ostrava 710 00 Ostrava Czech Republic

Life Science Research Centre Faculty of Science University of Ostrava 710 00 Ostrava Czech Republic; Zoological Institute of the Russian Academy of Sciences St Petersburg 199034 Russia

References provided by Crossref.org

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