The establishment of the mitochondrion is seen as a transformational step in the origin of eukaryotes. With the mitochondrion came bioenergetic freedom to explore novel evolutionary space leading to the eukaryotic radiation known today. The tight integration of the bacterial endosymbiont with its archaeal host was accompanied by a massive endosymbiotic gene transfer resulting in a small mitochondrial genome which is just a ghost of the original incoming bacterial genome. This endosymbiotic gene transfer resulted in the loss of many genes, both from the bacterial symbiont as well the archaeal host. Loss of genes encoding redundant functions resulted in a replacement of the bulk of the host's metabolism for those originating from the endosymbiont. Glycolysis is one such metabolic pathway in which the original archaeal enzymes have been replaced by bacterial enzymes from the endosymbiont. Glycolysis is a major catabolic pathway that provides cellular energy from the breakdown of glucose. The glycolytic pathway of eukaryotes appears to be bacterial in origin, and in well-studied model eukaryotes it takes place in the cytosol. In contrast, here we demonstrate that the latter stages of glycolysis take place in the mitochondria of stramenopiles, a diverse and ecologically important lineage of eukaryotes. Although our work is based on a limited sample of stramenopiles, it leaves open the possibility that the mitochondrial targeting of glycolytic enzymes in stramenopiles might represent the ancestral state for eukaryotes.

Biosciences University of Exeter United Kingdom

Département de Biochimie Université de Montréal C P 6128 Montréal Quebec Canada

Department of Biochemistry and Molecular Biology Dalhousie University Halifax Canada

Department of Chemistry and Physical Sciences Pace University

Fachbereich Biologie Universität Konstanz Germany

Institut für Genetik Technische Universität Braunschweig

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

Institute of Parasitology University of Zürich Switzerland

Leibniz Institut DSMZ Deutsche Sammlung von Mikroorganismen und Zellkulturen GmbH Braunschweig Germany

Rangos Research Center University of Pittsburgh Children's Hospital Pittsburgh PA

School of Biological Sciences University of Bristol United Kingdom

School of Science and Human Gut Microbiome for Health Research Unit Mae Fah Luang University Chiang Rai Thailand

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