The Road to Hydrogenosomes

Recent studies increasingly support the hypothesis that organelles originating from the mitochondrial endosymbiotc event comprise a family of diverse structures and not only the typical mitochondria, with their characteristic cristate structure functioning as aerobic powerhouses of cells. This large family is regarded today to encompass a broad, almost continuous spectrum of organelles, from the much-studied typical aerobic mitochondria, through anaerobic mitochondria and hydrogenosomes to the stillenigmatic mitosomes. It is becoming generally accepted that these organelles evolved from a common ancestral organelle that arose in a single endosymbiotic event sometime during the emergence of the eukaryotic cell, as we know it today. Contributions to this volume explore the diverse members of this organelle family in detail and most of them also give a glimpse of the intense debates on the evolutionary origins of these organelles and their current impact on general hypotheses on the origin and evolutionary diversification of eukaryotes. One of the key contributions leading to the prevalent current views was the discovery of hydrogenosomes in certain “anaerobic” flagellates in the early 1970s. Initially they were regarded as an oddity or aberration and it took time before they were seriously discussed outside the community of protistologists. They remained an enigma until their mitochondrial relationships received strong support in the 1990s. Recent developments overshadow the early days of hydrogenosomes, as they indeed should. This volume, presenting an exciting collection of papers on mitochondrial diversity and evolution, is perhaps the appropriate place to retell briefly those early days by someone who was there. I eagerly accepted the suggestion of my friend, the coeditor of this volume, Bill Martin, that I do this. Needless to say, this will be an intensely personal history and certainly not an autobiography. Since the contributions to this volume provide a clear picture of later developments, I restrict my story to the very early days, approximately the first 12 years after the discovery of hydrogenosomes (Lindmark and Müller 1973). 1 The Road to Hydrogenosomes