Our research group is interested in parasitic and free-living anaerobic protists. We study the evolution, biogenesis, and function of their unusual organelles, particularly mitochondria and peroxisomes. The specific character of these organelles reflects (i) the adaptation of protists to life in oxygen-poor environments and (ii) their adaptation to parasitism. Our discovery of FeS cluster assembly machinery of mitochondrial type in hydrogenosomes of Trichomonas vaginalis and mitosomes of Giardia intestinalis provided strong arguments for the mitochondrial origin of these organelles. This view was further supported by the identification of remnant respiratory complex I and the characterization of protein import machinery in hydrogenosomes. Recently we have discovered a new type of peroxisomes that are present in hydrogenosome-bearing anaerobic free-living Mastigamoeba balamuthi and its parasitic relative Entamoeba histolytica. Another important part of our research is the investigation of virulence factors of Trichomonas vaginalis that are critical for the establishment of infection and disease development. We demonstrated that endosymbiotic Trichomonasvirus is released from trichomonads in exosomes and contribute to proinflammatory host cell response.