Evolution Anaerobic peroxisome in Mastigamoeba balamuthi

Adaptation of eukaryotic cells to anaerobic condition is reflected by deep changes in mitochondrial metabolism and their functional reduction. The most modified types of mitochondria are hydrogenosomes that generate molecular hydrogen with concomitant ATP synthesis and mitosome that completely lost energy metabolism. The reduction of mitochondria is associated with loss of peroxisomes that evolved from ER to compartmentalize pathways generating reactive oxygen species (ROS) and thus prevent cellular oxidative damage. Biogenesis and function of peroxisomes is tightly coupled with mitochondria. They share the fission machinery, pathways of oxidative metabolism, ROS scavenging, and metabolic products. The loss of peroxisomes in anaerobic eukaryotes with reduced mitochondria is thus not unexpected. Surprisingly, we identified peroxisomes in anaerobic, hydrogenosome bearing protist Mastigamoeba balamuthi. Initially, we identified conserved set of peroxisomal proteins peroxins that are required for protein import, peroxisomal growth and division. Key membrane associated peroxins (MbPex3, MbPex11, and MbPex14) were visualized in numerous vesicles that were distinct from hydrogenosomes, ER and Golgi body. Proteomic analysis of cellular fractions and prediction of peroxisomal targeting signals (PTS1/PTS2) allows identification of 51 putative peroxisomal matrix proteins. Expression of selected proteins in Saccharomyces cerevisiae revealed that they are specifically targeted to yeast peroxisomes. Matrix protein includes components of acyl CoA and carbohydrate metabolism, pyrimidine and CoA biosynthesis, whereas neither components of β-oxidation nor catalase were present. In conclusion, we identified new subclass of peroxisomes named “anaerobic” peroxisome that shifts the current paradigm and rises attention to reductive evolution of peroxisomes in anaerobic organisms.