A Nonmitochondrial hydrogen production in naegleria gruberi

Abstract

Naegleria gruberi is a free-living heterotrophic aerobic amoebawell known for its ability to transform from an amoeba to a flagellate form. Thegenomeof N. gruberi hasbeen recently published,and insilicopredictionsdemonstrated that Naegleria has thecapacity for both aerobic respiration and anaerobic biochemistry to producemolecular hydrogen in itsmitochondria. This findingwas considered to have fundamental implications on the evolution of mitochondrial metabolism and of the last eukaryotic common ancestor. However, no actual experimental data have been shown to support this hypothesis. For this reason, we have decided to investigate the anaerobicmetabolismof the mitochondrion of N. gruberi.Usingin vivobiochemical assays,wehavedemonstrated thatN. gruberi has indeed a functional [FeFe]-hydrogenase, an enzyme that is attributed to anaerobic organisms. Surprisingly, in contrast to the published predictions, we have demonstrated that hydrogenase is localized exclusively in the cytosol, while no hydrogenase activity was associated with mitochondria of the organism. In addition, cytosolic localization displayed for HydE, a marker component of hydrogenasematurases. Naegleria gruberi, an obligate aerobic organismand one of the earliest eukaryotes, is producing hydrogen, a function that raises questions on the purpose of this pathway for the lifestyle of the organism and potentially on the evolution of eukaryotes. © 2014 The Author(s).