Lipids are the preferred substrate of the protistNaegleria gruberi, relative of a human brain pathogen

SUMMARYNaegleria gruberiis a free-living non-pathogenic amoeboflagellate and relative ofNaegleria fowleri, a deadly pathogen causing primary amoebic meningoencephalitis (PAM). A genomic analysis ofN. gruberiexists, but physiological evidence for its core energy metabolism orin vivogrowth substrates is lacking. Here we show thatN. gruberitrophozoites need oxygen for normal functioning and growth and that they furthermore shun both glucose and amino acids as growth substrates. Trophozoite growth depends mainly upon lipid oxidation via a mitochondrial branched respiratory chain, both ends of which require oxygen as final electron acceptor. GrowingN. gruberitrophozoites thus have a strictly aerobic energy metabolism with a marked substrate preference for the oxidation of fatty acids. Analyses ofN. fowlerigenome data and comparison with those ofN. gruberiindicate thatN. fowlerihas the same type of metabolism. Specialization to oxygen-dependent lipid breakdown represents a hitherto unprecedented metabolic strategy in protists.