Ds. Horner et al., A single eubacterial origin of eukaryotic pyruvate : ferredoxin oxidoreductase genes: Implications for the evolution of anaerobic eukaryotes, MOL BIOL EV, 16(9), 1999, pp. 1280-1291
The iron sulfur protein pyruvate:ferredoxin oxidoreductase (PFO) is central
to energy metabolism in amitochondriate eukaryotes, including those with h
ydrogenosomes. Thus, revealing the evolutionary history of PFO is critical
to understanding the origin(s) of eukaryote anaerobic energy metabolism. We
determined a complete PFO sequence for Spironucleus barkhanus, a large fra
gment of a PFO sequence from Clostridium pasteurianum, and a fragment of a
new PFO from Giardia lamblia. Phylogenetic analyses of eubacterial and euka
ryotic PFO genes suggest a complex history for PFO, including possible gene
duplications and horizontal transfers among eubacteria. Our analyses favor
a common origin for eukaryotic cytosolic and hydrogenosomal PFOs from a si
ngle eubacterial source, rather than from separate horizontal transfers as
previously suggested. However, with the present sampling of genes and speci
es, we were unable to infer a specific eubacterial sister group for eukaryo
tic PFO. Thus, we find no direct support for the published hypothesis that
the donor of eukaryote PFO was the common alpha-proteobacterial ancestor of
mitochondria and hydrogenosomes. We also report that several fungi and pro
tists encode proteins with PFO domains that are likely monophyletic with PF
Os from anaerobic protists. In Saccharomyces cerevisiae, PFO domains combin
e with fragments of other redox proteins to form fusion proteins which part
icipate in methionine biosynthesis. Our results are consistent with the vie
w that PFO, an enzyme previously considered to be specific to energy metabo
lism in amitochondriate protists, was present in the common ancestor of con
temporary eukaryotes and was retained, wholly or in part, during the evolut
ion of oxygen-dependent and mitochondrion-bearing lineages.