The anaerobic chytridiomycete fungus Piromyces sp. E2 produces ethanol via pyruvate:formate lyase and an alcohol dehydrogenase E.
Anaerobic chytridiomycete fungi possess hydrogenosomes, which generate hydrogen and ATP, but also acetate and formate as end-products of a prokaryotic-type mixed-acid fermentation. Notably, the anaerobic chytrids Piromyces and Neocallimastix use pyruvate:formate lyase (PFL) for the catabolism of pyruvate, which is in marked contrast to the hydrogenosomal metabolism of the anaerobic parabasalian flagellates Trichomonas vaginalis and Tritrichomonas foetus, because these organisms decarboxylate pyruvate with the aid of pyruvate:ferredoxin oxidoreductase (PFO). Here, we show that the chytrids Piromyces sp. E2 and Neocallimastix sp. L2 also possess an alcohol dehydrogenase E (ADHE) that makes them unique among hydrogenosome-bearing anaerobes. We demonstrate that Piromyces sp. E2 routes the final steps of its carbohydrate catabolism via PFL and ADHE: in axenic culture under standard conditions and in the presence of 0.3% fructose, 35% of the carbohydrates were degraded in the cytosol to the end-products ethanol, formate, lactate and succinate, whereas 65% were degraded via the hydrogenosomes to acetate and formate. These observations require a refinement of the previously published metabolic schemes. In particular, the importance of the hydrogenase in this type of hydrogenosome has to be revisited.
Department of Evolutionary Microbiology, Faculty of Science, University of Nijmegen, Toernooiveld 1, NL-6525 ED Nijmegen, The Netherlands.
Brigitte
B
Boxma
Frank
F
Voncken
Sander
S
Jannink
Theo
T
van Alen
Anna
A
Akhmanova
Susanne W H
SW
van Weelden
Jaap J
JJ
van Hellemond
Guenola
G
Ricard
Martijn
M
Huynen
Aloysius G M
AG
Tielens
Johannes H P
JH
Hackstein
D000123:Acetyltransferases / Q000378:metabolism*; D000426:Alcohol Dehydrogenase / Q000235:genetics / Q000378:metabolism*; D000595:Amino Acid Sequence; D003001:Cloning, Molecular; D004734:Energy Metabolism; D000431:Ethanol / Q000378:metabolism*; D005285:Fermentation; D005656:Fungal Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010802:Phylogeny; D020089:Piromyces / Q000201:enzymology*; D016415:Sequence Alignment
D005656:Fungal Proteins; D000431:Ethanol; D000426:Alcohol Dehydrogenase; D000123:Acetyltransferases; C022560:formate C-acetyltransferase