A hydrogenosome with pyruvate formate-lyase: anaerobic chytrid fungi use an alternative route for pyruvate catabolism

The chytrid fungi Piromyces sp. E2 and Neocallimastix sp. L2 are obligatory amitochondriate anaerobes that possess hydrogenosomes. Hydrogenosomes are highly specialized organelles engaged in anaerobic carbon metabolism; they generate molecular hydrogen and ATP. Here, we show for the first time that chytrid hydrogenosomes use pyruvate formate-lyase (PFL) and not pyruvate:fe rredoxin oxidoreductase (PFO) for pyruvate catabolism, unlike all other hyd rogenosomes studied to date. Chytrid PFLs are encoded by a multigene family and are abundantly expressed in Piromyces sp. E2 and Neocallimastix sp. L2 , Western blotting after cellular fractionation, proteinase K protection as says and determinations of enzyme activities reveal that PFL is present in the hydrogenosomes of Piromyces sp. E2. The main route of the hydrogenosoma l carbon metabolism involves PFL; the formation of equimolar amounts of for mate and acetate by isolated hydrogenosomes excludes a significant contribu tion by PFO. Our data support the assumption that chytrid hydrogenosomes ar e unique and argue for a polyphyletic origin of these organelles.