Anaerobic chytrids

Voncken FGJ, Boxma B, van Hoek A, et al. 2002. A hydrogenosomal Fe-hydrogenase from the anaerobic chytrid Neocallimastix sp L2. Gene 284 103-12. 

Hackstein JHP, Baker SE, van Hellemond JJ, Tielens AGM (2007) Hydrogenosomes of Anaerobic Chytrids an Alternative Way to Adapt to Anaerobic Environments (in this volume). Springer, Heidelberg... 

The metabolism of anaerobic chytrids has not been studied in great detail, but it is known that most anaerobic chytrids studied so far produce formate, acetate, succinate, lactate and ethanol besides hydrogen and carbon dioxide when growing on cellulose, glucose or fructose as a carbon source (Julliand et al. 1998). Such a mixed acid fermentation is very similar to bacterial mixed acid fermentations that are, for example, well known for facultative anaerobic enteric bacteria, such as Escherichia coli. 

Many different data, which will be discussed below, are consistent with a mitochondrial origin of the hydrogenosomes of anaerobic chytrids their morphology, the mitochondrial-type targeting signals that are used to import proteins, the ADP/ATP carriers and mitochondrial-type chaperones, and all this supplemented by genomic analyses of separate hydrogenosomal proteins. 

Cytosolic enzymes with a mitochondrial ancestry from the anaerobic chytrid Piromyces sp. E2. Mol Microbiol 30 1017-1027... 

Akhmanova A, Voncken FGJ, Hosea KM, Harhangi H, Keltjens JT, den Camp HJMO, Vogels GD, Hackstein JHP (1999) A hydrogenosome with pyruvate formate-lyase anaerobic chytrid fungi use an alternative route for pyruvate catabolism. Mol Microbiol 32 1103-1114... 

Voncken F, Boxma B, Tjaden J, Akhmanova A, Huynen M, Verbeek F, Tielens AGM, Hafer-kamp I, Neuhaus HE, Vogels G, Veenhuis M, Hackstein JHP (2002a) Multiple origins of hydrogenosomes functional and phylogenetic evidence from the ADP/ATP carrier of the anaerobic chytrid Neocallimastix sp. Mol Microbiol 44 1441-1454... 

Hydrogenosomes of Anaerobic Chytrids an Alternative Way to Adapt to Anaerobic Environments... 

Fig. 7.5. Pyruvatetformate lyase (PFL) and not pyruvatetferredoxin oxidoreductase (PFO) is the key enzyme in the hydrogenosomal energy metabolism of the anaerobic chytrid of Piromyces sp. E2 (Akhmanova et al. 1999 Boxma et al. 2004). Hydrogen formation depends solely on malate it can become marginal under certain metabolic conditions. The relative fluxes through the pathways are indicated by the thickness of the arrows, which are proportional to the calculated fluxes in the presence of 0.3% fructose. Use of PFL instead of PFO allows the formation of reduced equivalents to be avoided. Consequently, chytrid hydrogenosomes excrete formate and acetate as end products of their energy metabolism. (From Boxma et al. 2004)...

Haferkamp I, Hackstein JHP, Voncken FGJ, Schmit G, Tjaden J (2002) Functional integration of mitochondrial and hydrogenosomal ADP/ATP carriers in the Escherichia coli membrane reveals different biochemical characteristics for plants, mammals and anaerobic chytrids. Eur J Biochem 269 3172-3181... 

Fig. 10.3). Thus, anaerobic chytrid fungi have secondarily lost their aerobic mitochondrial function in adaptation to their anaerobic life style.

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