Multiple origins of hydrogenosomes:functional and phylogenetic evidence from the ADP/ATP carrier of the anaerobic chytrid Neocallimastix sp.

A mitochondrial-type ADP/ATP carrier (AAC) has been identified in the hydrogenosomes of the anaerobic chytridiomycete fungus Neocallimastix sp. L2. Biochemical and immunocytochemical studies revealed that this ADP/ATP carrier is an integral component of hydrogenosomal membranes. Expression of the corresponding cDNA in Escherichia coli confers the ability on the bacterial host to incorporate ADP at significantly higher rates than ATP - similar to isolated mitochondria of yeast and animals. Phylogenetic analysis of this AAC gene (hdgaac ) confirmed with high statistical support that the hydrogenosomal ADP/ATP carrier of Neocallimastix sp. L2 belongs to the family of veritable mitochondrial-type AACs. Hydrogenosome-bearing anaerobic ciliates possess clearly distinct mitochondrial-type AACs, whereas the potential hydrogenosomal carrier Hmp31 of the anaerobic flagellate Trichomonas vaginalis and its homologue from Trichomonas gallinae do not belong to this family of proteins. Also, phylogenetic analysis of genes encoding mitochondrial-type chaperonin 60 proteins (HSP 60) supports the conclusion that the hydrogenosomes of anaerobic chytrids and anaerobic ciliates had independent origins, although both of them arose from mitochondria

A hydrogenosomal [Fe]-hydrogenase from the anaerobic chytrid Neocallimastix sp. L2

The presence of a [Fe]-hydrogenase in the hydrogenosomes of the anaerobic chytridiomycete fungus Neocallimastix sp. L2 has been demonstrated by immunocytochemistry, subcellular fractionation, Western-blotting and measurements of hydrogenase activity in the presence of various concentrations of carbon monoxide (CO). Since the hydrogenosomal hydrogenase activity can be inhibited nearly completely by low concentrations of CO, it is likely that the [Fe]-hydrogenase is responsible for at least 90% of the hydrogen production in isolated hydrogenosomes. Most likely, this hydrogenase is encoded by the gene hydL2 that exhibits all the motifs that are characteristic of [Fe]-hydrogenases. The open reading frame starts with an N-terminal extension of 38 amino acids that has the potential to function as a hydrogenosomal targeting signal. The downstream sequences encode an enzyme of a calculated molecular mass of 66.4 kDa that perfectly matches the molecular mass of the mature hydrogenase in the hydrogenosome. Phylogenetic analysis revealed that the hydrogenase of Neocallimastix sp. L2. clusters together with similar (‘long-type’) [Fe]-hydrogenases from Trichomonas vaginalis, Nyctotherus ovalis, Desulfovibrio vulgaris and Thermotoga maritima. Phylogenetic analysis based on the H-cluster – the only module of [Fe]-hydrogenases that is shared by all types of [Fe]-hydrogenases and hydrogenase-like proteins – revealed a monophyly of all hydrogenase-like proteins of the aerobic eukaryotes. Our analysis suggests that the evolution of the various [Fe]-hydrogenases and hydrogenase-like proteins occurred by a differential loss of Fe–S clusters in the N-terminal part of the [Fe]-hydrogenase.

Hydrogenosomes: convergent adaptations of mitochondria to anaerobic environments

Hydrogenosomes are membrane-bound organelles that compartmentalise the Final steps of energy metabo I is in in a number of anaerobic eukaryotes. They produce hydrogen and ATP. Here we will review the data, which are relevant for the questions: how did the hydrogenosomes originate, and what was their ancestor? Notably, there is strong evidence that hydrogenosomes evolved several times as adaptations to anaerobic environments. Most likely, hydrogenosomes and mitochondria share a common ancestor, but an unequivocal proof for this hypothesis is difficult because hydrogenosomes lack an organelle genome - with one remarkable exception (Nyctoherus ovalis). In particular, the diversity of extant hydrogenosomes hampers a straightforward analysis of their origins. Nevertheless, it is conceivable to postulate that the common ancestor of mitochondria and hydrogenosomes was a facultative anaerobic organelle that participated in the early radiation of unicellular eukaryotes. Consequently, it is reasonable to assume that both, hydrogenosomes and mitochondria are evolutionary adaptations to anaerobic or aerobic environments, respectively

Biodiversity of rumen ciliates

International audienceThe rumen, a specialized foregut in herbivorous animals (Ruminantia), hosts microbiota of archaea, eubacteria, anaerobic fungi, and ciliated protozoa. Microscopic observations re-veal that the endosymbiotic ciliates account for about 50% of the total microbial mass in the rumen: up to 100 billions of ciliates may populate the rumen of a single cow. These ciliates play an important role in fibre digestion and the modulation of the fermentation pro-files. Classical (morphological) studies have identified more than 250 species of ciliates living in the various ruminants1,2. The number of species in an individual host is known to be highly variable, but the average number of species has been reported about 20 in cat-tle3, but less in sheep3 and goats4. However, as in all protists, the limited number of distinct morphological traits hampers an assessment of the ciliate diversity in the rumen. Molecular studies on rumen ciliates are rare, mainly due to difficulties in culturing these ciliates in vi-tro. Here we describe a molecular approach to study the phylogenetic diversity of rumen protozoa. The diversity of rumen protozoa was analysed by sequencing of 18S rDNA li-braries that have been created from PCR-amplified DNA of total rumen contents of cow, sheep, and a goat. These sequences were compared with the sequences of rumen ciliates obtained from GenBank and ERCULE. The phylogenetic analysis suggests that the ciliate population of the ruminal ecosystem can be much more diverse than previously assumed

Diversity of rumen ciliates from domestic and wild animals

International audienceHere we describe the first molecular approach to study the diversity of rumen protozoa of wild animals. Total DNA was extracted from the rumen content of the red deer (Cervus elaphus) and the 18S rRNA genes were amplified by PCR. A library of ciliate 18S rRNA genes was created and a sample of 35 clones were sequenced partially. With the aid of the sequences of validated rumen ciliate representatives from the culture collection obtained in the frame of the ERCULE project (www.ercule.com) and those deposited in the EMBL gene databank, we were able to identify the phylogenetic position of the ciliates found in the rumen of a single red deer. Notably, none was identical to a previously analysed 18S rDNA sequence and many of the sequences were quite different from those known from the 364 sequences recovered from an analysis of the ciliate communities in cow sheep and goat. Interestingly, several of the clones recovered from the red deer clustered with Polyplastron, a genus that hasn't been reported for these animals until now (1)

The competitive success of Methanomicrococcus blatticola, a dominant methylotrophic methanogen in the cockroach hindgut, is supported by high substrate affinities and favorable thermodynamics

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Polyubiquitin genes in rumen ciliates : Domain shuffling and codon tolerance

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The energy metabolism of Methanomicrococcus blatticola: physiological and biochemical aspects

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