The [FeFe] hydrogenase of Nyctotherus ovalis has a chimeric origin

BACKGROUND: The hydrogenosomes of the anaerobic ciliate Nyctotherus ovalis show how mitochondria can evolve into hydrogenosomes because they possess a mitochondrial genome and parts of an electron-transport chain on the one hand, and a hydrogenase on the other hand. The hydrogenase permits direct reoxidation of NADH because it consists of a [FeFe] hydrogenase module that is fused to two modules, which are homologous to the 24 kDa and the 51 kDa subunits of a mitochondrial complex I. RESULTS: The [FeFe] hydrogenase belongs to a clade of hydrogenases that are different from well-known eukaryotic hydrogenases. The 24 kDa and the 51 kDa modules are most closely related to homologous modules that function in bacterial [NiFe] hydrogenases. Paralogous, mitochondrial 24 kDa and 51 kDa modules function in the mitochondrial complex I in N. ovalis. The different hydrogenase modules have been fused to form a polyprotein that is targeted into the hydrogenosome. CONCLUSION: The hydrogenase and their associated modules have most likely been acquired by independent lateral gene transfer from different sources. This scenario for a concerted lateral gene transfer is in agreement with the evolution of the hydrogenosome from a genuine ciliate mitochondrion by evolutionary tinkering

Diversity and Abundance of Bolidophyceae (Heterokonta) in Two Oceanic Regions

The diversity and abundance of the Bolidophyceae (Heterokonta), a newly described picoplanktonic algal class which is a sister group to the diatoms, was assessed in the equatorial Pacific Ocean and in the Mediterranean Sea by culture isolation, molecular biology techniques, and pigment analyses. Eight strains of Bolidophyceae were isolated in culture from different mesotrophic and oligotrophic areas. The corresponding small subunit (SSU) rRNA gene sequences allowed us to design two probes specific for the Bolidophyceae. These probes have been used in natural samples (i) to selectively amplify and detect Bolidophyceae sequences and (ii) to quantify the relative abundance of Bolidophyceae within the picoeukaryote community. Sequences available to date indicate that the class Bolidophyceae comprises at least three different clades, two corresponding to the previously described species Bolidomonas pacifica and Bolidomonas mediterranea and the third one corresponding to a subspecies of B. pacifica. Amplification of the SSU rRNA gene from natural samples with universal primers and hybridization using a Bolidomonas-specific probe followed by a eukaryote-specific probe allowed us to estimate the contribution of the Bolidophyceae to the eukaryotic DNA in both Pacific and Mediterranean waters to be lower than 1%. Similarly, high-performance liquid chromatography analyses of fucoxanthin, the major carotenoid present in Bolidophyceae, indicated that less than 4% of the total chlorophyll a in the picoplanktonic fraction in the equatorial Pacific was due to Bolidophyceae. Consequently, although strains of Bolidophyceae have been isolated from samples collected at several stations, this new class seems to have been a minor component of the natural picoeukaryotic populations in the ecosystems investigated, at least during the periods sampled

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)

Rapid indentification of rumen protozoa by restriction analysis of amplified 18S rRNA gene

A rapid method has been developed for molecular identification of rumen ciliates without the need for cultivation. Total DNA was isolated from single protozoal cells by the Chelex method and nearly complete protozoal 18S rRNA genes were amplified and subjected to restriction fragment length polymorphism analysis. On the basis of restriction patterns generated a molecular key was elaborated allowing identification of protozoa solely by a molecular technique without prior knowledge of morphology. No differences were observed between identical species originating from different animals or geographic locations, or between morphological variants of the same species. The ARDREA analysis described here provides a rapid and convenient way for identification and diversity studies of rumen protozoa