Multiple acquisition of methanogenic archaeal symbionts by anaerobic ciliates.

Anaerobic heterotrichous ciliates (Armophoridae and Clevelandellidae) possess hydrogenosomes that generate molecular hydrogen and ATP. This intracellular source of hydrogen provides the basis for a stable endosymbiotic association with methanogenic archaea. We analyzed the SSU rRNA genes of 18 heterotrichous anaerobic ciliates and their methanogenic endosymbionts in order to unravel the evolution of this mutualistic association. Here, we show that the anaerobic heterotrichous ciliates constitute at least three evolutionary lines. One group consists predominantly of gut-dwelling ciliates, and two to three, potentially four, additional clades comprise ciliates that thrive in freshwater sediments. Their methanogenic endosymbionts belong to only two different taxa that are closely related to free-living methanogenic archaea from the particular ecological niches. The close phylogenetic relationships between the endosymbionts and free-living methanogenic archaea argue for multiple acquisitions from environmental sources, notwithstanding the strictly vertical transmission of the endosymbionts. Since phylogenetic analysis of the small-subunit (SSU) rRNA genes of the hydrogenosomes of these ciliates indicates a descent from the mitochondria of aerobic ciliates, it is likely that anaerobic heterotrichous ciliates hosted endosymbiotic methanogens prior to their radiation. Therefore, our data strongly suggest multiple acquisitions and replacements of endosymbiotic methanogenic archaea during their host's adaptation to the various ecological niches.

Biocompatibility evaluation of sol-gel coatings for subcutaneously implantable glucose sensors.

The objective of the current investigation is to determine the soft-tissue biocompatibility of sol-gel matrices which can be used to optimize the properties of implantable glucose sensors. The biocompatibility of sol-gel matrices with heparin, dextran sulphate, Nafion, polyethylene glycol, and polystyrene sulphonate was examined in vitro in simulated body fluid and with cell culture experiments using human dermal fibroblasts. Finally, an in vivo study was performed. Therefore, sol-gel coated polystyrene discs were inserted subcutaneously in the back of rabbits. After 4 and 12 weeks, the implants with surrounding tissue were retrieved and processed histologically. In simulated body fluid, the formation of a granular calcium phosphate precipitate was observed. Cell proliferation on polyethylene glycol, Nafion, and heparin coated substrates was comparable to control samples and significantly higher than on dextran sulphate and polystyrene sulphate coated substrates. Light microscopic evaluation of the retrieved in vivo samples showed a fair tissue reaction to all materials. Histomorphometric analysis demonstrated that there were no differences in tissue response to the different sol-gel coatings. In conclusion, sol-gel matrices exhibit a fair biocompatibility both in vitro and in vivo. These results will form the basis for further research into the real merits of sol-gel coatings in optimizing the properties of subcutaneously implantable glucose sensors.

Voltage-dependent reversal of anodic galvanotaxis in Nyctotherus ovalis.

Aerobic and anaerobic ciliates swim towards the cathode when they are exposed to a constant DC field. Nyctotherus ovalis from the intestinal tract of cockroaches exhibits a different galvanotactic response: at low strength of the DC field the ciliates orient towards the anode whereas DC fields above 2-4 V/cm cause cathodic swimming. This reversal of the galvanotactic response is not due to backward swimming. Rather the ciliates turn around and orient to the cathode with their anterior pole. Exposure to various cations, chelators, and Ca(2+)-channel inhibitors suggests that Ca(2+)-channels similar to the "long lasting" Ca(2+)-channels of vertebrates are involved in the voltage-dependent anodic galvanotaxis. Evidence is presented that host-dependent epigenetic factors can influence the voltage-threshold for the switch from anodic to cathodic swimming.

Evolution of anaerobic ciliates from the gastrointestinal tract: phylogenetic analysis of the ribosomal repeat from Nyctotherus ovalis and its relatives.

The 18S and 5.8S rDNA genes and the internal transcribed spacers ITS-1 and ITS-2 of ciliates living in the hindgut of frogs, millipedes, and cockroaches were analyzed in order to study the evolution of intestinal protists. All ciliates studied here belong to the genus Nycrotherus. Phylogenetic analysis revealed that these ciliates from a monophyletic group that includes the distantly related anaerobic free-living heterotrichous ciliates Metopus palaeformis and Metopus contortus. The intestinal ciliates from the different vertebrate and invertebrate hosts are clearly divergent at the level of their rDNA repeats. This argues for the antiquity of the associations and a predominantly vertical transmission. This mode of transmission seems to be controlled primarily by the behavior of the host. The different degrees of divergence between ciliates living in different strains of one and the same cockroach species most likely reflect the different geographical origins of the hosts. In addition, host switches must have occurred during the evolution of cockroaches, since identical ciliates were found only in distantly related hosts. These phenomena prevent the reconstruction of potential cospeciation events.