Chlorella-bearing ciliates dominate in an oligotrophic North Patagonian lake (Lake Pirehueico, Chile): abundance, biomass and symbiotic photosynthesis

1. Large mixotrophic ciliates ( Stentor araucanus , S. amethystinus and Ophrydium naumanni ) were a characteristic component of a temperate, oligotrophic lake in North Patagonia. During a 1-year study, the abundance, biomass and primary production of these large Chlorella -bearing ciliates were compared with those of the total plankton community.
2. Mixotrophic ciliates peaked in spring and from late summer to autumn, accounting for 1.6–43% (annual average: 16.3%) and 67–99% (annual average: 92%) of total ciliate abundance and biomass, respectively. Their contribution to total zooplankton biomass, including flagellates, rotifers, ciliates and crustaceans, was 14–76%, or 47% as an annual average. Endosymbiotic algae accounted for up to 25% of total autotrophic biomass (annual mean: 3.9%).
3. Maximum cell-specific photosynthetic rates of S. araucanus and S. amethystinus at light saturation varied between 80 and 4400 pg C ciliate^–1 h^–1 with high values during autumn and winter, and low values during summer. The depth-integrated rates of photosynthesis (0–40 m) of algal endosymbionts contributed 1–25% to total photosynthesis (annual mean: 6.5%).
4. A comparison of calculated ingestion rates with photosynthetic rates of Stentor indicates that photosynthate produced by endosymbionts generally exceeded heterotrophic food supply of Stentor during autumn and winter, but was much lower during summer, when food supply was high.
5. The mixotrophic ciliates represent an important 'link' between nanoplankton and higher trophic levels within the plankton community because of their high heterotrophic biomass and considerable contribution to total photosynthesis.     

Ecology of cavernicolous ciliates from the anchihaline lagoons of Mallorca

On the island of Mallorca, anchihaline lagoons, meromictic in character, are common in the flooded coastal karst. These subterranean lagoons, containing important populations of crustacea, maintain a connection, albeit tenuous, to the sea. Thus, the first truly quantitative study of marine ciliates inhabiting anchihaline lagoons was undertaken between April 1996 and April 1997. Physical and chemical measurements were taken in-situ, together with water samples for faunal analysis in each of four stratified lakes. These lagoons typically displayed a temperature inversion, an increase in conductivity and a decrease in dissolved oxygen concentration with depth. Ciliates were present in all lagoons studied, with a total of nine species recorded. All were assigned to known taxa. Spatial distribution of the trophic cells was noteworthy with populations clearly stratified within the water column, most being found at the waters surface, sometimes in association with rafts of floating calcite crystals, or in the sediment. Only on one occasion were ciliates recorded in mid-water. Abundance was very low, typically <1 ciliate cm^–3. The floating calcite crystals may form a delimitable biotope for ciliate populations. The role of the cyst in maintaining populations of ciliates in these cave waters is discussed.     

Description of the Infraciliature and Morphogenesis in the Ciliate Urotricha ondina N. Sp. (Prorodontida, Urotrichidae)

Recent works on prostomatid ciliates show that some genera of this group have a differentiated oral infraciliature and that their stomatogenesis during division involves the proliferation of only a few somatic kineties. These findings have significant implications regarding the iaxonomic status of these genera and also on the terminology used for the oral structures. In Urotricha ondina , the oral infraciliature consists of (1) a paroral kinety formed of paired kinetosomes that encircle the cytostome at the anterior pole of the cell and (2) 3 adoral organelles, each formed of 2 rows of kinetosomes, ventral in position and obliquely disposed, lying above 3 short somatic kineties that do not reach the anterior pole of the cell. This oral ciliature —formerly known as the corona and brosse, respectively—originate during stomatogenesis from the proliferation of 4 somatic kineties that lie posterior to the adoral organelles of the parental cell.     

The Cultivation of Symbiote-free Marine Ciliates in Axenic Medium

SYNOPSIS. Media have been developed for axenic cultivation of 10 strains belonging to 7 species of small marine ciliates. A medium containing cerophyl extract, proteose peptone, trypticase, yeast nucleic acid, biotin, calcium pantothenate folic acid, nicotinamide, pyridoxal HCl, riboflavin, thiamine HCl, and DL-thioctic acid in sea water supports the growth of Uronema nigricans strains Pc and 34/2, Parauronema virginiatum strains 2/1 and 19/1, Miamiensis avidus strains Ma and 19/3, Miamiensis sp. strain 1/1, a strain of "G" ciliate, and strains 33/8 and 34/7 of 2 unidentified species. By substituting a mixture of asolecithin, cephalin, and Tween 80 for cerophyl in the medium, luxurious growth of all except the strains of the 2 unidentified species can be obtained. A defined medium consisting of 18 amino acids, 5 purine derivatives, 8 vitamins, asolecithin, cephalin, and Tween 80 in synthetic sea water also has been developed for 6 of the strains: M. avidus Ma and 19/3, Miamiensis sp. 1/1, P. virginiatum 2/1 and 19/1, and U. nigricans Pc. In general the ciliates grow best at pH 7.2 in the dark at 27 C in media containing sea water of density = 1.015. Under these conditions maximum populations are reached in 4–5 days and range from several hundred thousand to 3 or 4 × 10⁶ depending upon the strain. Electronmicroscopic observations for the presence of endosymbiotes gave negative results.     

Nonstandard genetic codes and translation termination

Genetic code is not universal. Various nonstandard versions of the code are known for some mitochondrial, prokaryotic, and eukaryotic genomes. The most common deviation is stop codon reassignment; i.e., a stop codon is decoded as a sense codon rather than as a signal for translation termination. Class 1 release factors (RFs: prokaryotic RF1 and RF2 and eukaryotic eRF1) recognize the stop codons and induce hydrolysis of peptidyl-tRNA in the ribosome. The specificity of class 1 RFs changes in organisms with a nonstandard code. The rare amino acids selenocysteine and pyrrolysine utilize essentially different decoding strategies. The review considers several hypotheses of the origin of nonstandard genetic codes. A new hypothesis is advanced, assuming a change in the specificity of class 1 RFs as a starting point for stop codon reassignment.     

Variation in macronuclear genome content of three ciliates with extensive chromosomal fragmentation: a preliminary analysis

The genome architecture of ciliates, including features such as nuclear dualism and large-scale genome rearrangements, impacts gene and genome evolution in these organisms. To better understand the structure of macronuclear chromosomes in ciliates with extensively processed chromosomes, a sample of complete macronuclear chromosomes was sequenced from three ciliate species: Metopus es (Class [Cl]: Armophorea), Nyctotherus ovalis (Cl: Armophorea), and Chilodonella uncinata (Cl: Phyllopharyngea). By cloning whole macronuclear chromosomes into a plasmid vector, we generated nine clones from each of M. es and C. uncinata, and 37 clones from N. ovalis. Analysis of these macronuclear chromosomes provides insight into the evolution of genome features such as chromosome content, gene structure, and genetic code. Phylogenetic patterns can be found in telomere structure and codon usage, which are both more similar in M. es and N. ovalis than C. uncinata. In addition, we provide evidence of lateral transfer of a bacterial endo-beta-mannanase gene onto a M. es chromosome and report the discovery of a 42-bp conserved sequence motif within N. ovalis untranslated regions.     

The biodiversity and ecology of Antarctic lakes: models for evolution

Antarctic lakes are characterised by simplified, truncated food webs. The lakes range from freshwater to hypersaline with a continuum of physical and chemical conditions that offer a natural laboratory in which to study evolution. Molecular studies on Antarctic lake communities are still in their infancy, but there is clear evidence from some taxonomic groups, for example the Cyanobacteria, that there is endemicity. Moreover, many of the bacteria have considerable potential as sources of novel biochemicals such as low temperature enzymes and anti-freeze proteins. Among the eukaryotic organisms survival strategies have evolved, among which dependence on mixotrophy in phytoflagellates and some ciliates is common. There is also some evidence of evolution of new species of flagellate in the marine derived saline lakes of the Vestfold Hills. Recent work on viruses in polar lakes demonstrates high abundance and high rates of infection, implying that they may play an important role in genetic exchange in these extreme environments.     

A proteomics approach to cloning fenestrin from the nuclear exchange junction of tetrahymena

ABSTRACT. We set out to find the " fenestrin " gene, a gene whose protein is associated with numerous cellular apertures, including the nuclear exchange junction in mating Tetrahymena thermophila . First we developed protocols for imaging and isolating intact nuclear exchange junctions from conjugating cells. Proteins from these junctions were purified using SDS-PAGE, subjected to limited proteolysis, and precise molecular weights were determined by mass spectrometry. Using Protein Prospector^® software and the published Tetrahymena Genome Database, genes for 15 of the most abundant proteins found in our extracts were identified. The most promising candidate was cloned by PCR, fused to yellow fluorescent protein (YFP), and placed under the control of an inducible metallothionein promoter. YFP-localization within live Tetrahymena transformants strongly suggested that one of these genes encoded the fenestrin protein, a result that was subsequently confirmed by Western blotting.