Cilia and flagella are sensory organelles, found in the majority of eukaryotic organisms that play a vital role in the general physiology, health and early development of humans. Intraflagellar transport (IFT) is tasked with building and maintaining the entire ciliary structure by facilitating the transport of axonemal precursors, trafficking of ciliary membrane proteins and turnover products. Currently, there are no complete models detailing how ciliated organisms regulate the entry and exit of IFT particles, a multi-meric adaptor complex that ferries flagellar proteins. In this thesis, I focus on small Rab-like protein IFT22, an IFT-particle integrated protein with predicted GTPase activity, as a potential regulatory component of IFT particle trafficking in Chlamydomonas. Using an artificial microRNAs strategy, I show that IFT22 regulates the available cellular pool of IFT particles and the distribution profile of the IFT particles between the cytoplasm and the flagellar compartment. Additionally, I demonstrate how the putative constitutive active mutant of IFT22 is able properly localize to the peri-basal body and enter the flagellar compartment using immunofluorescence and immunoblot analysis of flagella extracts. Finally, preliminary RNAi data suggests IFT25 the IFT particle/motor/BBSome assembly downstream of IFT22 regulation, evident from the depletion of kinesin-2 subunit FLA10, IFT-dynein-2 subunit D1bLIC and BBsome component BBS3from whole cell extracts of IFT25 knockdown transformants.

Le cytochrome b6f est un complexe majeur de la chaîne photosynthétique oxygénique de par son activité quinol:plastocyanine oxydoréductase, qui contribue à la formation d'ATP via un transfert d'électrons couplé à un transfert de protons. La présence d'un hème c particulier lié par une seule liaison covalente, l'hème ci, au sein du site de réduction de quinone Qi du cytochrome b6f constitue une différence notable en comparaison avec son homologue de la chaîne respiratoire, le cytochrome bc1. Un cytochrome b6f dépourvu d'hème ci est dégradé, sa faible accumulation ne permet pas une croissance photosynthétique. Cette observation a donné lieu à une recherche de suppresseurs permettant une plus grande accumulation de cytochrome b6f dont la fonction même altérée, serait suffisante pour assurer une croissance photosynthétique. Cette approche génétique de recherche de suppresseur a été entreprise chez Chlamydomonas reinhardtii. Ce travail de thèse a permis l'isolation et la caractérisation d'un mutant de la protéase FtsH1 (mutation R420C qui affecterait l'activité ATPasique). Le mutant ftsh1-1 s'est révélé être un outil puissant pour l'étude fonctionnelle de complexes mutés autrement dégradés. Une approche multidisciplinaire combinant expériences de génétique, biochimie, physiologie et biophysique a démontré notamment que : (i) le mutant QiKO, dont le complexe b6f est dépourvu des hèmes bh et ci, peut pousser de manière phototrophique malgré un Q-cycle cassé, (ii) l'absence d'hème ci lié covalemment, pour le mutant Rccb2, génère une photosensibilité exacerbée en présence d'oxygène, ce qui sous-tend un rôle pour l'hème ci dans un environnement riche en oxygène, (iii) la protéase FtsH exerce un contrôle qualité global des complexes majeurs photosynthétiques.

The primary aim of the research summarized in this thesis was to confirm or refute that algae are involved in metal sedimentation from surface water, and whether this activity, if any, is enhanced by increased phosphorus availability. <p>A small-scale laboratory-based experiment was devised to elucidate the role of the chlorophyte alga Chlamydomonas noctigama in the removal of arsenic, nickel and uranium from mine water. Results indicated that the presence of <i>C. noctigama</i> significantly enhanced the removal of these metals relative to treatments without cells. Metals were present in greater concentrations in particulate matter in treatments with cells compared to treatments without cells, and there was a corresponding decrease in the concentrations of dissolved metals. This leads to the conclusion that sedimentation was mainly biotically induced. <p>Additional evidence of biotic involvement in metal removal from water by <i>C. noctigama</i> was obtained by using EDX spectroscopy and X-PEEM spectromicroscopy to observe complexation of arsenic, nickel and uranium to C. noctigama cells. Arsenic, the metal which was present at the lowest concentration in the DJX water, was present on scanned cells in low concentrations, and nickel and uranium, which were present at high concentrations in the DJX water, were present at higher concentrations. Examination of a single cell using X-PEEM spectromicroscopy showed uranium co-localized with carbon and phosphorus on the exterior of the cell. Crystalline particulate matter may have increased in the presence of cells. EDX spectroscopy showed that the crystalline particulate matter was possibly hydroxyapatite that contained various metals, including arsenic, nickel and uranium. EDX spectroscopy was used to determine the frequencies at which the cell-metal and particulate matter-metal associations occurred, and the relative concentrations of the metals associated with particulate matter. <p>No correlation between metal removal and phosphorus concentration in the media, or between algal density and phosphorus concentration was observed. However, phosphorus concentrations were not growth-limiting in these experiments, and so the effect of phosphorus on abiotic precipitation of metals remains unclear. <p> Results suggest two mechanisms by which <i>C. noctigama</i> may remove arsenic, nickel and uranium from solution: by direct sorption to the exterior of the cell, and by sorption to a cell product. <p>An experiment using cells preserved in Lugols iodine (a common phytoplankton sample preservative) indiated that Lugols preserved samples could not be used to quantify metals using spectroscopy. Consequently, historical samples preserved with Lugols iodine cannot be analyzed by this method.

Thesis (Ph. D.)--University of Nevada, Reno, 1998. / Includes bibliographical references. Online version available on the World Wide Web.

No description available.

Environmental heterogeneity has often been suggested as a general explanation for patterns of diversity at scales ranging from individuals within populations to communities within landscapes. I evaluate this proposition using laboratory experiments with two microbial species, the unicellular chlorophyte Chlamydomonas reinhardtii and the common bacterium Pseudomonas fluorescens. These experiments contrast the fate of diversity following selection in heterogeneous and homogeneous environments. Specifically, I show that (1) an individual's breadth of adaptation evolves to match the amount of environmental variation, specialists evolving in environments that remain constant through time and generalists evolving in environments that vary through time irrespective of the scale at which environmental variation occurs relative to the lifetime of an individual; (2) the maintenance of diversity in a spatially heterogeneous environment is context-dependent, diversity being more readily maintained when environmental conditions are very different and genotypes are widely divergent; (3) selection in heterogeneous environments represents a plausible mechanism for two well-known patterns of diversity at large spatial scales, namely that between species diversity and both productivity and disturbance. This thesis thus demonstrates that environmental heterogeneity is a plausible, and perhaps very general, factor responsible for the diversity of natural communities.

Selenium (Se) is a micronutrient, yet elevated Se can be toxic to aquatic organisms. The range of Se concentrations within which Se uptake goes from insufficient to toxic is very narrow. It is thus important to understand the Se biogeochemical cycle in aquatic systems. In this thesis, the study focuses on changes in Se speciation during uptake by green algae. An optimized method was adopted to quantify and speciate Se in water using flow-injection atomic fluorescence spectroscopy coupled with high-pressure liquid chromatography. Details on the method are given here. For the uptake experiments, the uptakes of four Se species (selenite (Se-IV), selenate (Se-VI), selenocystine (Se-Cys) and selenomethionine (Se-Met)) by the green algae Chlamydomonas reinhardtii were compared. This thesis reports that the algae take up higher amounts of organic Se than inorganic Se. Selenomethionine (Se-Met) had the most rapid uptake, during which Se-Cys was produced. For all experiments, Se-IV was produced and found to sorb onto the algae cells, revealing that Se-IV is an important intermediate compound. Mass balance calculations revealed that more than 90% of Se was lost during uptake, probably to the atmosphere. This study also investigated the release of Se during algae decay to simulate the fate of Se during early-diagenesis. Selenium-rich algae cells were mixed with estuarine sediments at the sediment–water interface in a series of column incubations experiments. During the 7-week incubations, Se speciation was measured at the water–sediment interface and in pore water samples. We found that all the Se released to the pore water was in the form of Se-Cys. Although preliminary, these results highlight the key role of organic-Se species in the biogeochemical cycle of Se in the aquatic environment.

Thesis (Doctoral)--Universiteit van Amsterdam, 1982.

Techn. Universiẗat, Diss., 1999--Berlin.

Techn. University, Diss., 2003--Berlin.