Ecophysiology of mixotrophic flagellates

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ROTTBERGER, Julia, 2013. Ecophysiology of mixotrophic flagellates

@phdthesis{Rottberger2013Ecoph-27257, title={Ecophysiology of mixotrophic flagellates}, year={2013}, author={Rottberger, Julia}, address={Konstanz}, school={Universität Konstanz} }

Mixotrophy in algae is a type of nutrition situated between the metabolic modes of photoautotrophy (building biomass from inorganic molecules via photosynthesis) and chemoheterotrophy (building biomass from organic substances via uptake of food). Mixotrophic chrysophytes are a group of flagellate protists prospering during re-oligotrophication of Lake Constance. However, little is known about metabolic pathways of chrysophytes. The aim of this thesis was to investigate the physiological and molecular regulation of carbon metabolism in mixotrophic chrysophytes.<br /><br /><br /><br />As a first step comparative physiological analyses of nutritionally diverse chrysophytes were conducted. A particle analyser was shown to be a helpful tool to monitor chrysophyte cultures for bacterial contaminations, to perform cell counts and to detect changes in mean cell size, total cell biovolume and size distribution of the unicellular protists. Growth experiments under different light regimes and with different carbon sources demonstrated that Poteriospumella lacustris and the mixotrophic Poterioochromonas malhamensis could strive under chemoheterotrophic conditions. Both strains were not growing photoautotrophically, however, Poterioochromonas malhamensis showed some photosynthetic activity and was able to survive longer when kept in the light. Similar to the photoautotrophic diatom Phaeodactylum tricornutum, which served as a reference strain, the photoautototrophic strain Mallomonas annulata and the mixotrophic chrysophyte Dinobryon divergens showed light limited growth when kept in inorganic media. Even though Dinobryon divergens consumed living bacteria, it did not grow in the dark in the presence of bacteria. Due to the relevant differences in general nutritional preferences between the two mixotrophic strains Poterioochromonas malhamensis and Dinobryon divergens, we propose that during re-oligotrophication, Dinobryon divergens might primarily compete with photoautotrophic algae while Poterioochromonas malhamensis presumably mainly competes with chemoheterotrophic organisms and that they, thus, may colonize different vertical layers of the water column.<br /><br /><br /><br />In a second step Mallomonas annulata, Dinobryon divergens, Poterioochromonas malhamensis and Poteriospumella lacustris were grown under suitable culturing conditions according to the comparative physiological studies and transcriptomic analyses and comparisons were performed applying a 454-sequencing approach. A total of 213,361 contigs with an average length of 611 nucleotides were annotated and functionally sorted using BLAST2GO. The transcripts of the pathways of glycolysis, gluconeogenesis, Calvin Cycle, photorespiration and urea cycle were expressed in the photoautotrophic and both mixotrophic chrysophytes. Many metabolic parallels regarding primary carbon metabolism were found between Mallomonas annulata and the diatom Phaeodactylum tricornutum. However, the two mixotrophic strains differed from Mallomonas annulata by the absence of transcripts for putative key enzymes involved in the oxidative pentose phosphate pathway and carboxylating reactions localized in the plastid. These enzymes are important for photoautotrophic performance. A set of glycolytic transcripts of the heterotrophic chrysophyte was found to be targeted to the plastid targeted. This represents a first hint for metabolic activity in the colourless, non-photosynthetic plastid of Poteriospumella lacustris. Altogether this study lays a profound base for expression analyses of metabolic pathways of chrysophytes and further molecular studies. eng 2014-03-24T08:58:54Z deposit-license 2014-03-24T08:58:54Z 2013 Ecophysiology of mixotrophic flagellates Rottberger, Julia Rottberger, Julia

Dateiabrufe seit 01.10.2014 (Informationen über die Zugriffsstatistik)

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