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Exploring the diversity of snow algae using polyphasic approach
Procházková, Lenka ; Nedbalová, Linda (advisor) ; Karsten, Ulf (referee) ; Hoham, Ronald (referee)
Snow algae cause blooms in slowly melting snowfields in mountain and polar regions. Although they are excellent models for the study of life in extremely cold environments, their taxonomical diversity, geographical distribution and variety of physiological strategies used to cope with their harsh environment are only partially understood. This work was focused on green algae from the order Chlamydomonadales and in one case on golden algae from the order Hibberdiales. An integrative approach was applied to characterise species, including the sequencing of several molecular markers (18S rDNA, ITS2 rDNA, rbcL) to reveal genotypes and infer phylogenetic positions. Light and electron microscopy were conducted to describe the detailed structure of cell wall surfaces and intracellular compartments. Moreover, fatty acid and pigment profiling were carried out to provide new insights into the adjustments of metabolic pathways in these algae. Rapid light curve measurements were used as a proxy of light preferences of photosystem II. Firstly, one of the main algae responsible for causing the phenomenon of red snow was shown to represent a single, monophyletic lineage, independent from other algae within the Chlamydomonadales (paper I). Therefore, the new genus Sanguina (S.) was described, with two...
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Freezing tolerance of freshwater diatoms as a key to their success in polar regions
Hejduková, Eva ; Nedbalová, Linda (advisor) ; Karsten, Ulf (referee) ; Cantonati, Marco (referee)
II ABSTRACT (ENGLISH VERSION) Diatoms are microalgae characterised by a golden-brown colour and ornamented silica shells. They thrive in various environments worldwide ranging from aquatic marine and freshwater to terrestrial. Together with cyanobacteria and green algae, they are important primary producers in both polar regions (Arctic and Antarctica). The polar environment is characterised by extreme natural conditions, which microalgae have to overcome, such as low and freezing temperatures, desiccation, long periods of dark and irregular nutrient and liquid water availability. Many microorganisms overwhelmed by unfavourable conditions use dormancy and create stress resistant stages. Yet, freshwater pennate diatoms are not known to form such morphologically distinct stages. Despite this fact, they prosper well in many polar habitats. This doctoral thesis presents a summary of the challenges of life in polar environments and reviews the current knowledge of survival strategies of microalgae with the focus on freezing stress. The conducted research provides a deeper insight into survival of freshwater pennate diatoms in the severe conditions of the polar environment. Their tolerance to freezing stress was evaluated experimentally under laboratory conditions and by field observations over a one- year period...
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Exploring the diversity of snow algae using polyphasic approach
Procházková, Lenka ; Nedbalová, Linda (advisor) ; Karsten, Ulf (referee) ; Hoham, Ronald (referee)
Snow algae cause blooms in slowly melting snowfields in mountain and polar regions. Although they are excellent models for the study of life in extremely cold environments, their taxonomical diversity, geographical distribution and variety of physiological strategies used to cope with their harsh environment are only partially understood. This work was focused on green algae from the order Chlamydomonadales and in one case on golden algae from the order Hibberdiales. An integrative approach was applied to characterise species, including the sequencing of several molecular markers (18S rDNA, ITS2 rDNA, rbcL) to reveal genotypes and infer phylogenetic positions. Light and electron microscopy were conducted to describe the detailed structure of cell wall surfaces and intracellular compartments. Moreover, fatty acid and pigment profiling were carried out to provide new insights into the adjustments of metabolic pathways in these algae. Rapid light curve measurements were used as a proxy of light preferences of photosystem II. Firstly, one of the main algae responsible for causing the phenomenon of red snow was shown to represent a single, monophyletic lineage, independent from other algae within the Chlamydomonadales (paper I). Therefore, the new genus Sanguina (S.) was described, with two...
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Stress resistance of polar hydro-terrestrial algae Zygnema spp. (Zygnematophyceae, Streptophyta)
Pichrtová, Martina ; Němcová, Yvonne (advisor) ; Nedbalová, Linda (referee) ; Karsten, Ulf (referee)
Filamentous green microalgae of the genus Zygnema belong to the most common primary producers in the polar hydro-terrestrial environment. In such unstable habitats, organisms are subject to various stress factors, e.g., freeze-thaw cycles, desiccation and high irradiation levels. However, the stress resistance mechanisms that enable Zygnema spp. to thrive in this extreme environment are only partially understood. Therefore, polar Zygnema spp. were examined under various stress conditions using both field samples and cultures. Moreover, molecular phylogeny methods were applied that provided first insights into the diversity of polar Zygnema. Sequencing of the chloroplast gene rbcL revealed several different Zygnema genotypes and, surprisingly, one Zygnemopsis sp. with vegetative Zygnema sp. morphology. First set of experiments examined the effects of UV exposure. It turned out that polar strains of Zygnema produce phenolic substances as UV screens. These substances are most likely stored in vacuoles and other vesicles at the cell periphery, providing protection for other organelles. In the next study, Zygnema spp. were investigated under natural conditions in the Arctic. At the end of summer, the cells gradually lose their typical vegetative appearance (with large vacuoles and stellate chloroplasts)...
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