No description available.

Thesis (Ph.D.)--University of Delaware, 2006. / Principal faculty advisor: George W. Luther, III., College of Marine and Earth Studies. Includes bibliographical references.

Thesis (Ph. D.)--University of Washington, 2003. / Vita. Includes bibliographical references (p. 136-156).

The ability of micro–algae to respond to diverse and often rapidly changing habitats has been attributed to the versatility of their cellular lipids. Amongst these the energy rich triacylglycerols (TAG) have attracted considerable attention due to their potential use as feedstock for renewable biofuel. Although micro-algae have considerable advantages over other biofuel sources there are constraints to their utilisation. Improvements are required in certain areas including efficiencies in production and enhanced lipid yields if micro-algal biofuels are to become commercially feasible. To achieve this, genetic and metabolic manipulation will be essential and therefore a greater understanding of the lipid biosynthetic pathways is required. In this study the expression of genes putatively involved in TAG biosynthesis in the diatom Phaeodactylum tricornutum was investigated, for the first time, with CO2 supplementation and low pH stress over the entire growth cycle. This molecular analysis was combined with physiochemical examination of the lipid accumulation in the micro-algal model. The results indicated that TAG accumulation was enhanced by CO2 supplementation and occurred predominantly during the stationary growth phase. The molecular analysis revealed increased expression for three genes of interest, encoding enzymes involved in the acyl dependent pathway: Glycerol-3-phosphate acyl transferase (GPAT) -7198728 (Phatrdraft_50031), lysophosphatidic acyl transferase (LPAAT) -7196550 (Phatrdraft_42446) and phosphotidic acid phosphatase (PAP) -7195747 (Phatrdraft_40261) in cultures supplemented with CO2. Under the same conditions up-regulation of a gene involved in the first committed step of fatty acid biosynthesis, Acetyl CoA carboxylase (ACC) -7194806 (Phatrdraft_54926) was also observed. Overall, this study provides further insight on the specific genes linked with increased TAG production in P. tricornutum and the identification of references genes suitable for normalisation of qPCR data across the growth cycle and under CO2 supplementation, thus providing the tools needed for future molecular studies of P. tricornutum lipid production.

A series of studies were conducted to ascertain the importance of autotrophic picoplankton (0.2 - 2.0 fm in the longest dimension) in freshwaters. These included surveys of populations in lakes and rivers, and experiments on strains which had been isolated in clonal, axenic culture. Methods were developed to preserve, count and identify autotrophic picoplankton. Epifluorescence microscopy was used routinely throughout the study and it was shown that cells could be preserved in buffered formalin or glutaraldehyde for at least 12 months without a loss in cell count. Autotrophic picoplankton fluoresced red or orange depending on the photosynthetic pigments present, and a method based on fluorescence characteristics was developed to distinguish cyanobacterial from eukaryotic cells. Eukaryotes fluoresced most intensely under blue excitation light and were barely visible under green excitation light and cyanobacterial cells had the reverse response. In addition, fluorescence from eukaryotic cells faded faster than the fluorescence from cyanobacterial cells. Samples from standing waters from around the world were collected from 5 continents in a survey to discover how widespread autotrophic picoplankton are in the world; densities ranged from 1.02 x 10(^6) from a pool in Saudi Arabia to 1.20 x 10(^6) in Ennerdale Water in the UK. A survey of 30 lakes in northern England and Scotland revealed autotrophic picoplankton in every sample. Cell densities ranged from a minimum of 1.02 x 10(^2) in Esthwaite Water to a maximum of 4.26 x 10(^5) in Ennerdale Water. In two mountain streams the only autotrophic picoplankton found were aberrant. Studies on the seasonality of autotrophic picoplankton from 10 UK lakes showed that population densities differed by at least two orders of magnitude in a year. In every lake densities reached a maximum at mid- to late summer and highest densities were found in nutrient-poor waters. There was a marked difference in the relative abundance of orange and red fluorescing cells in all lakes. A number of standard methods were used to isolate and purify strains of autotrophic picoplankton, including a novel method using a laser flow cytometer to purify bacterized unialgal cultures. 14 strains were studied (9 obtained the author) and they demonstrated different growth rates when grown with different nitrogen substrates and when grown under different photon flux density. Twelve strains showed cell-bound phosphomonoesterase activity at pH 10.3 and nine strains showed cell bound phosphodiesterase activity at pH 10.3. No strain showed evidence of nitrogen fixation, chemoheterotrophic growth, desiccation tolerance, motility nor chromatic adaptation.

The algae in one soil sample from a rice-field in the southern marshes of Iraq were studied in detail. 11 taxa were found by direct microscopic inspection, with Microcoleus chthonoplastes and Nostoc muscorum the dominants. A total of 49 taxa were noted after various enrichment culture techniques. The influence of temperature, light, salinity, reducing conditions, nitrogen sources and phosphorus (phosphate) were tested on mixed populations. Blue-green algae dominated all cultures incubated at temperatures between 25-45 C, while eukaryotic algae dominated cultures at lower temperatures (10-20 C). Six taxa showed good growth in a medium enriched with 0.5 M NaC1and three also grew at 1 M NaC1, though growth was very slow. Most of heterocystous blue-green algae were sensitive to reducing conditions (0.1 mM Na(_2)S). As a consequence, in mixed populations there was an increase in the relative abundance of non-heterocystous forms. Fifteen strains were brought into clonal culture, nine of them also being axenics Anabaena cylindrica, three Calothrix spp., Cylindrospermum muscicola, Gloeotrichia sp., Hapalosiphon welwitschii, Microcoleus chthonoplastes, Nostoc muscorum. Detailed morphological and physiological studies were made for 14 strains under different nitrogen and phosphorus conditions. All asenic cultures showed marked alkaline phosphatase activity under phosphorus-deficient conditions. They were capable of utilizing a wide range of organic phosphorus compounds as a sole source of phosphorus. Axenic cultures of heterocystous strains were capable of fixing nitrogen, judged by positive results obtained with acetylene reduction assays. Nitrogen fixation and heterocyst differentiation of these strains was almost completely suppressed when the strains were grown with high concentrations of combined nitrogen (initial = 140 mg 1(^-1)NO(_3)-N or 50 mg l (^-1) NH(_4)-N).A discussion is included of how field research on these algae might indicate ways of modifying cultivation practices to increase the phosphorus and nitrogen status of the soil and also how algal morphology might be used to help indicate the nutrient status of the soil.

The morphology and nitrogenase activity (ARA) of Gloeotrichia pisum Thur. growing on deepwater rice were studied in situ at Sonargaon, Bangladesh, and compared with results from laboratory studies. The alga showed obvious similarities and dissimilarities. Hairs, gas vacuoles and akinetes, which were found in the field, were not found In the laboratory, even though the influences of quantity and quality of light flux and nutrient deficiency were tested. The response of nitrogenase to changes in light flux was rapid. A reduction in flux brought about similar results in the field and In the laboratory. Diel changes in nitrogenaee activity showed a maximum at mid-day In the presence of maximum light flux, but considerable activity (3.7% of dally total) took place at night. The activity In a medium free of combined carbon by bacteria free G. pisum indicates that the rate and duration of nitrogenase activity in the dark depend on the preceding light conditions. In batch culture, higher nitrogenase activity was observed when dark-grown alga was reilluminated, than the maximum activity ever found under continuous Illumination. The variation of nitrogenase activity in batch culture was studied in relation to the growth characteristics and developmental stages of the alga. Maximum activity (1.4 nmol C(_2)H(_4) µg ch1 a(^-1) min(^-1)), was observed after about one day of growth under continuous light. During this period, juvenile filaments were abundant (hence maximum heterocyst frequency), cyanophycin granules lacking and cultures had the lowest ch1 a : d. wt ratio. Heterocyst differentiation occurred between 14 and 24 h of growth and cell division was observed only after heterocyst differentiation. It appears that the juvenile filament is the most active nitrogen fixer during the life cycle of the alga. Reasons for low nitrogenase activity of about 0.352 nmol C(_2)H(_4) µg ch1 a(^-1) min (^-1) in the field have been discussed. It is estimated from diel changes in N(_2)-fixing activity and based on ARA of 77.4 nmol C(_2)H(_4) tiller(^-) min(^-1) and(^2) using some approximations, that G. pisum contributed about 4 kg N ha(^-1) season" in deepwater rice fields at Sonargaon in 1983.A brief morphological study was also Included. In the field, rapid colonization was observed on freshly submerged rice culms. Colonies contained Intersheath spaces on their periphery and exhibited zonation of filaments. In the larger ones. The mechanism of the formation of a radiating colony in the laboratory has been described and discussed. Differentiation of a hormogonium into a filament was studied in batch culture. The basal youngest cell differentiated into a heterocyst, whilst the rest of cells divided repeatedly, forming several groups of cells in a row. Subsequently most of these groups of cells were liberated successively as hormogonia.

No description available.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 123-136). Also available via the Internet.

Thesis (M.S.) in Ecology and Environmental Science--University of Maine, 2008. / Includes vita. Includes bibliographical references (leaves 51-56).