Browsing by Subject "Microalgae"
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Item Artificial Leaf for Biofuel Production and Harvesting: Transport Phenomena and Energy Conversion(2013-08) Murphy, Thomas Eugene; Berberoglu, HalilMicroalgae cultivation has received much research attention in recent decades due to its high photosynthetic productivity and ability to produce biofuel feedstocks as well as high value compounds for the health food, cosmetics, and agriculture markets. Microalgae are conventionally grown in open pond raceways or closed photobioreactors. Due to the high water contents of these cultivation systems, they require large energy inputs for pumping and mixing the dilute culture, as well as concentrating and dewatering the resultant biomass. The energy required to operate these systems is generally greater than the energy contained in the resultant biomass, which precludes their use in sustainable biofuel production. To address this challenge, we designed a novel photobioreactor inspired by higher plants. In this synthetic leaf system, a modified transpiration mechanism is used which delivers water and nutrients to photosynthetic cells that grow as a biofilm on a porous, wicking substrate. Nutrient medium flow through the reactor is driven by evaporation, thereby eliminating the need for a pump. This dissertation outlines the design, construction, operation, and modeling of such a synthetic leaf system for energy positive biofuel production. First, a scaled down synthetic leaf reactor was operated alongside a conventional stirred tank photobioreactor. It was demonstrated that the synthetic leaf system required only 4% the working water volume as the conventional reactor, and showed growth rates as high as four times that of the conventional reactor. However, inefficiencies in the synthetic leaf system were identified and attributed to light and nutrient limitation of growth in the biofilm. To address these issues, a modeling study was performed with the aim of balancing the fluxes of photons and nutrients in the synthetic leaf environment. The vascular nutrient medium transport system was also modeled, enabling calculation of nutrient delivery rates as a function of environmental parameters and material properties of the porous membrane. These models were validated using an experimental setup in which the nutrient delivery rate, growth rate, and photosynthetic yield were measured for single synthetic leaves. The synthetic leaf system was shown to be competitive with existing technologies in terms of biomass productivity, while requiring zero energy for nutrient and gas delivery to the microorganisms. Future studies should focus on utilizing the synthetic leaf system for passive harvesting of secreted products in addition to passive nutrient delivery.Item Detection, classification, genetic diversity and molecular evolution of algal viruses based on DNA polymerase genes(1995) Chen, Feng, 1964-; Suttle, Curtis Arnold, 1955-A polymerase chain reaction (PCR) technique with three highly degenerate primers (group-specific primers AVS1/AVS2 and nested primer POL) was developed to detect and amplify DNA polymerase genes (DNA pol) from 13 virus isolates which infect three genera of distantly related microalgae, Chlorella strains NC64A and Pbi, Micromonas pusilla and Chrysochromulina spp. Amplified DNA pol fragments were cloned and sequenced, and the genetic relatedness among algal viruses examined. Phylogenetic trees based on DNA pol sequences and hybridization of viral genomic DNA showed similar branching patterns. Genetic relatedness calculated from the hybridization and sequencing data showed a good concordance (r=0.90), indicating that DNA pol can be used to determine genetic relatedness and infer phylogenetic relationships among these viruses, and potentially among other organisms. It was found that nucleotide sequences of DNA pol share higher similarities among algal viruses than with other organisms, and viruses infecting the same species had higher sequence similarities than those infecting different species. Sequence analysis of inferred amino acid sequences of DNA pol from 24 double-stranded DNA viruses indicated that viruses which infect these microalgae form a distinct phyletic group, and are more closely related to herpes viruses than to other dsDNA viruses. The branching patterns of the phylogenetic tree corresponded well with groupings based on the International Committee on Taxonomy of Viruses. The study suggests that these algal viruses share a common ancestor and belong to the Phycodnaviridae. Nested PCR was also used to amplify DNA pol genes from natural virus communities concentrated by ultrafiltration and centrifugation, from the Gulf of Mexico. DNA pol genes from algal viruses were detected in 5 of 6 stations. The PCR products from an offshore station (station B11) were cloned, analyzed by restriction fragment length polymorphism (RFLP) and representative clones sequenced to examine the genetic diversity of algal viruses in nature. The five RFLP patterns or operational taxonomy units (OTUs) that were observed ranged from 9 to 34% of the 33 clones in the library. Based on sequence analysis four OTUs were closely related to the Micromonas viruses, whereas one OTU was an unknown algal virusItem The effect of 2E,4E-decadienal on lipid-related gene expression in Phaeodactylum tricornutum(2013-08) Beck, Emily Christine; Mehdy, Mona Cynthia, 1955-Microalgae have been proposed as a potential feedstock for biofuel production, and as a result, interest in the biology of these organisms has intensified. These organisms also synthesize lipids that are vital to human health and nutrition. Stress has been shown to have an effect on lipid composition and gene expression in microalgae, but many studies have focused on the effects of abiotic stressors. The purpose of this study was to investigate the effect of biotic stress on lipid-related gene expression in Phaeodactylum tricornutum, a model species of microalgae. The source of biotic stress used in this study was 2E,4E/Z-decadienal, a diatom-derived oxylipin that has been shown to function as a stress signal among diatoms. Real-time RT-qPCR analysis revealed that expression of a patatin-like phospholipase was significantly decreased in decadienal-treated cultures as compared to a solvent control. The expression of a delta-9 desaturase gene believed to be responsible for production of 16:1 fatty acids was increased by a factor of 12. FabI, a gene involved in fatty acid biosynthesis, and PtD5a, which codes for an ER-localized desaturase, were both down-regulated in cells exposed to decadienal. However, changes in expression were only shown to be significant for the patatin-like phospholipase gene. Increased expression of the delta-9 desaturase gene may be a protective mechanism against infection from pathogens, since 16:1 fatty acids have been shown to have antibacterial properties. Regulation of membrane desaturation may also serve to stabilize photosynthetic membranes during times of stress. The down-regulation of the phospholipase gene was surprising, since the release of fatty acids from membrane lipids for oxylipin production is a common response to stress. It is recommended that this experiment be improved upon and expanded in order to determine whether the results obtained are reproducible and how these changes in gene expression correlate with physiological effects.Item Effect of temperature, dissolved inorganic carbon and light intensity on the growth rates of two microalgae species in monocultures and co-cultures(2014-05) Almada-Calvo, Fernando; Kinney, Kerry A.; Katz, Lynn E.The enormous biodiversity of microalgae as well as their high photosynthetic rates can be exploited for a wide variety of applications including the production of high value chemicals, nutraceuticals, aquaculture feed, and most recently, biofuels. Regardless of the application, the productivity of the microalgae culture must be optimized in order to make the systems economically feasible. One environmental factor that greatly affects the productivity of mass cultivation systems is temperature since it can be prohibitively expensive to control in outdoor systems. Temperature affects microalgae growth rates both directly by its effect on metabolic rates, and indirectly, by changing the bioavailability of the inorganic carbon present in solution. In the first part of this research, the effects of dissolved inorganic carbon (DIC) concentration (varied by sparging CO₂-enriched air) and temperature on the growth of a model microalga species (Nannochloris sp., UTEX LB1999) were investigated in a turbidostat bioreactor. The results indicate that increasing DIC concentration yields higher microalgae growth rates up to an optimum value (around 3 mM for Nannochloris sp.) but higher concentrations actually inhibited growth. Since increasing the temperature decreases the DIC concentration for a given gas pCO₂, it is necessary to adjust the pCO₂ to maintain the target DIC concentration in the optimal range for growth. In the next phase of the research, the effect of average light intensity (Gav) and temperature on the growth rate of two microalgae species (Nannochloris sp., UTEX1999. and Phaeodactylum tricornutum, UTEX646) was investigated. Growth rates were measured over a range of average light intensities and temperatures using a turbidostat bioreactor. A multiplicative model was developed to describe growth as a function of both average light intensity and temperature. In the third phase of this research, both microalgae species were grown together to explore the effects of temperature fluctuations on the population dynamics of the co-culture. It was observed that Nannochloris was inhibited by the presence of P. tricornutum in the medium, probably due to the excretion of secondary metabolites into the medium that affected Nannochloris growth (allelopathic effects). The temperature and average light intensity model developed under monoculture conditions was modified to incorporate the allelopathic effects observed. The resulting model provided a reasonable fit to the dynamic behavior of a Nannochloris/P. tricornutum co-culture subjected to temperature variations in chemostat experiments.Item Isolation and biological activity of a siderochrome from the blue-green alga, Agmenellum quadruplicatum(1977) Armstrong, James Edward; Van Baalen, C. (Chase), 1925-1986Item pH-induced flocculation/deflocculation process for harvesting microalgae from water(2014-08) Choi, Jin-Yong, Ph. D.; Kinney, Kerry A.; Katz, Lynn Ellen; Kinney, Kerry A.; Katz, Lynn E.Historically, the presence of microalgae (algae hereafter) in natural waters has been viewed as a nuisance due to its adverse impact on water quality. More recently, however, algae are being investigated as potential sources of biofuel and a range of natural products. These applications require the development of large-scale cultivation systems for mass production that include growth, harvesting, concentration, and product recovery components. While challenges still remain with respect to many of the processes involved in mass production, one of the most technically and economically challenging steps is harvesting the algae from dilute growth cultures, especially in systems where chemical additives are of concern either within the algae concentrate or the effluent water. For this reason, a pH-induced flocculation/deflocculation method using the hydroxides of alkali or alkaline earth metals (e.g., lime, caustic soda) is of particular interest for algae harvesting as Na, Ca and Mg are typically present in natural waters. The goal of this research was to determine the underlying mechanisms responsible for algae coagulation by magnesium and calcium and to evaluate the potential of these mechanisms for harvesting algae for a range of synthetic and field source water chemistries. In the first two phases of this research, the mechanisms for coagulation with magnesium and calcium were studied independently. A series of bench-scale experiments were designed to isolate the potential mechanisms of algae destabilization associated with each of these cations as a function of water chemistry, and microscopic analyses were performed to characterize the flocculated algae/precipitate mixtures. In the third phase of this research, removal of algae in field source waters was evaluated with respect to the underlying science elucidated in the previous phases. The results indicate that the dominant algae destabilization mechanism associated with magnesium shifts from Mg adsorption/charge neutralization to Mg(OH)₂[subscript (S)] precipitation-enhanced coagulation with increasing pH. Moreover, dissolved Mg²⁺ adsorption to the algae surface led to effective algae coagulation, while minimizing the mass of precipitated Mg(OH)₂[subscript (S)] . For Ca, this research identified the importance of the nucleation process (heterogeneous vs. homogeneous nucleation) on algae removal efficiency. Heterogeneous nucleation is a key factor for optimizing algae removal; thus, the degree of oversaturation with respect to CaCO₃[subscript (S)] is a crucial operating parameter. This research demonstrated that the algae harvesting process using pH-induced flocculation/deflocculation method can be optimized for a wide range of source waters if the water chemistry (e.g. pH, ion concentration, alkalinity, ionic strength) is properly incorporated into the system design.Item Primary production by microphytobenthos in Corpus Christi Bay, Texas(1988) MacIntyre, Hugh Logan, 1960-; Cullen, John J.The photosynthetic rates of microphytobenthos, those microalgae associated with sediment, were measured in a shallow, turbid bay on the coast of Texas. Rates were determined using a novel technique, appropriate for well-mixed sandy sediments, based on the construction of photosynthesis-irradiance (PI) curves. Photosynthesis-irradiance curves were obtained from ¹⁴C incorporation by suspensions of sediment and were normalized to chlorophyll a. Rates of photosynthesis in situ were calculated from the PI curves and from measured vertical distributions of chlorophyll a and light within the sediment. This technique describes the photosynthetic potential of the microphytobenthos, allowing direct comparison between different strata of the sediment at a single site as well as between different sites. At each site studied, there was a homogeneity of photosynthetic response and biomass that extended well below the photic zone of the sediment, suggesting that the algae in the sediment were mixed vertically. Some evidence that resuspension into the water column is responsible for this homogeneity comes from the vertical differentiation of response and biomass that occurred when sediment was trapped in situ in acrylic cores and from observed fluxes of chlorophyll a and suspended particulate matter in the water column. Because the photosynthetic capacity of the microphytobenthos was similar to that of the algae in the water column, the microphytobenthos may have an important role in net production budgets when resuspended as well as when settled. The sediment may therefore function as a reservoir of photosynthetically-competent algae. The photosynthetic potential and biomass of the microphytobenthos varied on a small spatial scale, as did the rates of photosynthesis realized. Measured hourly rates of microphytobenthic production were 6-62 mg C·m⁻²·h⁻¹. Daily rates were 95-480 mg C·m⁻²·d⁻¹