Browsing by Subject "Cyanobacteria"
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Item A Study on Biological Threats to Texas Freshwater Resources(2014-01-15) Neisch, MichaelThis thesis consists of two separate experiments on unique biological threats to Texas freshwater ecosystems. The first experiment sought to understand the interaction between the harmful alga Prymnesium parvum and the cyanobacteria, Anabaena sp. The second experiment sought to determine the effectiveness of triploid grass carp, Ctenopharyngodon idella, as a biological control for two species of invasive macrophytes, which were giant salvinia, Salvinia molesta, and hygrophila, Hygrophila polysperma. Prymnesium parvum blooms have become more frequent in the south-central United States, leading to significant ecological and economic impacts. Allelopathic effects from cyanobacteria were suggested as a mechanism that might limit the development of P. parvum blooms. This research focused on the effects of cultured cyanobacteria, Anabaena sp., on P. parvum. Over a 6-d period, daily additions of filtrate from the senescent Anabaena culture were made to P. parvum cultures growing in log phase. All treatments, including several types of controls, showed reductions in P. parvum biomass over the course of the experiment, but the treatments receiving Anabaena filtrate were reduced to a lesser degree, suggesting that filtrate from the senescent cyanobacteria culture was beneficial to P. parvum in some way. Aquatic vegetation is an important component of most freshwater systems and provides numerous valuable ecosystem services, providing food, habitat and refuge for a variety of organisms. A significant threat to beneficial aquatic vegetation abundant in many United States waterways is the introduction and spread of invasive macrophytes. Two of the newest invasive species, giant salvinia (Salvinia molesta) and hygrophila (Hygrophila polysperma), have quickly established in Texas waters. This research evaluated the potential use of triploid grass carp (Ctenopharyngodon idella) as a biological control agent for these two novel invasive species. Using a controlled mesocosm experiment, consumption rates and feeding preferences were measured. Giant salvinia and hygrophila were compared to six native and introduced species common in Texas and the Southern US. Grass carp were found to be potentially useful in controlling giant salvinia in the preliminary stages of an infestation but an overall poor control option for hygrophila.Item Arsenate uptake, sequestration and reduction by a freshwater cyanobacterium: a potenial biologic control of arsenic in South Texas(Texas A&M University, 2005-08-29) Markley, Christopher ThomasThe toxicity and adverse health effects of arsenic are widely known. It is generally accepted that sorption/desorption reactions with oxy-hydroxide minerals (iron, manganese) control the fate and transport of inorganic arsenic in surface waters through adsorption and precipitation-dissolution processes. In terrestrial environments with limited reactive iron, recent data suggest organoarsenicals are potentially important components of the biogeochemical cycling of arsenic in near-surface environments. Elevated arsenic levels are common in South Texas from geogenic processes (weathering of As-containing rock units) and anthropogenic sources (a byproduct from decades of uranium mining). Sediments collected from South Texas show low reactive iron concentrations, undetectable in many areas, making oxy-hydroxide controls on arsenic unlikely. Studies have shown that eukaryotic algae isolated from arsenic-contaminated waters have increased tolerance to arsenate toxicity and the ability to uptake and biotransform arsenate. In this experiment, net uptake of arsenic over time by a freshwater cyanobacterium never previously exposed to arsenate was quantified as a function of increasing As concentrations and increasing N:P ratios. Toxic effects were not evident when comparing cyanobacterial growth, though extractions indicate accumulation of intracellular arsenic by the cyanobacterium. Increasing N:P ratios has minimal effect on net arsenate uptake over an 18 day period. However, cyanobacteria were shown to reduce arsenate at rates faster than the system can re-oxidize the arsenic suggesting gross arsenate uptake may be much higher. Widespread arsenate reduction by cyanobacterial blooms would increase arsenic mobility and potential toxicity and may be useful as a biomarker of arsenic exposure in oxic surface water environments.Item Bacterial cellulose in cyanobacteria : enhancement of cellulose production in Synechococcus elongatus with Gluconacetobacter xylinus transgenes(2014-12) Sessler, Tate Hopkins; Brown, R. (Richard Malcolm), 1939-Bacterial cellulose produced by Gluconacetobacter xylinus possesses an abundance of desirable properties which allow for commercial applications in manufacturing, construction, medicine, as a biofuel feedstock and in electronics as an electrical insulator. Large scale production methods are currently limited by expensive media and requirements for sterile conditions. This thesis investigates the potential for using cellulose synthesized by cyanobacteria as an alternative. Cyanobacteria require fewer media components, fix atmospheric carbon dioxide, and some species fix atmospheric nitrogen, reducing the demand for fertilizer and lowering contamination potential. In this study, a suite of genes involved with cellulose synthesis in G. xylinus were successfully transferred to into the unicellular cyanobacterium, Synechococcus elongatus. Cellulose synthesis was increased in multiple transgenic strains by 300-400% and cellulose microfibrils were observed with enhanced crystallization upon addition of the acsCD transgene from G. xylinus. The evolutionary history of the proteins involved in cellulose synthesis was also investigated, with particular interest paid toward the catalytic subunit. It was determined that all current organisms with the capability of cellulose assembly possess synthases from a single ancestral origin at least 2.5 billion years ago. This work provides additional support to the theory that vascular plants acquired cellulose synthases from cyanobacteria.Item Cellulose in the cyanobacteria(2006) Nobles, David Ronald; Brown, R. Malcolm (Richard Malcolm), 1939-Item Characterization of ferredoxin-dependent enzymes from plants and cyanobacteria(Texas Tech University, 1988-08) Sung, Jeou-derNot availableItem Coordinated response and regulation of carotenogenesis in Thermosynechococcus elongatus (BP-1) : implications for commercial application(2014-12) Knight, Rebecca Anne; Brand, Jerry J. (Jerry Jay), 1941-; Alper, Hal S.If small isoprenoids, the starting component of carotenoids, can be efficiently excreted from thermophilic cyanobacteria, they could help satisfy the demand for sustainably produced hydrocarbons. This is the driving force behind wanting to understand the response and regulation of isoprenoid pathways to environmental stimuli in the thermophilic cyanobacterium, Thermosynechococcus elongatus, BP-1. The portion of the isoprenoid pathway studied here is the carotenoid pathway since these products are critical to adaptation and they encompass the largest pool of isoprenoid compounds in cyanobacteria. Although synthetic biology in cyanboacteria has improved in recent years, there are many undiscovered metabolic complexities that make large-scale commercial production challenging. To address this need, I quantify and report for the first time metabolic shifts within the carotenoid pathway of BP-1 due to combined effects of temperature, pH and blue light. I show that metabolism shifts from the dicyclic into the monocyclic carotenoid pathway in response to pH, and that decreasing temperature drives flux into the end products of both pathways. Also, I report that the productivity of an uncommon carotenoid, 2-hydroxymyxol 2’-fucoside (HMF), approached 500 μg/L-day in cultures grown at 45 °C, high light intensity, and pH 8. In order to further elucidate these responses, I analyzed 42 RNAseq samples taken over time of BP-1 induced by cold and heat stress and compared these results to metabolomics data. I showed that crtR and crtG, two central carotenogenesis genes, are transcriptionally controlled and used weighted gene co-expression network analysis (WGCNA) to determine eight separate co-expressed modules of biological significance. Among the co-regulated heat response and cold response genes there were three and five non-coding RNA, respectively, providing targets for future investigation. Using subtractive genomics and transcriptional data I narrowed the potential missing steps of the myxol pathway in cyanobacteria to seven unknown BP-1 genes, two of which were confirmed not to be involved in the missing step(s). Finally, by generating a ΔcrtG mutant and testing it under different environmental parameters, I showed that HMF does not protect against high pH or low temperature (despite up-regulation at these conditions), and that CrtG has a higher affinity for monocyclic than dicyclic carotenoids.Item Heterocyst Morphogenesis and Gene Expression in Anabaena sp. PCC 7120(2010-10-12) Mella Herrera, Rodrigo AndresMany multicellular cyanobacteria produce specialized nitrogen-fixing heterocysts. During diazotrophic growth of the model organism Anabaena (Nostoc) sp. strain PCC 7120, a regulated developmental pattern of single heterocysts separated by about 10 to 20 photosynthetic vegetative cells is maintained along filaments. Heterocyst structure and metabolic activity function to accommodate the oxygen-sensitive process of nitrogen fixation. This dissertation focuses on my research on heterocyst development, including morphogenesis, transport of molecules between cells in a filament, differential gene expression, and pattern formation. We using microarray experiments we found that conR (all0187) gene is necessary for normal septum-formation of vegetative cells, diazotrophic grow, and heterocyst morphogenesis. In our studies we characterized the expression of sigma factors genes in Anabaena PCC 7120 during heterocyst differentiation, and we found that the expression of sigC, sigG and sigE is localized primarily in heterocysts. Expression studies using sigE mutant showed that nifH is under the control of this specific sigma factor.Item Influence of major storm events on the quantity and composition of particulate organic matter in the Mission-Aransas Estuary(2016-12) Reyna, Nicolas Eduardo; Hardison, Amber K.; Liu, ZhanfeiVariations in the freshwater inflow regimes of estuaries, due to perturbations such as storm events, alter the source and composition of particulate organic matter (POM), which represents the base of the food web, including available energy resources for secondary production. To evaluate the impact of varying freshwater discharge on POM quantity and composition, monthly samples of surface water were collected at four long term monitoring stations from 2012-2015 in the Mission-Aransas Estuary in subtropical Texas, which is characterized by a semiarid climate, drought, and sporadic precipitation events that affect water quality of the system. We analyzed organic carbon and nitrogen concentrations, carbon and nitrogen stable isotope ratios, and pigment concentrations of the POM samples. Following a prolonged dry spell, consecutive major storm events in spring 2015 led to a dramatic freshening of the entire estuary. Large increases in particulate organic carbon (POC) concentrations and decreases in δ¹³C values of POC over several weeks following the storms suggest an increase in in-situ production at lower salinities as a result of increased inflows. These changes in bulk POM coincided with an increase in chlorophyll a concentration, further indicating a significant contribution by phytoplankton to the elevated POM. Concurrently, pigment biomarkers revealed a significant (10-fold) increase in the cyanobacterial pigment, zeaxanthin, and further 16S rRNA analysis showed that Cyanobium spp. was responsible for the observed bloom. The combination of environment conditions, including freshening, high temperature and high nutrients, likely contributed to the cyanobacteria bloom. These results show episodic rain events can substantially affect estuarine phytoplankton community composition, which impacts the available energy resources for secondary production and thus may have ecosystem-wide implications on productivity.Item Microbial community structure and nitrogen cycling in limestone biofilms(2015-08) Hancock, Tinisha; Brand, Jerry J. (Jerry Jay), 1941-; La Claire, John W; Leibold, Mathew A; Mehdy, Mona; Nobles, David RBiofilms inhabiting rock surfaces were of particular interest for this study, due to their ubiquity in central Texas and possible role in nitrogen cycling. Biofilm samples from an ornamental pond in Austin, Texas were collected over the course of two and a half years. Microscopic analysis indicated that the general physical structure of the biofilm remained constant, but the organisms inhabiting the biofilm varied. Metagenomic analysis confirmed that taxonomic diversity in biofilm communities is dynamic and variable, but the predicted functional capacities appear to be relatively stable throughout the sampling time. Less than one quarter of the variation in the taxonomic community data is explained by climate variables, indicating that a combination of stochastic and deterministic factors may drive community assembly. Limestone biofilm communities may be colonized from guilds of organisms that assemble based on the functional requirements prescribed by environmental conditions and resource availability. Natural biofilm samples were collected from other distinct patches of limestone in green spaces near Austin. Natural biofilms were thicker and more complex than the ornamental pond biofilms, yet they were not significantly different from each other in terms of their taxonomic community composition. The functional diversity of the natural biofilms was nearly identical to that seen in the ornamental pond biofilms. Taxonomic and functional diversity in natural biofilms were strongly correlated and significantly dissimilar. A strong negative correlation between actinobacteria abundance and bacteroidetes abundance was found, indicating that these organisms might be competitors. Cyanobacteria abundance was positively correlated with both humidity and precipitation, indicating that cyanobacteria might require more water than other organisms in the biofilm community. Organisms within limestone biofilm communities were capable of fixing atmospheric nitrogen, but the rate of nitrogenase activity was highly variable throughout the sampling period. Nostoc was the most abundant and active nitrogen-fixing organism. The abundance of cyanobacteria capable of fixing nitrogen was prone to fluctuation, whereas the abundance of non-photosynthetic nitrogen fixers remained relatively constant. Nitrogenase activity in the light reflects a combined effort between cyanobacterial and other nitrogen fixers and a consortium of other nitrogen fixers may be solely responsible for nitrogenase activity in the dark.Item The microbial ecology and biogeochemistry of cyanobacteria in the arsenic-rich and inorganic carbon-limited geothermal waters of El Tatio Geyser Field, Chile(2015-05) Myers, Kimberly Dawn; Bennett, Philip C. (Philip Charles), 1959-; Bell, Christopher J; Omelon, Christopher R; Shanahan, Timothy M; Hawkes, Christine VGeothermal settings are some of the best-known analogs for early earth environments and among the best places to investigate the impact of extreme conditions on microbial life. El Tatio Geyser Field (ETGF) is a geothermal setting located at 4,300m in the Atacama Desert region of Chile. Its high-elevation desert position leads to high UV-flux, rapid evaporation, and mineral precipitation. El Tatio geothermal waters also possess extremely limited concentrations of life-essential nutrients, such as dissolved inorganic carbon (DIC as CO2(aq) + HCO3-), contain among the highest naturally occurring concentrations of the toxic element arsenic (As as H3AsO30 + HXAsO43-X), and are buffered to circumneutral pH by arsenate (H2AsO4-/HAsO42-; pKa ~ 6.9 at 25°C). Cyanobacteria were found to be the most important primary producers supporting microbial communities in El Tatio geothermal waters. The objective of this dissertation work was to characterize the role of cyanobacteria in the ETGF microbial ecosystem, and determine the response of cyanobacteria to the high-As and low-DIC conditions present at ETGF. Field observations, geochemical analyses, and next-generation 16S rRNA gene sequencing approaches were used to determine the geochemical controls on cyanobacterial distribution, the phylogenetic diversity of El Tatio cyanobacteria, and the corresponding microbial community structure at sites with and without cyanobacteria. Four cultured cyanobacterial strains were isolated from ETGF mat material, and experiments were performed to assess the growth and carbon-uptake response of these strains to low DIC, AsIII, and AsV. AsIII and temperature negatively controlled the abundance and distribution of cyanobacteria in geothermal outflows throughout ETGF, whereas AsV positively influenced these factors. In the laboratory, AsIII inhibited the growth of cultured strains, while AsV stimulated growth. Closed-system experiments showed significantly increased carbon uptake and growth in the presence of AsV, due to the ability of arsenate to offset the rapid upward pH shift that often occurs in mats during photosynthesis, thereby maintaining DIC in the preferred forms for cyanobacterial uptake. These results showed that AsV plays a positive role in the ETGF microbial ecosystem by increasing the productivity of cyanobacterial mats under low DIC and arsenate-buffered conditions.Item Studies of the cytochrome bc1 complex and its electon acceptors in purple photosynthetic bacteria(Texas Tech University, 2001-12) Li, JunThe cytochrome bc1 complex is a key component of electron transfer chains in mitochondria and in many aerobic and photosynthetic bacteria. The bc1 complexes from photosynthetic bacteria provide many advantages for understanding electron transfer through the complex, as they are structurally simpler than the mitochondrial complexes and fast electron transfer after photoactivation of the reaction center can be easily followed using absorbance changes, something that cannot be done with mitochondria. This dissertation focuses on three aspects related to the bc1 complexes: (1) The role of HiPIP and cytochrome cg, which are reduced by the bc1 complex, as alternative electron donors to the reaction center of Chromatium vinosum. Laser flash kinetics with intact Cm. vinosum cells showed that either HiPIP or cytochrome cg can be an efficient electron donor to the reaction center, depending on the media used to grow the cells. However, the preference for one electron donor over another does not arise from significant differences in protein abundance in the cells grown in the two different media. The mechanism of this "switch" remains to be elucidated. (2) Spectroscopic and oxidation-reduction properties of M183K and M183H variants of Rhodobacter capsulatus cytochrome c8. MCD and EPR spectra suggest that Rb. capsulatus cyt c\ is flexible and that one of the three histidines present outside the normal heme-binding domain can be recruited as an alternative to the methionine heme ligand found in the wild-type cytochrome. Titrations carried out in the oxidative direction differ markedly from those carried out in the reductive direction, mdicating the possible occurrence of redox-triggered conformational changes. (3) Interaction between Rb. capsulatus cytochrome bc1 and equine cytochrome c (a homolog for Rb. capsulatus cytochrome C2). Steady-state kinetic data, using site-specific cyt c1 mutants, showed that one acidic patch on the surface of cytochrome ci is unlikely to be involved in binding to cytochrome c. However, both steady-state kinetics and redox titration revealed that the phenylanaline at position 138 plays a critical role m maintaining a normal heme environment and suggest that this aromatic amino acid may participate in mediating electron transfer to and/or from the heme of cyt c1.Item Synthetic studies related to the marine natural product oscillatoxin D(Texas Tech University, 1997-12) Kahl, Jeffrey DeanOsdllatoxin D is a nontoxic natural product found in tropical marine bluegreen algae which possesses antileukemic activity. This dissertation describes progress towards the synthesis of structurally advanced intermediates for the total synthesis of osdllatoxin D. The overall goal of this research is to test synthetic methodology aimed at streamlining the synthesis of advanced intermediates. This goal was achieved through several objectives. First, attempts were made o resolve antidpated problems with the introduction of y-lactone portion of osdllatoxin D. during the synthesis by the exploration of a novel carboxylic acid protection groups which could be removed under mild conditions. Second, attempts were made to improve the efficiency of a previously described synthesis of a major intermediate for the synthesis of osdllatoxin D. Third, an osdllatoxin D precursor bearing all of the carbon atoms of osdllatoxin D itself was prepared and used to test a hypothetical spirobicyclization reaction which would, if successful, have formed the complete central bicydic portion of osdllatoxin D.