Browsing by Author "Li, Yang"
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Item Analysis of bacterial-host interactions in Wolbachia infection(2016-05) Li, YangWolbachia (Rickettsiales: Anaplasmataceae) is a genus of cytoplasmically inherited alpha-proteobacterium that infects arthropods (especially insects) and filarial nematodes. In arthropods, upon infection, Wolbachia alters the host reproduction in a variety of ways including cytoplasmic incompatibility, parthenogenesis, male-killing and feminization to enhance its own transmission. My doctoral research has been focusing on molecular and biochemical interactions between Wolbachia and its arthropod host. In chapter one, I made an introduction of Wolbachia including its biology, phylogeny and potential in disease control. I also reviewed the studies on Wolbachia-host interactions with an emphasis on Wolbachia Type IV Secretion System (T4SS). In chapter two, I presented the research I carried out in order to understand Wolbachia-mosquito interactions through T4SS. I molecular cloned the T4SS coupling protein VirD4 from wPip and analyzed the co-transcription between T4SS and Wolbachia surface protein in wStr. In chapter three, I amplified and sequenced five ribosomal protein (rp) genes of wFol from its host Folsomia candida, and phylogenetic analyzed 17 Wolbachia strains based on the available rp sequences. I also detected a DNase activity in isolated F. candida DNA. In chapter four, I further studied the DNase activity that co-purified with F. candida DNA, including characterizing the DNase active conditions and estimating the molecular weight of the DNase. In chapter five, I described an approach to estimate the biomass of F. candida with a protein stain, Ponceau S.Item Berkovich nanoindentation and FTIR data describing the effect of water on olivine plasticity(2023-08-28) Kumamoto, Kathryn, M; Breithaupt, Thomas, P; Hansen, Lars, N; Wallis, David; Li, Bo-Shiuan; Armstrong, David, EJ; Goldsby, David, L; Li, Yang; Warren, Jessica, M; Wilkinson, Angus, J; lnhansen@umn.edu; Hansen, Lars, N; Rock and Mineral Physics LabThis data set contains data collected as part of a study to determine the influence of dissolved hydrogen on the mechanical properties of olivine. Nanoindentation experiments were conducted to measure the hardness of both pristine olivine crystals and olivine crystals predoped with hydrogen. The hydrogen content of samples was assessed with Fourier-transform infrared spectroscopy (FTIR). This data set includes mechanical data from indentation experiments as well as spectra from FTIR measurements.Item Deciphering Cryptic Stereochemistry in Polyketide Biosynthesis and Functional Characterization of β-processing Domains in Pikromycin Synthase(2015-07) Li, YangCombinatorial biosynthesis of polyketides through engineering the respective biosynthetic pathways represents a promising approach to natural products discovery. However, a lack of information on substrate and stereochemical specificity of polyketide synthases (PKS) currently hinders these efforts. Though recent research in the area has provided many mechanistic revelations, a basic-level understanding of kinetic and substrate tolerability is still needed before the full potential of combinatorial biosynthesis can be realized. We have developed a novel set of chemical probes for the study of ketoreductase (KR) and dehydratase (DH) domains of PKS. PKS KRs stereoselectively reduce the β-keto chain intermediate while dictating the orientation of the α-substituent. The DHs of PKS, which generate an α,β-unsaturated bond through dehydration of a β-alcohol, have extremely high stereospecficity towards substrates and can prematurely terminate the nascent polyketide when presented with unnatural substrates. We have developed a chemical tool-based approach which was verified using KR and DH of pikromycin PKS module 2 (PikKR2) as a model system. Triketide substrate mimics were designed to increase stability (incorporating a non-hydrolyzable thioether linkage) and minimize non-essential functionality (truncating the phosphopantetheinyl arm). The identities of reduction and dehydration products as well as steady-state kinetic parameters were revealed by a LC-MS/MS analysis of synthetic standards. Additionally, the substrate specificity was interrogated with a systematic series of synthetic triketides containing altered stereogenic centers. Furthermore, the mechanism of PikDH2 catalyzed dehydration was investigated by site-directed mutagenesis, evaluation of the pH dependence of catalytic efficiency (Vmax/KM), and through kinetic characterization of a mechanism-based inhibitor.Item Hydrogen incorporation mechanisms and diffusion of hydrous defects and silicon ions in olivine: the major rock-forming mineral of the Earth's upper mantle(2015-12) Li, YangWater solubility of olivine was investigated with controlled pyroxene activity at 0.3 to 5 GPa and 1473 K. Its dependence on pyroxene activity and water fugacity with the activation volume was studies to place constraints on the hydrogen incorporation mechanisms in olivine. Results of water solubility in olivine indicate that hydrogen incorporated with metal vacancies is the dominant mechanism for samples buffered with pyroxene at all pressures. Hydration and dehydration experiments were carried out to study the kinetic properties of hydrogen ions in olivine to determine the diffusivity of hydrous defects associated with individual peaks in IR spectra. Results of diffusivity indicate that hydrogen diffuses in olivine as interstitial hydrogen ions regardless of the incorporation mechanisms. Silicon diffusivity was also study to better understand the point defect chemistry of olivine.Item Summary of Breeding Bird Trends in the Chippewa and Superior National Forests of Minnesota: 1995-2014(University of Minnesota Duluth, 2014) Zlonis, Edmund J; Grinde, Alexis R; Condon, Elizabeth; Panci, Hannah; Li, Yang; Regal, Ronald R; Niemi, Gerald JA total of 329 existing forest stands were surveyed for breeding birds including 135 and 194 stands (953 survey points) in the Chippewa and Superior National Forests (NFs), respectively in 2014.