Synergistic degradation of lignocellulose by fungi and bacteria in boreal forest soil

Thesis (M.S.) University of Alaska Fairbanks, 2015Boreal forests contain an estimated 28% of the world's soil carbon, and currently act as a significant global carbon sink. Plant-derived lignocellulose is a major component of soil carbon, and its decomposition is dependent on soil bacteria and fungi. In order to predict the fate of this soil carbon and its potential feedbacks to climate change, the identities, activity, and interactions of soil microbial decomposer communities must be better understood. This study used stable isotope probing (SIP) with ¹³C-labeled lignocellulose and two of its constituents, cellulose and vanillin, to identify microbes responsible for the processing of lignocellulose-derived carbon and examine the specific roles that they perform. Results indicate that multiple taxa are involved in lignocellulose processing, and that certain taxa target specific portions of the lignocellulose macromolecule; specifically, fungi dominate the degradation of lignocellulose and cellulose macromolecules, while bacteria scavenge aromatic lignocellulose monomers. Major fungal taxa involved in lignocellulose degradation include Ceratobasidium, Geomyces, and Sebacina, among others. Bacterial taxa processing lignocellulose and cellulose included Cellvibrio and Mesorhizobium in high abundance relative to other taxa, although Burkholderia were the primary vanillin consumers. These results elucidate some of the major players in lignocellulose decomposition and their specific roles in boreal forest soil. This information provides knowledge of small-scale microbial processes that dictate ecosystem-level carbon cycling, and can assist in predictions of the fate of boreal forest carbon stocks

Shifts in Fox Den Occupancy in the Greater Prudhoe Bay Area, Alaska

Although shifts in the distribution of red foxes into areas previously dominated by Arctic foxes have been documented over wide areas of the circumpolar North, no such documentation exists yet for the Alaskan Arctic. Fox research in the greater Prudhoe Bay area from the 1970s through the early 1990s focused primarily on Arctic foxes in relation to oil development because red foxes were uncommon. A monitoring program in 2005–12 included annual surveys of 31–48 fox dens within 2 km of the road system. In 2005, 2006, and 2008, Arctic fox dens outnumbered those of red foxes, but from 2010 onward, the reverse was true. There is greater distance between natal dens of Arctic foxes and those of red foxes than between natal dens within each species, suggesting that Arctic foxes avoid red fox denning territories. Of dens in our study that were used by Arctic foxes prior to 2005, 50% have since been occupied by red foxes. Red foxes displaced Arctic foxes from dens closest to oil field camps, pads, and other facilities, and preyed on their pups. Access to anthropogenic food sources probably supports red foxes in the area. Predictions from climate change studies indicate the displacement of Arctic foxes by red foxes will continue in the Alaskan Arctic, although the change may be slower away from areas of human occupation and anthropogenic foods.Malgré que des changements sur le plan de la répartition du renard roux dans des régions qui étaient auparavant dominées par le renard arctique aient été répertoriés dans une grande partie du Nord circumpolaire, ce n’est pas encore le cas de l’Arctique alaskien. L’étude des renards de la grande région de la baie Prudhoe, des années 1970 jusqu’au début des années 1990, portait principalement sur le renard arctique dans le cadre de la mise en valeur du pétrole, car le renard roux n’était pas courant à ce moment-là. Un programme de surveillance mené à bien de 2005 à 2012 a notamment pris la forme de dénombrements annuels de 31 à 48 tanières de renards dans un rayon de deux kilomètres du réseau routier. En 2005, en 2006 et en 2008, le nombre de tanières de renards arctiques dépassait le nombre de tanières de renards roux, mais à partir de 2010, c’était l’inverse. La distance qui sépare les tanières de mise bas des renards arctiques de celles des renards roux est plus grande que la distance qui sépare les tanières de mise bas au sein de chacune des espèces, ce qui laisse entendre que le renard arctique évite les territoires de mise bas du renard roux. Parmi les tanières visées par notre étude qui étaient utilisées par les renards arctiques avant 2005, 50 % d’entre elles sont depuis occupées par des renards roux. Les renards roux ont supplanté les renards arctiques qui occupaient les tanières situées plus près des campements de champs pétrolifères, des zones tampons et d’autres installations, et ils ont attaqué leurs petits. L’accès aux sources alimentaires anthropiques permet probablement au renard roux de survivre dans cette région. Les prévisions émanant des études du changement climatique laissent présager que la supplantation du renard arctique par le renard roux s’étendra à l’Arctique alaskien, bien que le changement puisse se produire plus lentement en raison de l’éloignement de l’occupation humaine et de la nourriture anthropique

The Edge-Connectivity of Vertex-Transitive Hypergraphs

A graph or hypergraph is said to be vertex-transitive if its automorphism group acts transitively upon its vertices. A classic theorem of Mader asserts that every connected vertex-transitive graph is maximally edge-connected. We generalise this result to hypergraphs and show that every connected linear uniform vertex-transitive hypergraph is maximally edge-connected. We also show that if we relax either the linear or uniform conditions in this generalisation, then we can construct examples of vertex-transitive hypergraphs which are not maximally edge-connected.Comment: 8 page

Existential Closure in Line Graphs

A graph $G$ is $n$-existentially closed if, for all disjoint sets of vertices $A$ and $B$ with $|A\cup B|=n$, there is a vertex $z$ not in $A\cup B$ adjacent to each vertex of $A$ and to no vertex of $B$. In this paper, we investigate $n$-existentially closed line graphs. In particular, we present necessary conditions for the existence of such graphs as well as constructions for finding infinite families of such graphs. We also prove that there are exactly two $2$-existentially closed planar line graphs. We then consider the existential closure of the line graphs of hypergraphs and present constructions for $2$-existentially closed line graphs of hypergraphs.Comment: 13 pages, 2 figure

An Integrated Approach to Studying Rare Neuromuscular Diseases Using Animal and Human Cell-Based Models.

As sequencing technology improves, the identification of new disease-associated genes and new alleles of known genes is rapidly increasing our understanding of the genetic underpinnings of rare diseases, including neuromuscular diseases. However, precisely because these disorders are rare and often heterogeneous, they are difficult to study in patient populations. In parallel, our ability to engineer the genomes of model organisms, such as mice or rats, has gotten increasingly efficient through techniques such as CRISPR/Cas9 genome editing, allowing the creation of precision human disease models. Suc

Brane gas-driven bulk expansion as a precursor stage to brane inflation

We propose a new way of obtaining slow-roll inflation in the context of higher dimensional models motivated by string and M theory. In our model, all extra spatial dimensions are orbifolded. The initial conditions are taken to be a hot dense bulk brane gas which drives an initial phase of isotropic bulk expansion. This phase ends when a weak potential between the orbifold fixed planes begins to dominate. For a wide class of potentials, a period during which the bulk dimensions decrease sufficiently slowly to lead to slow-roll inflation of the three dimensions parallel to the orbifold fixed planes will result. Once the separation between the orbifold fixed planes becomes of the string scale, a repulsive potential due to string effects takes over and leads to a stabilization of the radion modes. The conversion of bulk branes into radiation during the phase of bulk contraction leads to reheating.Comment: 5 pages, no figures, same as published on

Highly migratory shark fisheries research by the National Shark Research Consortium (NSRC), 2002-2007

The National Shark Research Consortium (NSRC) includes the Center for Shark Research at Mote Marine Laboratory, the Pacific Shark Research Center at Moss Landing Marine Laboratories, the Shark Research Program at the Virginia Institute of Marine Science, and the Florida Program for Shark Research at the University of Florida. The consortium objectives include shark-related research in the Gulf of Mexico and along the Atlantic and Pacific coasts of the U.S., education and scientific cooperation

Molybdenum Complexes of Chiral C2-symmetric Picchxn-type Ligands: Synthesis, Characterization, and Structural Studies

A series of molybdenum complexes based on chiral C2-symmetric picchxn-type ligands (N4 ligands, defined as trans-N,N′-bis(heterocycl-2-ylmethyl)-1,2-diaminocyclohexanes) has been synthesized and characterized. Reported and novel picchxn-type ligands form (κ3-N4)Mo(CO)3, [(κ4-N4)Mo(NO)(CO)]PF6, and [(κ4-N4)Mo(NO)X]PF6 (X = Br, I) compounds. Multiple tridentate (κ3) and tetradentate (κ4) ligand configurations were observed, and the favored κ4 configuration was found to vary with N4 heterocycle identity. Heterocycle variation allowed for directed modification of the molybdenum electronic characteristics, but none of the studied {(κ4-N4)Mo(NO)}+ fragments was found to be a suitable π-base for dearomatization chemistry. The crystal structures of eight molybdenum complexes with picchxn-type ligands were determined

Improving Predictions for Helium Emission Lines

We have combined the detailed He I recombination model of Smits with the collisional transitions of Sawey & Berrington in order to produce new accurate helium emissivities that include the effects of collisional excitation from both the 2 (3)S and 2 (1) S levels. We present a grid of emissivities for a range of temperature and densities along with analytical fits and error estimates. Fits accurate to within 1% are given for the emissivities of the brightest lines over a restricted range for estimates of primordial helium abundance. We characterize the analysis uncertainties associated with uncertainties in temperature, density, fitting functions, and input atomic data. We estimate that atomic data uncertainties alone may limit abundance estimates to an accuracy of 1.5%; systematic errors may be greater than this. This analysis uncertainty must be incorporated when attempting to make high accuracy estimates of the helium abundance. For example, in recent determinations of the primordial helium abundance, uncertainties in the input atomic data have been neglected.Comment: ApJ, accepte