283 research outputs found
Development of a novel system for isolating genes involved in predator-prey interactions using host independent derivatives of Bdellovibrio bacteriovorus 109J
<p>Abstract</p> <p>Background</p> <p><it>Bdellovibrio bacteriovorus </it>is a gram-negative bacterium that preys upon other gram-negative bacteria. Although the life cycle of <it>Bdellovibrio </it>has been extensively investigated, very little is known about the mechanisms involved in predation.</p> <p>Results</p> <p>Host-Independent (HI) mutants of <it>B. bacteriovorus </it>were isolated from wild-type strain 109J. Predation assays confirmed that the selected HI mutants retained their ability to prey on host cells grown planktonically and in a biofilm. A mariner transposon library of <it>B. bacteriovorus </it>HI was constructed and HI mutants that were impaired in their ability to attack biofilms were isolated. Transposon insertion sites were determined using arbitrary polymerase chain reaction. Ten HI transposon mutants mapped to genes predicted to be involved in mechanisms previously implicated in predation (flagella, pili and chemotaxis) were further examined for their ability to reduce biofilms.</p> <p>Conclusion</p> <p>In this study we describe a new method for isolating genes that are required for <it>Bdellovibrio </it>biofilm predation. Focusing on mechanisms that were previously attributed to be involved in predation, we demonstrate that motility systems are required for predation of bacterial biofilms. Furthermore, genes identified in this study suggest that surface gliding motility may also play a role in predation of biofilms consistent with Bdellovibrios occupying a biofilm niche. We believe that the methodology presented here will open the way for future studies on the mechanisms involved in <it>Bdellovibrio </it>host-prey interaction and a greater insight of the biology of this unique organism.</p
A Serratia marcescens OxyR Homolog Mediates Surface Attachment and Biofilm Formation
OxyR is a conserved bacterial transcription factor with a regulatory role in oxidative stress response. From a genetic screen for genes that modulate biofilm formation in the opportunistic pathogen Serratia marcescens, mutations in an oxyR homolog and predicted fimbria structural genes were identified. S. marcescens oxyR mutants were severely impaired in biofilm formation, in contrast to the hyperbiofilm phenotype exhibited by oxyR mutants of Escherichia coli and Burkholderia pseudomallei. Further analysis revealed that OxyR plays a role in the primary attachment of cells to a surface. Similar to what is observed in other bacterial species, S. marcescens OxyR is required for oxidative stress resistance. Mutations in oxyR and type I fimbrial genes resulted in severe defects in fimbria-associated phenotypes, revealing roles in cell-cell and cell-biotic surface interactions. Transmission electron microscopy revealed the absence of fimbria-like surface structures on an OxyR-deficient strain and an enhanced fimbrial phenotype in strains bearing oxyR on a multicopy plasmid. The hyperfimbriated phenotype conferred by the multicopy oxyR plasmid was absent in a type I fimbrial mutant background. Real-time reverse transcriptase PCR indicated an absence of transcripts from a fimbrial operon in an oxyR mutant that were present in the wild type and a complemented oxyR mutant strain. Lastly, chromosomal Plac-mediated expression of fimABCD was sufficient to restore wild-type levels of yeast agglutination and biofilm formation to an oxyR mutant. Together, these data support a model in which OxyR contributes to early stages of S. marcescens biofilm formation by influencing fimbrial gene expression
Principal forms X^2 + nY^2 representing many integers
In 1966, Shanks and Schmid investigated the asymptotic behavior of the number
of positive integers less than or equal to x which are represented by the
quadratic form X^2+nY^2. Based on some numerical computations, they observed
that the constant occurring in the main term appears to be the largest for n=2.
In this paper, we prove that in fact this constant is unbounded as n runs
through positive integers with a fixed number of prime divisors.Comment: 10 pages, title has been changed, Sections 2 and 3 are new, to appear
in Abh. Math. Sem. Univ. Hambur
Geological and thermal control of the hydrothermal system in northern Yellowstone Lake: inferences from high-resolution magnetic surveys
Author Posting. © American Geophysical Union, 2020. This article is posted here by permission of American Geophysical Union for personal use, not for redistribution. The definitive version was published in Journal of Geophysical Research: Solid Earth 125(9), (2020): e2020JB019743, doi:10.1029/2020JB019743.A multiscale magnetic survey of the northern basin of Yellowstone Lake was undertaken in 2016 as part of the Hydrothermal Dynamics of Yellowstone Lake Project (HDâYLAKE)âa broad research effort to characterize the causeâandâeffect relationships between geologic and environmental processes and hydrothermal activity on the lake floor. The magnetic survey includes lake surface, regional aeromagnetic, and nearâbottom autonomous underwater vehicle (AUV) data. The study reveals a strong contrast between the northeastern lake basin, characterized by a regional magnetic low punctuated by stronger local magnetic lows, many of which host hydrothermal vent activity, and the northwestern lake basin with higherâamplitude magnetic anomalies and no obvious hydrothermal activity or punctuated magnetic lows. The boundary between these two regions is marked by a steep gradient in heat flow and magnetic values, likely reflecting a significant structure within the currently active ~20âkmâlong Eagle BayâLake Hotel fault zone that may be related to the ~2.08âMa Huckleberry Ridge caldera rim. Modeling suggests that the broad northeastern magnetic low reflects both a shallower Curie isotherm and widespread hydrothermal activity that has demagnetized the rock. Along the western lake shoreline are sinuousâshaped, highâamplitude magnetic anomaly highs, interpreted as lava flow fronts of upper units of the West Thumb rhyolite. The AUV magnetic survey shows decreased magnetization at the periphery of the active Deep Hole hydrothermal vent. We postulate that lower magnetization in the outer zone results from enhanced hydrothermal alteration of rhyolite by hydrothermal condensates while the vaporâdominated center of the vent is less altered.The lake surface and AUV magnetic data were acquired under National Park Service research permit YELLâ2016âSCIâ7018 and the 2016 aeromagnetic data under research permit YELLâ2016âSCIâ7056. We thank Sarah Haas, Stacey Gunther, Erik Oberg, Annie Carlson, and Patricia Bigelow at the Yellowstone Center for Resources for assistance with permitting and logistics, Ranger Jackie Sene for assistance with logistics and safety at Bridge Bay, Bob Gresswell for providing us with the U.S. Geological Survey (USGS) boat Alamar, the boat pilot Nick Heredia, and Robert Harris and Shaul Hurwitz for fruitful discussions. We are very thankful to Ocean Floor Geophysics (Brian Claus and Steve Bloomer) who provided the magnetometer for the AUV survey and preprocessed the data, and to the REMUS 600 team (Greg Packard and Greg Kurras) for operating and optimizing the AUV during lake operations. Data from the Newport and Boulder observatories were used to process the survey data. We thank the USGS Geomagnetism Program for supporting their operation and INTERMAGNET for promoting high standards of magnetic observatory practice (www.intermagnet.org). This research was funded by the National Science Foundation's Integrated Earth Systems program EARâ1516361 (HDâYLAKE project), USGS Mineral Resource and Volcano Hazard Programs, and benefited from major inâkind support from the USGS Yellowstone Volcano Observatory. Maurice Tivey was supported under National Science Foundation Grant OCEâ1557455. During the course of this study, Claire Bouligand was a visiting scientist at the USGS in Menlo Park, California, USA, benefited from a delegation to Centre National de la Recherche Scientifique (CNRS), and received funding from CNRSâINSU program SYSTER. ISTerre is part of Labex OSUG@2020 (ANR10 LABX56). Any use of trade, firm, or product names is for descriptive purposes and does not imply endorsement by the U.S. Government.2021-01-2
Malaria in Kenya's Western Highlands
Reemergence of epidemics in tea plantations will likely result in antimalarial-drug resistance
The SolventâSolid Interface of Acid Catalysts Studied by High Resolution MAS NMR
High-resolution magic angle spinning (HRMAS) NMR spectroscopy was used to study the eïŹect of mixed solvent systems on the acidity at the solidâliquid interface of solid acid catalysts. A method was developed that can exploit beneïŹts of both solution and solid-state NMR (SSNMR) by wetting porous solids with small volumes of liquids (ÎŒL/mg) to create an interfacial liquid that exhibits unique motional dynamics intermediate to an isotropic liquid and a rigid solid. Results from these experiments provide information about the inïŹuence of the solvent mixtures on the acidic properties at a solidâliquid interface. Importantly, use of MAS led to spectra with full resolution between water in an acidic environment and that of bulk water. Using mixed solvent systems, the chemical shift of water was used to compare the relative acidity as a function of the hydration level of the DMSO-d6 solvent. Nonlinear increasing acidity was observed as the DMSO-d6 became more anhydrous. 1H HR-MAS NMR experiments on a variety of supported sulfonic acid functionalized materials, suggest that the acid strength and number of acid sites correlates to the degree of broadening of the peaks in the 1H NMR spectra. When the amount of liquid added to the solid is increased (corresponding to a thicker liquid layer), fully resolved water phases were observed. This suggests that the acidic proton was localized predominantly within a 2 nm distance from the solid. EXSY 1Hâ1H 2D experiments of the thin layers were used to determine the rate of proton exchange for diïŹerent catalytic materials. These results demonstrated the utility of using (SSNMR) on solidâliquid mixtures to selectively probe catalyst surfaces under realistic reaction conditions for condensed phase systems
The Statistical Approach to Quantifying Galaxy Evolution
Studies of the distribution and evolution of galaxies are of fundamental
importance to modern cosmology; these studies, however, are hampered by the
complexity of the competing effects of spectral and density evolution.
Constructing a spectroscopic sample that is able to unambiguously disentangle
these processes is currently excessively prohibitive due to the observational
requirements. This paper extends and applies an alternative approach that
relies on statistical estimates for both distance (z) and spectral type to a
deep multi-band dataset that was obtained for this exact purpose.
These statistical estimates are extracted directly from the photometric data
by capitalizing on the inherent relationships between flux, redshift, and
spectral type. These relationships are encapsulated in the empirical
photometric redshift relation which we extend to z ~ 1.2, with an intrinsic
dispersion of dz = 0.06. We also develop realistic estimates for the
photometric redshift error for individual objects, and introduce the
utilization of the galaxy ensemble as a tool for quantifying both a
cosmological parameter and its measured error. We present deep, multi-band,
optical number counts as a demonstration of the integrity of our sample. Using
the photometric redshift and the corresponding redshift error, we can divide
our data into different redshift intervals and spectral types. As an example
application, we present the number redshift distribution as a function of
spectral type.Comment: 40 pages (LaTex), 21 Figures, requires aasms4.sty; Accepted by the
Astrophysical Journa
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