498 research outputs found
Distribution of unionid mussels in tributaries of the Lower Flint River, Southwestern Georgia: an examination of current and historical trends
The historically diverse assemblage of freshwater mussels in the Flint River Basin (FRB) has shown declines in abundance and distribution. The mid-reaches of the major tributaries of the Flint River contained one of the richest assemblages of mussels in the southeastern Coastal Plain. Declines in mussel assemblages were accelerated by the recent drought that occurred during 1999-2001. Following the drought, we surveyed mussel populations at selected sites in the major tributaries of the Flint River to determine if declines in abundance and distribution were continuing. Many populations of common, rare, and endangered species were stable in their distribution but exhibited declines in numbers. One survey site in particular, on Spring Creek, contains a rich assemblage of mussels unique to this basin, and surveys from this site also suggest population declines. Possible explanations for declines include poor water quality, loss or degradation of instream habitat, competition from the exotic Asiatic clam, and inadequate instream flows.Sponsored by:
Georgia Environmental Protection Division
U.S. Geological Survey, Georgia Water Science Center
U.S. Department of Agriculture, Natural Resources Conservation Service
Georgia Institute of Technology, Georgia Water Resources Institute
The University of Georgia, Water Resources Facult
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Scarcity of fixed carbon transfer in a model microbial phototroph–heterotroph interaction
Although the green alga Chlamydomonas reinhardtii has long served as a reference organism, few studies have interrogated its role as a primary producer in microbial interactions. Here, we quantitatively investigated C. reinhardtii's capacity to support a heterotrophic microbe using the established coculture system with Mesorhizobium japonicum, a vitamin B12-producing α-proteobacterium. Using stable isotope probing and nanoscale secondary ion mass spectrometry (nanoSIMS), we tracked the flow of photosynthetic fixed carbon and consequent bacterial biomass synthesis under continuous and diurnal light with single-cell resolution. We found that more 13C fixed by the alga was taken up by bacterial cells under continuous light, invalidating the hypothesis that the alga's fermentative degradation of starch reserves during the night would boost M. japonicum heterotrophy. 15NH4 assimilation rates and changes in cell size revealed that M. japonicum cells reduced new biomass synthesis in coculture with the alga but continued to divide-a hallmark of nutrient limitation often referred to as reductive division. Despite this sign of starvation, the bacterium still synthesized vitamin B12 and supported the growth of a B12-dependent C. reinhardtii mutant. Finally, we showed that bacterial proliferation could be supported solely by the algal lysis that occurred in coculture, highlighting the role of necromass in carbon cycling. Collectively, these results reveal the scarcity of fixed carbon in this microbial trophic relationship (particularly under environmentally relevant light regimes), demonstrate B12 exchange even during bacterial starvation, and underscore the importance of quantitative approaches for assessing metabolic coupling in algal-bacterial interactions
Dynamics of DNA replication loops reveal temporal control of lagging-strand synthesis
In all organisms, the protein machinery responsible for the replication of DNA, the replisome, is faced with a directionality problem. The antiparallel nature of duplex DNA permits the leading-strand polymerase to advance in a continuous fashion, but forces the lagging-strand polymerase to synthesize in the opposite direction. By extending RNA primers, the lagging-strand polymerase restarts at short intervals and produces Okazaki fragments. At least in prokaryotic systems, this directionality problem is solved by the formation of a loop in the lagging strand of the replication fork to reorient the lagging-strand DNA polymerase so that it advances in parallel with the leading-strand polymerase. The replication loop grows and shrinks during each cycle of Okazaki fragment synthesis. Here we use single-molecule techniques to visualize, in real time, the formation and release of replication loops by individual replisomes of bacteriophage T7 supporting coordinated DNA replication. Analysis of the distributions of loop sizes and lag times between loops reveals that initiation of primer synthesis and the completion of an Okazaki fragment each serve as a trigger for loop release. The presence of two triggers may represent a fail-safe mechanism ensuring the timely reset of the replisome after the synthesis of every Okazaki fragment.
CH radio emission from heiles cloud 2 as a tracer of molecular cloud evolution
A mapping observation of the -type doubling transition (3.3
GHz) of CH has been conducted toward Heiles Cloud 2 (HCL2) in the Taurus
molecular cloud complex to reveal its molecular cloud-scale distribution. The
observations were carried out with the Effelsberg 100 m telescope. The CH
emission is found to be extended over the whole region of HCL2. It is brighter
in the southeastern part, which encloses the TMC-1 cyanopolyyne peak than in
the northwestern part. Its distribution extends continuously from the peak of
the neutral carbon emission (CI peak) to the TMC-1 ridge, as if it were
connecting the distributions of the [C I] and CO emissions. Since CH is
an intermediate in gas-phase chemical reactions from C to CO, its emission
should trace the transition region. The above distribution of the CH emission
is consistent with this chemical behavior. Since the CH abundance is subject to
the chemical evolutionary effect, the CH column density in HCL2 no longer
follows a linear correlation wit the H column density reported for diffuse
and translucent clouds. More importantly, the CH line profile is found to be
composed of the narrow and broad components. Although the broad component is
dominant around the CI peak, the narrow component appears in the TMC-1 ridge
and dense core regions such as L1527 and TMC-1A. This trend seems to reflect a
narrowing of the line width during the formation of dense cores. These results
suggest that the 3.3 GHz CH line is a useful tool for tracing the chemical and
physical evolution of molecular clouds.Comment: 8 page
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Connecting research and practice in TESOL: a community of practice perspective
In line with a growing interest in teacher research engagement in second language education, this article is an attempt to shed light on teachers’ views on the relationship between teaching and practice. The data comprise semi-structured interviews with 20 teachers in England, examining their views about the divide between research and practice in their field, the reasons for the persistence of the divide between the two and their suggestions on how to bridge it. Wenger’s (1998) Community of Practice (CoP) is used as a conceptual framework to analyse and interpret the data. The analysis indicates that teacher experience, learning and ownership of knowledge emerging from participation in their CoP are key players in teachers’ professional practice and in the development of teacher identity. The participants construe the divide in the light of the differences they perceive between teaching and research as two different CoPs, and attribute the divide to the limited mutual engagement, absence of a joint enterprise and lack of a shared repertoire between them. Boundary encounters, institutionalised brokering and a more research-oriented teacher education provision are some of the suggestions for bringing the two communities together
Titanium dioxide nanoparticles activate the ATM-Chk2 DNA damage response in human dermal fibroblasts
The use of nanoparticles in consumer products increases their prevalence in the environment and the potential risk to human health. Although recent studies have shown in vivo and in vitro toxicity of titanium dioxide nanoparticles (nano-TiO2), a more detailed view of the underlying mechanisms of this response needs to be established. Here the effects of nano-TiO2 on the DNA damage response and DNA replication dynamics were investigated in human dermal fibroblasts. Specifically, the relationship between nano-TiO2 and the DNA damage response pathways regulated by ATM/Chk2 and ATR/Chk1 were examined. The results show increased phosphorylation of H2AX, ATM, and Chk2 after exposure. In addition, nano-TiO2 inhibited the overall rate of DNA synthesis and frequency of replicon initiation events in DNA combed fibers. Taken together, these results demonstrate that exposure to nano-TiO2 activates the ATM/Chk2 DNA damage response pathway
Carbon States in Carbon-Encapsulated Nickel Nanoparticles Studied by Means of X-Ray Absorption, Emission, and Photoelectron Spectroscopies
Electronic structure of nickel nanoparticles encapsulated in carbon was
characterized by photoelectron, X-ray absorption, and X-ray emission
spectroscopies. Experimental spectra are compared with the density of states
calculated in the frame of the density functional theory. The carbon shell of
Ni nanoparticles has been found to be multilayer graphene with significant
(about 6%) amount of Stone--Wales defects. Results of the experiments evidence
protection of the metallic nanoparticles from the environmental degradation by
providing a barrier against oxidation at least for two years. Exposure in air
for 2 years leads to oxidation only of the carbon shell of Ni@C nanoparticles
with coverage of functional groups.Comment: 16 pages, 6 figures, accepted in J. Phys. Chem.
Effective intra-S checkpoint responses to UVC in primary human melanocytes and melanoma cell lines
The objective of this study was to assess potential functional attenuation or inactivation of the intra-S checkpoint during melanoma development. Proliferating cultures of skin melanocytes, fibroblasts and melanoma cell lines were exposed to increasing fluences of UVC and intra-S checkpoint responses were quantified. Melanocytes displayed stereotypic intra-S checkpoint responses to UVC qualitatively and quantitatively equivalent to those previously demonstrated in skin fibroblasts. In comparison to fibroblasts, primary melanocytes displayed reduced UVC-induced inhibition of DNA strand growth and enhanced degradation of p21Waf1 after UVC, suggestive of enhanced bypass of UVC-induced DNA photoproducts. All nine melanoma cell lines examined, including those with activating mutations in BRAF or and NRAS oncogenes, also displayed proficiency in activation of the intra-S checkpoint in response to UVC irradiation. The results indicate that bypass of oncogene-induced senescence during melanoma development was not associated with inactivation of the intra-S checkpoint response to UVC-induced DNA replication stress
A Baker\u27s Dozen of Top Antimicrobial Stewardship Intervention Publications in 2018
© The Author(s) 2019 Phytochemical investigation of methanolic extract of Limonium leptophyllum (Plumbaginaceae), led to the isolation of 1 new isoflavonoid with a rare 5-membered dihydrofuran ring (1, leptoisoflavone A) and 8 known compounds. The known isolated compounds were identified as euchrenone b9 (2), auriculasin (3), kaempferol (4), avicularoside (5), myrice-tin-3-arabinoside (6), trans-N-feruloyltyramine (7), trans-N-caffeoyltyramine (8), and β-sitosterol (9). The crude methanolic extract exhibited moderate activity toward endocannabinoid receptors. Auriculasin (3) showed activity toward cannabinoid receptor type 1 (86.7% displacement with IC50 8.92 μM)
Herschel/HIFI observations of spectrally resolved methylidyne signatures toward the high-mass star-forming core NGC6334I
In contrast to extensively studied dense star-forming cores, little is known
about diffuse gas surrounding star-forming regions. We study molecular gas in
the high-mass star-forming region NGC6334I, which contains diffuse, quiescent
components that are inconspicuous in widely used molecular tracers such as CO.
We present Herschel/HIFI observations of CH toward NGC6334I observed as part of
the CHESS key program. HIFI resolves the hyperfine components of its J=3/2-1/2
transition, observed in both emission and absorption. The CH emission appears
close to the systemic velocity of NGC6334I, while its measured linewidth of 3
km/s is smaller than previously observed in dense gas tracers such as NH3 and
SiO. The CH abundance in the hot core is 7 10^-11, two to three orders of
magnitude lower than in diffuse clouds. While other studies find distinct
outflows in, e.g., CO and H2O toward NGC6334I, we do not detect outflow
signatures in CH. To explain the absorption signatures, at least two absorbing
components are needed at -3.0 and +6.5 km/s with N(CH)=7 10^13 and 3 10^13
cm^-2. Two additional absorbing clouds are found at +8.0 and 0.0 km/s, both
with N(CH)=2 10^13 cm^-2. Turbulent linewidths for the four absorption
components vary between 1.5 and 5.0 km/s in FWHM. We constrain physical
properties of our CH clouds by matching our CH absorbers with other absorption
signatures. In the hot core, molecules such as H2O and CO trace gas that is
heated and dynamically influenced by outflow activity, whereas CH traces more
quiescent material. The four CH absorbers have column densities and turbulent
properties consistent with diffuse clouds: two are located near NGC6334, and
two are unrelated foreground clouds. Local density and dynamical effects
influence the chemical composition of physical components of NGC6334, causing
some components to be seen in CH but not in other tracers, and vice versa.Comment: Accepted by A&A Letters; 5 pages, 1 figure; v2: minor textual and
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