219 research outputs found
Antagonistic effect of probiotic strains against two pathogens: Salmonella Typhimurium and E. coli O157:H7
El objetivo de este estudio fue probar la eficiencia de las cepas probióticas Lactobacillus acidophilus NCFM (L. acidophilus), Lactobacillus rhamnosus HN001 (L. rhmanosus) y Bifidobacterium animalis BI07 (B. animalis) para antagonizar los patógenos resistentes a antibióticos Salmonella enteritidis var Thyphimurium (Salmonella Thyphimurium) y Escherichia coli O157:H7 (E. coli O157:H7). Las tres cepas probióticas mostraron poseer un efecto antagónico contra las cepas patógenas Salmonella Thyphimurium y E. coli O157:H7 resistentes a antibióticos. En la prueba de “Well Diffusion”, L. acidophilus y L. rhamnosus presentaron reducciones estadísticamente semejantes entre ellas (P >0.05) de 37-41 mm para E. coli O157:H7 y de 32 – 41 mm para Salmonella Thyphimurium, mientras que B. animalis mostró reducciones menores (P0.05).Consejo Nacional de Ciencia y TecnologíaGastronómica La Buena MesaJabil Circuit GuadalajaraKurago BiotekUniversidad de Guadalajar
The X-ray puzzle of the L1551 IRS 5 jet
Protostars are actively accreting matter and they drive spectacular, dynamic
outflows, which evolve on timescales of years. X-ray emission from these jets
has been detected only in a few cases and little is known about its time
evolution. We present a new Chandra observation of L1551 IRS 5's jet in the
context of all available X-ray data of this object. Specifically, we perform a
spatially resolved spectral analysis of the X-ray emission and find that (a)
the total X-ray luminosity is constant over almost one decade, (b) the majority
of the X-rays appear to be always located close to the driving source, (c)
there is a clear trend in the photon energy as a function of the distance to
the driving source indicating that the plasma is cooler at larger distances and
(d) the X-ray emission is located in a small volume which is unresolved
perpendicular to the jet axis by Chandra. A comparison of our X-ray data of the
L1551 IRS 5 jet both with models as well as X-ray observations of other
protostellar jets shows that a base/standing shock is a likely and plausible
explanation for the apparent constancy of the observed X-ray emission. Internal
shocks are also consistent with the observed morphology if the supply of jet
material by the ejection of new blobs is sufficiently constant. We conclude
that the study of the X-ray emission of protostellar jet sources allows us to
diagnose the innermost regions close to the acceleration region of the
outflows.Comment: A&A accepted, 14 pages, 9 figure
Molecular evolution of the membrane associated progesterone receptor in the Brachionus plicatilis (Rotifera, Monogononta) species complex
Author Posting. © Springer, 2010. This is the author's version of the work. It is posted here by permission of Springer for personal use, not for redistribution. The definitive version was published in Hydrobiologia 662 (2011): 99-106, doi:10.1007/s10750-010-0484-4.Many studies have investigated physiological roles of the membrane associated progesterone
receptor (MAPR), but little is known of its evolution. Marked variations in response to
exogenous progesterone have been reported for four brachionid rotifer species, suggesting
differences in progesterone signaling and reception. Here we report sequence variation for the
MAPR gene in the Brachionus plicatilis species complex. Phylogenetic analysis of this receptor
is compared with relatedness based on cytochrome c oxidase subunit 1 sequences.
Nonsynonymous to synonymous site substitution rate ratios, amino acid divergence, and
variations in predicted phosphorylation sites are examined to assess evolution of the MAPR
among brachionid clades.National Science Foundation grant BE/GenEn MCB-0412674E to TWS and DMW, and an NSF
IGERT fellowship to HAS under DGE 0114400, supported this work
Molecular Outflows Identified in the FCRAO CO Survey of the Taurus Molecular Cloud
The 100 square degree FCRAO CO survey of the Taurus molecular cloud provides
an excellent opportunity to undertake an unbiased survey of a large, nearby,
molecular cloud complex for molecular outflow activity. Our study provides
information on the extent, energetics and frequency of outflows in this region,
which are then used to assess the impact of outflows on the parent molecular
cloud. The search identified 20 outflows in the Taurus region, 8 of which were
previously unknown. Both CO and CO data cubes from the Taurus
molecular map were used, and dynamical properties of the outflows are derived.
Even for previously known outflows, our large-scale maps indicate that many of
the outflows are much larger than previously suspected, with eight of the flows
(40%) being more than a parsec long. The mass, momentum and kinetic energy from
the 20 outflows are compared to the repository of turbulent energy in Taurus.
Comparing the energy deposition rate from outflows to the dissipation rate of
turbulence, we conclude that outflows by themselves cannot sustain the observed
turbulence seen in the entire cloud. However, when the impact of outflows is
studied in selected regions of Taurus, it is seen that locally, outflows can
provide a significant source of turbulence and feedback. Five of the eight
newly discovered outflows have no known associated stellar source, indicating
that they may be embedded Class 0 sources. In Taurus, 30% of Class I sources
and 12% of Flat spectrum sources from the Spitzer YSO catalogue have outflows,
while 75% of known Class 0 objects have outflows. Overall, the paucity of
outflows in Taurus compared to the embedded population of Class I and Flat
Spectrum YSOs indicate that molecular outflows are a short-lived stage marking
the youngest phase of protostellar life.Comment: Accepted for publication in MNRAS; 28 pages, 60 figures, 5 tables.
For full abstract, see pape
The young stellar population in the Serpens Cloud Core: An ISOCAM survey
We present results from an ISOCAM survey in the two broad band filters LW2
(5-8.5 mu) and LW3 (12-18 mu) of a 0.13 square degree coverage of the Serpens
Main Cloud Core. A total of 392 sources were detected in the 6.7 mu band and
139 in the 14.3 mu band to a limiting sensitivity of ~ 2 mJy. Only about 50% of
the mid-IR excess sources show excesses in the near-IR J-H/H-K diagram. In the
central Cloud Core the Class I/Class II number ratio is 19/18, i.e. about 10
times larger than in other young embedded clusters such as rho Ophiuchi or
Chamaeleon. The mid-IR fluxes of the Class I and flat-spectrum sources are
found to be on the average larger than those of Class II sources. Stellar
luminosities are estimated for the Class II sample, and its luminosity function
is compatible with a coeval population of about 2 Myr which follows a three
segment power-law IMF. For this age about 20% of the Class IIs are found to be
young brown dwarf candidates. The YSOs are in general strongly clustered, the
Class I sources more than the Class II sources, and there is an indication of
sub-clustering. The sub-clustering of the protostar candidates has a spatial
scale of 0.12 pc. These sub-clusters are found along the NW-SE oriented ridge
and in very good agreement with the location of dense cores traced by
millimeter data. The smallest clustering scale for the Class II sources is
about 0.25 pc, similar to what was found for rho Ophiuchi. Our data show
evidence that star formation in Serpens has proceeded in several phases, and
that a ``microburst'' of star formation has taken place very recently, probably
within the last 10^5 yrs.Comment: 25 pages, 14 figures, accepted by A&A March 18th, see also
http://www.not.iac.es/~amanda
Identification of Methanoculleus spp. as active methanogens during anoxic incubations of swine manure storage tank samples
Methane emissions represent a major environmental concern associated with manure management in the livestock industry. A more thorough understanding of how microbial communities function in manure storage tanks is a prerequisite for mitigating methane emissions. Identifying the microorganisms that are metabolically active is an important first step. Methanogenic archaea are major contributors to methanogenesis in stored swine manure, and we investigated active methanogenic populations by DNA stable isotope probing (DNA-SIP). Following a preincubation of manure samples under anoxic conditions to induce substrate starvation, [U-¹³C] acetate was added as a labeled substrate. Fingerprint analysis of density-fractionated DNA, using length-heterogeneity analysis of PCR-amplified mcrA genes (encoding the alpha subunit of methyl coenzyme M reductase), showed that the incorporation of ¹³C into DNA was detectable at in situ acetate concentrations (~7g/liter). Fingerprints of DNA retrieved from heavy fractions of the ¹³C treatment were primarily enriched in a 483-bp amplicon and, to a lesser extent, in a 481-bp amplicon. Analyses based on clone libraries of the mcrA and 16S rRNA genes revealed that both of these heavy DNA amplicons corresponded to Methanoculleus spp. Our results demonstrate that uncultivated methanogenic archaea related to Methanoculleus spp. were major contributors to acetate-C assimilation during the anoxic incubation of swine manure storage tank samples. Carbon assimilation and dissimilation rate estimations suggested that Methanoculleus spp. were also major contributors to methane emissions and that the hydrogenotrophic pathway predominated during methanogenesis
Counteracting Quasispecies Adaptability: Extinction of a Ribavirin-Resistant Virus Mutant by an Alternative Mutagenic Treatment
[Background] Lethal mutagenesis, or virus extinction promoted by mutagen-induced elevation of mutation rates of viruses,
may meet with the problem of selection of mutagen-resistant variants, as extensively documented for standard, nonmutagenic
antiviral inhibitors. Previously, we characterized a mutant of foot-and-mouth disease virus that included in its
RNA-dependent RNA polymerase replacement M296I that decreased the sensitivity of the virus to the mutagenic nucleoside
analogue ribavirin.[Methodology and Principal Findings] Replacement M296I in the viral polymerase impedes the extinction of the mutant
foot-and-mouth disease virus by elevated concentrations of ribavirin. In contrast, wild type virus was extinguished by the
same ribavirin treatment and, interestingly, no mutants resistant to ribavirin were selected from the wild type populations.
Decreases of infectivity and viral load of the ribavirin-resistant M296I mutant were attained with a combination of the
mutagen 5-fluorouracil and the non-mutagenic inhibitor guanidine hydrocloride. However, extinction was achieved with a
sequential treatment, first with ribavirin, and then with a minimal dose of 5-fluorouracil in combination with guanidine
hydrochloride. Both, wild type and ribavirin-resistant mutant M296I exhibited equal sensitivity to this combination,
indicating that replacement M296I in the polymerase did not confer a significant cross-resistance to 5-fluorouracil. We
discuss these results in relation to antiviral designs based on lethal mutagenesis[Conclusions] (i) When dominant in the population, a mutation that confers partial resistance to a mutagenic agent can
jeopardize virus extinction by elevated doses of the same mutagen. (ii) A wild type virus, subjected to identical high
mutagenic treatment, need not select a mutagen-resistant variant, and the population can be extinguished. (iii) Extinction
of the mutagen-resistant variant can be achieved by a sequential treatment of a high dose of the same mutagen, followed
by a combination of another mutagen with an antiviral inhibitor.Work supported by grants BFU2005-00863, BFU2008-02816/BMC, Proyecto Intramural de Frontera del CSIC 200820FO191, FIPSE 36558/06, and
Fundacio´n Ramo´n Areces. CIBERehd is funded by Instituto de Salud Carlos III. The funders had no role in study design, data collection and analysis, decision to
publish, or preparation of the manuscriptPeer reviewe
Highly variable microbiota development in the chicken gastrointestinal tract
Studies investigating the role that complex microbiotas associated with animals and humans play in health and wellbeing have been greatly facilitated by advances in DNA sequencing technology. Due to the still relatively high sequencing costs and the expense of establishing and running animal trials and collecting clinical samples, most of the studies reported in the literature are limited to a single trial and relatively small numbers of samples. Results from different laboratories, investigating similar trials and samples, have often produced quite different pictures of microbiota composition. This study investigated batch to batch variations in chicken cecal microbiota across three similar trials, represented by individually analysed samples from 207 birds. Very different microbiota profiles were found across the three flocks. The flocks also differed in the efficiency of nutrient use as indicated by feed conversion ratios. In addition, large variations in the microbiota of birds within a single trial were noted. It is postulated that the large variability in microbiota composition is due, at least in part, to the lack of colonisation of the chicks by maternally derived bacteria. The high hygiene levels maintained in modern commercial hatcheries, although effective in reducing the burden of specific diseases, may have the undesirable effect of causing highly variable bacterial colonization of the gut. Studies in humans and other animals have previously demonstrated large variations in microbiota composition when comparing individuals from different populations and from different environments but this study shows that even under carefully controlled conditions large variations in microbiota composition still occur.Dragana Stanley, Mark S. Geier, Robert J. Hughes, Stuart E. Denman and Robert J. Moor
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