4,168 research outputs found
Dichotomous development of the gut microbiome in preterm infants.
BackgroundPreterm infants are at risk of developing intestinal dysbiosis with an increased proportion of Gammaproteobacteria. In this study, we sought the clinical determinants of the relative abundance of feces-associated Gammaproteobacteria in very low birth weight (VLBW) infants. Fecal microbiome was characterized at ≤ 2 weeks and during the 3rd and 4th weeks after birth, by 16S rRNA amplicon sequencing. Maternal and infant clinical characteristics were extracted from electronic medical records. Data were analyzed by linear mixed modeling and linear regression.ResultsClinical data and fecal microbiome profiles of 45 VLBW infants (gestational age 27.9 ± 2.2 weeks; birth weight 1126 ± 208 g) were studied. Three stool samples were analyzed for each infant at mean postnatal ages of 9.9 ± 3, 20.7 ± 4.1, and 29.4 ± 4.9 days. The average relative abundance of Gammaproteobacteria was 42.5% (0-90%) at ≤ 2 weeks, 69.7% (29.9-86.9%) in the 3rd, and 75.5% (54.5-86%) in the 4th week (p < 0.001). Hierarchical and K-means clustering identified two distinct subgroups: cluster 1 started with comparatively low abundance that increased with time, whereas cluster 2 began with a greater abundance at ≤ 2 weeks (p < 0.001) that decreased over time. Both groups resembled each other by the 3rd week. Single variants of Klebsiella and Staphylococcus described variance in community structure between clusters and were shared between all infants, suggesting a common, hospital-derived source. Fecal Gammaproteobacteria was positively associated with vaginal delivery and antenatal steroids.ConclusionsWe detected a dichotomy in gut microbiome assembly in preterm infants: some preterm infants started with low relative gammaproteobacterial abundance in stool that increased as a function of postnatal age, whereas others began with and maintained high abundance. Vaginal birth and antenatal steroids were identified as predictors of Gammaproteobacteria abundance in the early (≤ 2 weeks) and later (3rd and 4th weeks) stool samples, respectively. These findings are important in understanding the development of the gut microbiome in premature infants
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Investigating the Impact of Storage Conditions on Microbial Community Composition in Soil Samples
Recent advances in DNA sequencing technologies have allowed scientists to probe increasingly complex biological systems, including the diversity of bacteria in the environment. However, despite a multitude of recent studies incorporating these methods, many questions regarding how environmental samples should be collected and stored still persist. Here, we assess the impact of different soil storage conditions on microbial community composition using Illumina-based 16S rRNA V4 amplicon sequencing. Both storage time and temperature affected bacterial community composition and structure. Frozen samples maintained the highest alpha diversity and differed least in beta diversity, suggesting the utility of cold storage for maintaining consistent communities. Samples stored for intermediate times (three and seven days) had both the highest alpha diversity and the largest differences in overall beta diversity, showing the degree of community change after sample collection. These divergences notwithstanding, differences in neither storage time nor storage temperature substantially altered overall communities relative to more than 500 previously examined soil samples. These results systematically support previous studies and stress the importance of methodological consistency for accurate characterization and comparison of soil microbiological assemblages.</p
SEARCH: Spatially Explicit Animal Response to Composition of Habitat.
Complex decisions dramatically affect animal dispersal and space use. Dispersing individuals respond to a combination of fine-scale environmental stimuli and internal attributes. Individual-based modeling offers a valuable approach for the investigation of such interactions because it combines the heterogeneity of animal behaviors with spatial detail. Most individual-based models (IBMs), however, vastly oversimplify animal behavior and such behavioral minimalism diminishes the value of these models. We present program SEARCH (Spatially Explicit Animal Response to Composition of Habitat), a spatially explicit, individual-based, population model of animal dispersal through realistic landscapes. SEARCH uses values in Geographic Information System (GIS) maps to apply rules that animals follow during dispersal, thus allowing virtual animals to respond to fine-scale features of the landscape and maintain a detailed memory of areas sensed during movement. SEARCH also incorporates temporally dynamic landscapes so that the environment to which virtual animals respond can change during the course of a simulation. Animals in SEARCH are behaviorally dynamic and able to respond to stimuli based upon their individual experiences. Therefore, SEARCH is able to model behavioral traits of dispersing animals at fine scales and with many dynamic aspects. Such added complexity allows investigation of unique ecological questions. To illustrate SEARCH\u27s capabilities, we simulated case studies using three mammals. We examined the impact of seasonally variable food resources on the weight distribution of dispersing raccoons (Procyon lotor), the effect of temporally dynamic mortality pressure in combination with various levels of behavioral responsiveness in eastern chipmunks (Tamias striatus), and the impact of behavioral plasticity and home range selection on disperser mortality and weight change in virtual American martens (Martes americana). These simulations highlight the relevance of SEARCH for a variety of applications and illustrate benefits it can provide for conservation planning
The SPLASH Survey: Kinematics of Andromeda's Inner Spheroid
The combination of large size, high stellar density, high metallicity, and
Sersic surface brightness profile of the spheroidal component of the Andromeda
galaxy (M31) within R_proj ~ 20 kpc suggest that it is unlike any subcomponent
of the Milky Way. In this work we capitalize on our proximity to and external
view of M31 to probe the kinematical properties of this "inner spheroid." We
employ a Markov chain Monte Carlo (MCMC) analysis of resolved stellar
kinematics from Keck/DEIMOS spectra of 5651 red giant branch stars to
disentangle M31's inner spheroid from its stellar disk. We measure the mean
velocity and dispersion of the spheroid in each of five spatial bins after
accounting for a locally cold stellar disk as well as the Giant Southern Stream
and associated tidal debris. For the first time, we detect significant spheroid
rotation (v_rot ~ 50 km/s) beyond R_proj ~ 5 kpc. The velocity dispersion
decreases from about 140 km/s at R_proj = 7 kpc to 120 km/s at R_proj = 14 kpc,
consistent to 2 sigma with existing measurements and models. We calculate the
probability that a given star is a member of the spheroid and find that the
spheroid has a significant presence throughout the spatial extent of our
sample. Lastly, we show that the flattening of the spheroid is due to velocity
anisotropy in addition to rotation. Though this suggests that the inner
spheroid of M31 more closely resembles an elliptical galaxy than a typical
spiral galaxy bulge, it should be cautioned that our measurements are much
farther out (2 - 14 r_eff) than for the comparison samples.Comment: Accepted for publication in Ap
DNA extraction protocols cause differences in 16S rRNA amplicon sequencing efficiency but not in community profile composition or structure
The recent development of methods applying next-generation sequencing to microbial community characterization has led to the proliferation of these studies in a wide variety of sample types. Yet, variation in the physical properties of environmental samples demands that optimal DNA extraction techniques be explored for each new environment. The microbiota associated with many species of insects offer an extraction challenge as they are frequently surrounded by an armored exoskeleton, inhibiting disruption of the tissues within. In this study, we examine the efficacy of several commonly used protocols for extracting bacterial DNA from ants. While bacterial community composition recovered using Illumina 16S rRNA amplicon sequencing was not detectably biased by any method, the quantity of bacterial DNA varied drastically, reducing the number of samples that could be amplified and sequenced. These results indicate that the concentration necessary for dependable sequencing is around 10,000 copies of target DNA per microliter. Exoskeletal pulverization and tissue digestion increased the reliability of extractions, suggesting that these steps should be included in any study of insect-associated microorganisms that relies on obtaining microbial DNA from intact body segments. Although laboratory and analysis techniques should be standardized across diverse sample types as much as possible, minimal modifications such as these will increase the number of environments in which bacterial communities can be successfully studied
Dynamics of chromosome organization in a minimal bacterial cell
Computational models of cells cannot be considered complete unless they include the most fundamental process of life, the replication and inheritance of genetic material. By creating a computational framework to model systems of replicating bacterial chromosomes as polymers at 10 bp resolution with Brownian dynamics, we investigate changes in chromosome organization during replication and extend the applicability of an existing whole-cell model (WCM) for a genetically minimal bacterium, JCVI-syn3A, to the entire cell-cycle. To achieve cell-scale chromosome structures that are realistic, we model the chromosome as a self-avoiding homopolymer with bending and torsional stiffnesses that capture the essential mechanical properties of dsDNA in Syn3A. In addition, the conformations of the circular DNA must avoid overlapping with ribosomes identitied in cryo-electron tomograms. While Syn3A lacks the complex regulatory systems known to orchestrate chromosome segregation in other bacteria, its minimized genome retains essential loop-extruding structural maintenance of chromosomes (SMC) protein complexes (SMC-scpAB) and topoisomerases. Through implementing the effects of these proteins in our simulations of replicating chromosomes, we find that they alone are sufficient for simultaneous chromosome segregation across all generations within nested theta structures. This supports previous studies suggesting loop-extrusion serves as a near-universal mechanism for chromosome organization within bacterial and eukaryotic cells. Furthermore, we analyze ribosome diffusion under the influence of the chromosome and calculate in silico chromosome contact maps that capture inter-daughter interactions. Finally, we present a methodology to map the polymer model of the chromosome to a Martini coarse-grained representation to prepare molecular dynamics models of entire Syn3A cells, which serves as an ultimate means of validation for cell states predicted by the WCM. </p
Composition Structure of Interplanetary Coronal Mass Ejections From Multispacecraft Observations, Modeling, and Comparison with Numerical Simulations
We present an analysis of the ionic composition of iron for two
interplanetary coronal mass ejections observed in May 21-23 2007 by the ACE and
STEREO spacecraft in the context of the magnetic structure of the ejecta flux
rope, sheath region, and surrounding solar wind flow. This analysis is made
possible due to recent advances in multispacecraft data interpolation,
reconstruction, and visualization as well as results from recent modeling of
ionic charge states in MHD simulations of magnetic breakout and flux
cancellation CME initiation. We use these advances to interpret specific
features of the ICME plasma composition resulting from the magnetic topology
and evolution of the CME. We find that in both the data and our MHD
simulations, the flux ropes centers are relatively cool, while charge state
enhancements surround and trail the flux ropes. The magnetic orientation of the
ICMEs are suggestive of magnetic breakout-like reconnection during the eruption
process, which could explain the spatial location of the observed iron
enhancements just outside the traditional flux rope magnetic signatures and
between the two ICMEs. Detailed comparisons between the simulations and data
were more complicated, but a sharp increase in high iron charge states in the
ACE and STEREO-A data during the second flux rope corresponds well to similar
features in the flux cancellation results. We discuss the prospects of this
integrated in-situ data analysis and modeling approach to advancing our
understanding of the unified CME-to-ICME evolution.Comment: Accepted for submission to The Astrophysical Journa
The Kepler Smear Campaign: Light curves for 102 Very Bright Stars
We present the first data release of the Kepler Smear Campaign, using
collateral 'smear' data obtained in the Kepler four-year mission to reconstruct
light curves of 102 stars too bright to have been otherwise targeted. We
describe the pipeline developed to extract and calibrate these light curves,
and show that we attain photometric precision comparable to stars analyzed by
the standard pipeline in the nominal Kepler mission. In this paper, aside from
publishing the light curves of these stars, we focus on 66 red giants for which
we detect solar-like oscillations, characterizing 33 of these in detail with
spectroscopic chemical abundances and asteroseismic masses as benchmark stars.
We also classify the whole sample, finding nearly all to be variable, with
classical pulsations and binary effects. All source code, light curves, TRES
spectra, and asteroseismic and stellar parameters are publicly available as a
Kepler legacy sample.Comment: 35 pages, accepted ApJ
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