The Extracellular Matrix of Staphylococcus aureus Biofilms Comprises Cytoplasmic Proteins That Associate with the Cell Surface in Response to Decreasing pH

ABSTRACT Biofilm formation by Staphylococcus aureus involves the formation of an extracellular matrix, but the composition of this matrix has been uncertain. Here we report that the matrix is largely composed of cytoplasmic proteins that reversibly associate with the cell surface in a manner that depends on pH. We propose a model for biofilm formation in which cytoplasmic proteins are released from cells in stationary phase. These proteins associate with the cell surface in response to decreasing pH during biofilm formation. Rather than utilizing a dedicated matrix protein, S. aureus appears to recycle cytoplasmic proteins that moonlight as components of the extracellular matrix

Environmental gradients and the evolution of successional habitat specialization: A test case with 14 Neotropical forest sites

© 2015 British Ecological Society. Successional gradients are ubiquitous in nature, yet few studies have systematically examined the evolutionary origins of taxa that specialize at different successional stages. Here we quantify successional habitat specialization in Neotropical forest trees and evaluate its evolutionary lability along a precipitation gradient. Theoretically, successional habitat specialization should be more evolutionarily conserved in wet forests than in dry forests due to more extreme microenvironmental differentiation between early and late-successional stages in wet forest. We applied a robust multinomial classification model to samples of primary and secondary forest trees from 14 Neotropical lowland forest sites spanning a precipitation gradient from 788 to 4000 mm annual rainfall, identifying species that are old-growth specialists and secondary forest specialists in each site. We constructed phylogenies for the classified taxa at each site and for the entire set of classified taxa and tested whether successional habitat specialization is phylogenetically conserved. We further investigated differences in the functional traits of species specializing in secondary vs. old-growth forest along the precipitation gradient, expecting different trait associations with secondary forest specialists in wet vs. dry forests since water availability is more limiting in dry forests and light availability more limiting in wet forests. Successional habitat specialization is non-randomly distributed in the angiosperm phylogeny, with a tendency towards phylogenetic conservatism overall and a trend towards stronger conservatism in wet forests than in dry forests. However, the specialists come from all the major branches of the angiosperm phylogeny, and very few functional traits showed any consistent relationships with successional habitat specialization in either wet or dry forests. Synthesis. The niche conservatism evident in the habitat specialization of Neotropical trees suggests a role for radiation into different successional habitats in the evolution of species-rich genera, though the diversity of functional traits that lead to success in different successional habitats complicates analyses at the community scale. Examining the distribution of particular lineages with respect to successional gradients may provide more insight into the role of successional habitat specialization in the evolution of species-rich taxa

Environmental gradients and the evolution of successional habitat specialization: A test case with 14 Neotropical forest sites

https://www.scopus.com/inward/record.url?eid=2-s2.0-84939570316&partnerID=40&md5=fcadae8e6c274e8b7efca96099304a7cSuccessional gradients are ubiquitous in nature, yet few studies have systematically examined the evolutionary origins of taxa that specialize at different successional stages. Here we quantify successional habitat specialization in Neotropical forest trees and evaluate its evolutionary lability along a precipitation gradient. Theoretically, successional habitat specialization should be more evolutionarily conserved in wet forests than in dry forests due to more extreme microenvironmental differentiation between early and late-successional stages in wet forest. We applied a robust multinomial classification model to samples of primary and secondary forest trees from 14 Neotropical lowland forest sites spanning a precipitation gradient from 788 to 4000 mm annual rainfall, identifying species that are old-growth specialists and secondary forest specialists in each site. We constructed phylogenies for the classified taxa at each site and for the entire set of classified taxa and tested whether successional habitat specialization is phylogenetically conserved. We further investigated differences in the functional traits of species specializing in secondary vs. old-growth forest along the precipitation gradient, expecting different trait associations with secondary forest specialists in wet vs. dry forests since water availability is more limiting in dry forests and light availability more limiting in wet forests. Successional habitat specialization is non-randomly distributed in the angiosperm phylogeny, with a tendency towards phylogenetic conservatism overall and a trend towards stronger conservatism in wet forests than in dry forests. However, the specialists come from all the major branches of the angiosperm phylogeny, and very few functional traits showed any consistent relationships with successional habitat specialization in either wet or dry forests. Synthesis. The niche conservatism evident in the habitat specialization of Neotropical trees suggests a role for radiation into different successional habitats in the evolution of species-rich genera, though the diversity of functional traits that lead to success in different successional habitats complicates analyses at the community scale. Examining the distribution of particular lineages with respect to successional gradients may provide more insight into the role of successional habitat specialization in the evolution of species-rich taxa

MRI evidence: acute mountain sickness is not associated with cerebral edema formation during simulated high altitude.

Acute mountain sickness (AMS) is a common condition among non-acclimatized individuals ascending to high altitude. However, the underlying mechanisms causing the symptoms of AMS are still unknown. It has been suggested that AMS is a mild form of high-altitude cerebral edema both sharing a common pathophysiological mechanism. We hypothesized that brain swelling and consequently AMS development is more pronounced when subjects exercise in hypoxia compared to resting conditions. Twenty males were studied before and after an eight hour passive (PHE) and active (plus exercise) hypoxic exposure (AHE) (F(i)O(2) = 11.0%, P(i)O(2)∼80 mmHg). Cerebral edema formation was investigated with a 1.5 Tesla magnetic resonance scanner and analyzed by voxel based morphometry (VBM), AMS was assessed using the Lake Louise Score. During PHE and AHE AMS was diagnosed in 50% and 70% of participants, respectively (p>0.05). While PHE slightly increased gray and white matter volume and the apparent diffusion coefficient, these changes were clearly more pronounced during AHE but were unrelated to AMS. In conclusion, our findings indicate that rest and especially exercise in normobaric hypoxia are associated with accumulation of water in the extracellular space, however independent of AMS development. Thus, it is suggested that AMS and HACE do not share a common pathophysiological mechanism

Oxygen saturation (SpO₂) in %, heart rate (HR) in beats per min, systolic (Sys. Bp) and diastolic (Dia. Bp) blood pressure in mmHg of baseline measurements and during hypoxia.

<p>BL_PHE and BL_AHE: Baseline measurements of the passive hypoxic exposure (PHE) and the active hypoxic exposure (AHE) of the whole group, Hypoxia_PHE and Hypoxia_AHE: measurements during PHE and AHE (average of H2–H8) of the whole group. AMS+ and AMS−: subject with and without AMS. p^a: difference between BL_PHE and Hypoxia_PHE respectively BL_AHE and Hypoxia_AHE, p^b: difference between AMS− and AMS+ subjects during PHE respectively AHE. Values are expressed as means ± standard deviation.</p

Characteristics of all study participants and separated for subjects with (AMS+) and without AMS (AMS−) during the passive (PHE) and active hypoxic exposure (AHE).

<p>p^a and p^b: differences between AMS− and AMS+ subjects during PHE and AHE, respectively. Data are expressed as means ± standard deviation (range) or as frequencies.</p

Regional cerebral changes during the passive hypoxic exposure (PHE) for the entire group (N = 20).

<p>Areas with significant increases of gray (GM) and white matter (WM) volume are presented in yellow, ADC increases are presented in red (p<0.001, uncorrected). Right hemisphere in the figure denotes left hemisphere of the brain and vice versa. A general T₁ image provided by xjView 8 was used as background.</p

Anatomical regions with significant increases of apparent diffusion coefficient (ADC) during the active hypoxic exposure (AHE) (p<0.001, uncorrected).

<p>Gray matter (GM), white matter (WM), Left (L), Right (R), coordinates (x, y, z) are given in Montreal Neurological Institute (MNI) space showing the center of each cluster.</p

Anatomical regions with significant increases of apparent diffusion coefficient (ADC) during the passive hypoxic exposure (PHE) (p<0.001, uncorrected).

<p>Gray matter (GM), white matter (WM), Left (L), Right (R), coordinates (x, y, z) are given in Montreal Neurological Institute (MNI) space showing the center of each cluster.</p