3,160 research outputs found
Microbial biofilms
No full textBiofilms are usually thought of as the slimy layer of microorganisms that covers solid surfaces. However, there are a number of features that distinguish biofilm populations from their planktonic (suspended or free floating) counterparts, namely, the association with a surface, high population densities (on the order of 1010 cells per ml of hydrated biofilm), an extracellular polymer (EPS) slime matrix, and a wide range of physical, metabolic, and chemical heterogeneities. However, some biofilms may not have all features. Indeed, a concise universal definition of biofilms has yet to emerge; in part, this is because of the wide diversity of biofilm populations. Although much of contemporary microbiology is based on the study of planktonic “cells,” it is now thought that biofilms are the primary habitat for many microorganisms. Microbial mats associated with sediment and suspended microbial flocs or aggregates, although different in appearance from conventional biofilms, have many important features in common and thus are included in the definition of “biofilm.” Often biofilm cells are embedded within a highly hydrated EPS matrix, and in the absence of corrosion products or scale, biofilms are estimated to be primarily water. The physical properties of the biofilm are largely determined by the EPS, while the physiological properties are determined by the bacterial cells (Figs. 13.1 and 13.2)
Entertainer: Pieter-Dirk Uys
No full textThis booklet celebrates the life and work of Pieter-Dirk Uys, internationally acclaimed playwright, author, role-model and one of South Africa's living treasures
Entertainer: Pieter-Dirk Uys
No full textThis booklet celebrates the life and work of Pieter-Dirk Uys, internationally acclaimed playwright, author, role-model and one of South Africa's living treasures
Entertainer: Pieter-Dirk Uys
No full textThis booklet celebrates the life and work of Pieter-Dirk Uys, internationally acclaimed playwright, author, role-model and one of South Africa's living treasures
Formal Techniques and Self/Other Relations in the Novels of Dirk Bogarde
No full textThe thesis foregrounds the distinctive contribution Dirk Bogarde made to
contemporary writing in a second career that developed in parallel to his screen
commitments. It dispels the notion that Bogarde followed a familiar path as an actor
who wrote books. Instead it establishes his reputation as an innovative writer whose
formal technique was substantially influenced by the textual systems of cinema and
the cross-fertilisation from acting to writing.
In examining the formative factors that steered Bogarde towards authorship, the
thesis addresses the role of performance as a generative factor in the evolution of the
novels, establishing a discursive link with Bakhtinian dialogism, and specifically,
transgredience as a formal imperative. Secondly, it affords a critical insight into why
the major concerns with staging and performativity preoccupy his writing career.
The thesis claims that Bogarde was an empirically dialogical writer whose use
of camera-eye narration fostered the proliferation of competing discourses across the
fiction. This formal dynamic is centred on the relationship between stages and
dialogism, which incorporates the work of Erving Goffinan as a complementary
critique to Bakhtinian theory with its emphasis on self-presentation. The concern
with socially-constructed behaviour leads the thesis to address the associated issues of
stereotyping and 'otherness', which in terms of body politics is articulated by the
mono logic drive to confine the sexual 'other' to a fixed representation.
Bogarde's ability to draw on cinematic and performance techniques identifies
an area of expertise unavailable to most other writers. This is an unusual repository
of skills to bring to writing which is why the thesis makes the claim for his singular
achievement as a contemporary author. There are fruitful points of intersection to be
explored in this respect with the work of Christopher Isherwood, whom Bogarde read
and admired, as a basis for further research. It is hoped that the thesis will play its
part in opening up new possibilities for Bogarde's writing to be re-visited by future
critics
Effects of biofilm structures on oxygen distribution and mass transport
No full textAerobic biofilms were found to have a complex structure consisting of microbial cell clusters (discrete aggregates of densely packed cells) and interstitial voids. The oxygen distribution was strongly correlated with these structures. The voids facilitated oxygen transport from the bulk liquid through the biofilm, supplying approximately 50% of the total oxygen consumed by the cells. The mass transport rate from the bulk liquid is influenced by the biofilm structure; the observed exchange surface of the biofilm is twice that calculated for a simple planar geometry. The oxygen diffusion occurred in the direction normal to the cluster surfaces, the horizontal and vertical components of the oxygen gradients were of equal importance. Consequently, for calculations of mass transfer rates a three-dimensional model is necessary. These findings imply that to accurately describe biofilm activity, the relation between the arrangement of structural components and mass transfer must be understood. <br/
Bioenergetics of simultaneous oxygen and nitrate respiration and nitric oxide production in a <i>Pseudomonas aeruginosa</i> agar colony biofilm
No full textPseudomonas aeruginosa is a biofilm forming pathogen commonly associated with infection of the cystic fibrosis (CF) lung, chronic wounds and indwelling medical devices. P. aeruginosa is a facultative aerobe that can use nitrate (NO3−) found in healthy and infected tissues and body fluids to generate energy through denitrification. Further, P. aeruginosa the expression of denitrification genes has been found in specimens from people with CF. The main aim of this study was to determine the relative energy contribution of oxygen (O2) respiration and denitrification in single Pseudomonas aeruginosa PAO1 biofilm colonies under different O2 concentrations to estimate the possible relative importance of these metabolic processes in the context of biofilm infections. We showed that the used strain PAO1 in biofilms denitrified with nitrous oxide (N2O), and not nitrogen (N2), as the end product in our incubations. From simultaneous O2 and N2O microprofiles measured with high spatial resolution by microsensors in agar colony biofilms under air, N2 and pure O2, the rates of aerobic respiration and denitrification were calculated and converted to ATP production rates. Denitrification occurred both in the oxic and anoxic zones, and became increasingly dominant with decreasing O2 concentrations. At O2 concentrations characteristic for tissues and wounds (20–60 μM), denitrification was responsible for 50% of the total energy conservation in the biofilm. In addition the formation of nitric oxide (NO), a precursor of N2O and an important regulator of many cellular processes, was strongly influenced by the local O2 concentrations. NO production was inhibited under pure O2, present under anoxia (∼1 μM) and remarkably high (up to 6 μM) under intermediate O2 levels, which can be found in infected tissues. Possible impacts of such NO levels on both the host and the biofilm bacteria are discussed
Methane and sulfide fluxes in permanent anoxia: In situ studies at the Dvurechenskii mud volcano (Sorokin Trough, Black Sea)
No full textThe Dvurechenskii mud volcano (DMV) is located in permanently anoxic waters at 2060 m depth (Sorokin Trough, Black Sea). The DMV was studied during the RV Meteor expedition M72/2 as an example of an active mud volcano system, to investigate the significance of submarine mud volcanism for the methane and sulfide budget of the anoxic Black Sea hydrosphere. Our studies included benthic fluxes of methane and sulfide, as well as the factors controlling transport, consumption and production of both compounds within the sediment. The pie-shaped mud volcano showed temperature anomalies as well as solute and gas fluxes indicating high fluid flow at its summit north of the geographical center. The anaerobic oxidation of methane (AOM) coupled to sulfate reduction (SR) was repressed in this zone due to the upward flow of sulfate-depleted fluids through recently deposited subsurface muds, apparently limiting microbial methanotrophic activity. Consequently, the emission of dissolved methane into the water column was high, with an estimated rate of 0.46 mol m−2 d−1. On the wide plateau and edge of the mud volcano surrounding the summit, fluid flow and total methane flux were lower, allowing higher SR and AOM rates correlated with an increase in sulfate penetration into the sediment. Here, between 50% and 70% of the methane flux (0.07–0.1 mol m−2 d−1) was consumed within the upper 10 cm of the sediment. The overall amount of dissolved methane released from the entire mud volcano structure into the water column was significant with a discharge of 1.3 × 107 mol yr−1. The DMV maintains also high areal rates of methane-fueled sulfide production and emission of on average 0.05 mol m−2 d−1. This is a difference to mud volcanoes in oxic waters, which emit similar amounts of methane, but not sulfide. However, based on a comparison of this and other mud volcanoes of the Black Sea, we conclude that sulfide and methane emission into the hydrosphere from deep-water mud volcanoes does not significantly contribute to the sulfide and methane inventory of the Black Sea
Novel observations of Thiobacterium, a sulfur-storing Gammaproteobacterium producing gelatinous mats
No full textThe genus Thiobacterium includes uncultivated rod-shaped microbes containing several spherical grains of elemental sulfur and forming conspicuous gelatinous mats. Owing to the fragility of mats and cells, their 16S ribosomal RNA genes have not been phylogenetically classified. This study examined the occurrence of Thiobacterium mats in three different sulfidic marine habitats: a submerged whale bone, deep-water seafloor and a submarine cave. All three mats contained massive amounts of Thiobacterium cells and were highly enriched in sulfur. Microsensor measurements and other biogeochemistry data suggest chemoautotrophic growth of Thiobacterium. Sulfide and oxygen microprofiles confirmed the dependence of Thiobacterium on hydrogen sulfide as energy source. Fluorescence in situ hybridization indicated that Thiobacterium spp. belong to the Gammaproteobacteria, a class that harbors many mat-forming sulfide-oxidizing bacteria. Further phylogenetic characterization of the mats led to the discovery of an unexpected microbial diversity associated with Thiobacterium
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