RESUMO
Microbialites provide geological evidence of one of Earth's oldest ecosystems, potentially recording long-standing interactions between coevolving life and the environment. Here, we focus on microbialite accretion and growth and consider how environmental and microbial forces that characterize living ecosystems in Shark Bay and the Bahamas interact to form an initial microbialite architecture, which in turn establishes distinct evolutionary pathways. A conceptual three-dimensional model is developed for microbialite accretion that emphasizes the importance of a dynamic balance between extrinsic and intrinsic factors in determining the initial architecture. We then explore how early taphonomic and diagenetic processes modify the initial architecture, culminating in various styles of preservation in the rock record. The timing of lithification of microbial products is critical in determining growth patterns and preservation potential. Study results have shown that all microbialites are not created equal; the unique evolutionary history of an individual microbialite matters.
Assuntos
Baías , Ecossistema , Bahamas , Evolução Biológica , Sedimentos GeológicosRESUMO
Reputed to be the driest desert in the world, the Atacama Desert in the Central Andes of Northern Chile is an extreme environment with high UV radiation, wide temperature variation, and minimum precipitation. Scarce lagoons associated with salt flats (salars) in this desert are the surface expression of shallow groundwater; these ponds serve as refugia for life and often host microbial communities associated with evaporitic mineral deposition. Results based on multidisciplinary field campaigns and associated laboratory examination of samples collected from the Puquios of the Salar de Llamara in the Atacama Desert during austral summer provide unprecedented detail regarding the spatial heterogeneity of physical, chemical, and biological characteristics of these salar environments. Four main lagoons ('Puquios') and more than 400 smaller ponds occur within an area less than 5 km2, and are characterized by high variability in electrical conductivity, benthic and planktonic biota, microbiota, lagoon bottom type, and style of mineral deposition. Results suggest that electrical conductivity is a driving force of system heterogeneity. Such spatial heterogeneity within the Puquios is likely to be expanded with temporal observations incorporating expected seasonal changes in electrical conductivity. The complexity of these Andean ecosystems may be key to their ability to persist in extreme environments at the edge of habitability.
RESUMO
Thrombolites are buildups of carbonate that exhibit a clotted internal structure formed through the interactions of microbial mats and their environment. Despite recent advances, we are only beginning to understand the microbial and molecular processes associated with their formation. In this study, a spatial profile of the microbial and metabolic diversity of thrombolite-forming mats of Highborne Cay, The Bahamas, was generated by using 16S rRNA gene sequencing and predictive metagenomic analyses. These molecular-based approaches were complemented with microelectrode profiling and in situ stable isotope analysis to examine the dominant taxa and metabolic activities within the thrombolite-forming communities. Analyses revealed three distinctive zones within the thrombolite-forming mats that exhibited stratified populations of bacteria and archaea. Predictive metagenomics also revealed vertical profiles of metabolic capabilities, such as photosynthesis and carboxylic and fatty acid synthesis within the mats that had not been previously observed. The carbonate precipitates within the thrombolite-forming mats exhibited isotopic geochemical signatures suggesting that the precipitation within the Bahamian thrombolites is photosynthetically induced. Together, this study provides the first look at the spatial organization of the microbial populations within Bahamian thrombolites and enables the distribution of microbes to be correlated with their activities within modern thrombolite systems. Key Words: Thrombolites-Microbial diversity-Metagenome-Stable isotopes-Microbialites. Astrobiology 17, 413-430.
Assuntos
Bactérias , Metagenômica , Bahamas , Sedimentos Geológicos , Isótopos , Filogenia , RNA Ribossômico 16SRESUMO
Modern stromatolites represent ideal ecosystems to understand the biological processes required for the precipitation of carbonate due to their long evolutionary history and occurrence in a wide range of habitats. However, most of the prior molecular work on stromatolites has focused on understanding the taxonomic complexity and not fully elucidating the functional capabilities of these systems. Here, we begin to characterize the microbiome associated with stromatolites of Little Darby Island, The Bahamas using predictive metagenomics of the 16S rRNA gene coupled with direct whole shotgun sequencing. The metagenomic analysis of the Little Darby stromatolites revealed many shared taxa and core pathways associated with biologically induced carbonate precipitation, suggesting functional convergence within Bahamian stromatolites. A comparison of the Little Darby stromatolites with other lithifying microbial ecosystems also revealed that although factors, such as geographic location and salinity, do drive some differences within the population, there are extensive similarities within the microbial populations. These results suggest that for stromatolite formation, 'who' is in the community is not as critical as metabolic activities and environmental interactions. Together, these analyses help improve our understanding of the similarities among lithifying ecosystems and provide an important first step in characterizing the shared microbiome of modern stromatolites.
Assuntos
Sedimentos Geológicos/microbiologia , Metagenômica/métodos , Microbiota/genética , Bahamas , Evolução Biológica , Ilhas , RNA Ribossômico 16S/genéticaRESUMO
Microbialites are sedimentary deposits formed by the metabolic interactions of microbes and their environment. These lithifying microbial communities represent one of the oldest ecosystems on Earth, yet the molecular mechanisms underlying the function of these communities are poorly understood. In this study, we used comparative metagenomic and metatranscriptomic analyses to characterize the spatial organization of the thrombolites of Highborne Cay, The Bahamas, an actively forming microbialite system. At midday, there were differences in gene expression throughout the spatial profile of the thrombolitic mat with a high abundance of transcripts encoding genes required for photosynthesis, nitrogen fixation and exopolymeric substance production in the upper three mm of the mat. Transcripts associated with denitrification and sulfate reduction were in low abundance throughout the depth profile, suggesting these metabolisms were less active during midday. Comparative metagenomics of the Bahamian thrombolites with other known microbialite ecosystems from across the globe revealed that, despite many shared core pathways, the thrombolites represented genetically distinct communities. This study represents the first time the metatranscriptome of living microbialite has been characterized and offers a new molecular perspective on those microbial metabolisms, and their underlying genetic pathways, that influence the mechanisms of carbonate precipitation in lithifying microbial mat ecosystems.
Assuntos
Metabolismo Energético/genética , Sedimentos Geológicos/microbiologia , Metaboloma/genética , Água do Mar/microbiologia , Transcriptoma/genética , Bahamas , Metagenômica/métodosRESUMO
Microbialites are the most abundant macrofossils of the Precambrian. Decline in microbialite abundance and diversity during the terminal Proterozoic and early Phanerozoic has historically been attributed to the concurrent radiation of complex metazoans. Similarly, the apparent resurgence of microbialites in the wake of Paleozoic and Mesozoic mass extinctions is frequently linked to drastic declines in metazoan diversity and abundance. However, it has become increasing clear that microbialites are relatively common in certain modern shallow, normal marine carbonate environments-foremost the Bahamas. For the first time, we present data, collected from the Exuma Cays, the Bahamas, systematically characterizing the relationship between framework-building cyanobacteria, microbialite fabrics, and microbialite-associated metazoan abundance and diversity. We document the coexistence of diverse microbialite and infaunal metazoan communities and demonstrate that the predominant control upon both microbialite fabric and metazoan community structure is microbial mat type. These findings necessitate that we rethink prevalent interpretations of microbialite-metazoan interactions and imply that microbialites are not passive recipients of metazoan-mediated alteration. Additionally, this work provides support for the theory that certain Precambrian microbialites may have been havens of early complex metazoan life, rather than bereft of metazoans, as has been traditionally envisaged.
Assuntos
Biodiversidade , Biofilmes/crescimento & desenvolvimento , Cianobactérias/fisiologia , Invertebrados/fisiologia , Animais , Bahamas , Cianobactérias/crescimento & desenvolvimento , Invertebrados/classificação , Água do MarRESUMO
Stromatolites are laminated organosedimentary structures formed by microbial communities, principally cyanobacteria although eucaryote phototrophs may also be involved in the construction of modern stromatolites. In this study, productivity and photophysiology of communities from stromatolites (laminated) and thrombolites (nonlaminated) were analysed using fluorescence imaging. Sub-samples of mats were excised at Highborne Cay, Bahamas, and cross-sectioned to simultaneously analyse surface, near-surface (1-2 mm), and deeper (2-10 mm) communities. Rapid light curve parameters and nonphotochemical downregulation showed distinct differences between phototroph communities, consistent with the reported quasi-succession of classic stromatolite mat types. Greater productivity was shown by cyanobacteria in Type 1 and Type 3 mats (first and final stage of the succession, Schizothrix gebeleinii and Solentia sp. respectively) and lower productivity within Type 2 mats (intermediate mat type). Eucaryote mat types, dominated by stalked (Striatella sp. and Licmophora sp.) and tube-dwelling (e.g. Nitzschia and Navicula spp.) diatoms, showed greater productivity than cyanobacteria communities, with the exception of Striatella (low productivity) and an unidentified coccoid cyanobacterium (high productivity). Findings indicate comparative variability between photosynthetically active procaryote and eucaryote sub-communities within stromatolites, with a pattern logically following the succession of 'classic' mat types, and lower than the productivity of eucaryote dominated 'nonclassic' mat types.
Assuntos
Cianobactérias/fisiologia , Diatomáceas/fisiologia , Ecossistema , Água do Mar/microbiologia , Bahamas , Clorofila/análise , Cianobactérias/química , Cianobactérias/isolamento & purificação , Diatomáceas/química , Diatomáceas/classificação , Diatomáceas/isolamento & purificação , Fluorometria/métodosRESUMO
Thrombolites are unlaminated carbonate build-ups that are formed via the metabolic activities of complex microbial mat communities. The thrombolitic mats of Highborne Cay, Bahamas develop in close proximity (1-2 m) to accreting laminated stromatolites, providing an ideal opportunity for biogeochemical and molecular comparisons of these two distinctive microbialite ecosystems. In this study, we provide the first comprehensive characterization of the biogeochemical activities and microbial diversity of the Highborne Cay thrombolitic mats. Morphological and molecular analyses reveal two dominant mat types associated with the thrombolite deposits, both of which are dominated by bacteria from the taxa Cyanobacteria and Alphaproteobacteria. Diel cycling of dissolved oxygen (DO) and dissolved inorganic carbon (DIC) were measured in all thrombolitic mat types. DO production varied between thrombolitic types and one morphotype, referred to in this study as 'button mats', produced the highest levels among all mat types, including the adjacent stromatolites. Characterization of thrombolite bacterial communities revealed a high bacterial diversity, roughly equivalent to that of the nearby stromatolites, and a low eukaryotic diversity. Extensive phylogenetic overlap between thrombolitic and stromatolitic microbial communities was observed, although thrombolite-specific cyanobacterial populations were detected. In particular, the button mats were dominated by a calcified, filamentous cyanobacterium identified via morphology and 16S rRNA gene sequencing as Dichothrix sp. The distinctive microbial communities and chemical cycling patterns within the thrombolitic mats provide novel insight into the biogeochemical processes related to the lithifying mats in this system, and provide data relevant to understanding microbially induced carbonate biomineralization.
Assuntos
Bactérias/classificação , Biodiversidade , Eucariotos/classificação , Sedimentos Geológicos/microbiologia , Microbiologia do Solo , Bactérias/citologia , Bactérias/genética , Bactérias/isolamento & purificação , Bahamas , Carbono/metabolismo , Análise por Conglomerados , DNA/química , DNA/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Eucariotos/citologia , Eucariotos/genética , Eucariotos/isolamento & purificação , Dados de Sequência Molecular , Oxigênio/metabolismo , Filogenia , RNA Ribossômico 16S/genética , RNA Ribossômico 18S/genética , Análise de Sequência de DNA , Homologia de SequênciaRESUMO
Calcified cyanobacterial microfossils are common in carbonate environments through most of the Phanerozoic, but are absent from the marine rock record over the past 65 Myr. There has been long-standing debate on the factors controlling the formation and temporal distribution of these fossils, fostered by the lack of a suitable modern analog. We describe calcified cyanobacteria filaments in a modern marine reef setting at Highborne Cay, Bahamas. Our observations and stable isotope data suggest that initial calcification occurs in living cyanobacteria and is photosynthetically induced. A single variety of cyanobacteria, Dichothrix sp., produces calcified filaments. Adjacent cyanobacterial mats form well-laminated stromatolites, rather than calcified filaments, indicating there can be a strong taxonomic control over the mechanism of microbial calcification. Petrographic analyses indicate that the calcified filaments are degraded during early diagenesis and are not present in well-lithified microbialites. The early diagenetic destruction of calcified filaments at Highborne Cay indicates that the absence of calcified cyanobacteria from periods of the Phanerozoic is likely to be caused by low preservation potential as well as inhibited formation.
Assuntos
Cálcio/análise , Cianobactérias/química , Fósseis , Sedimentos Geológicos/microbiologia , Bahamas , Isótopos de Carbono/análise , Cianobactérias/citologia , Cianobactérias/ultraestrutura , Microscopia , Microscopia Eletrônica de VarreduraRESUMO
Living marine stromatolites at Highborne Cay, Bahamas, are formed by microbial mat communities that facilitate precipitation of calcium carbonate and bind and trap small carbonate sand grains. This process results in a laminated structure similar to the layering observed in ancient stromatolites. In the modern marine system at Highborne Cay, lamination, lithification and stromatolite formation are associated with cycling between three types of microbial communities at the stromatolite surface (Types 1, 2 and 3, which range from a leathery microbial mat to microbially fused sediment). Examination of 923 universal small-subunit rRNA gene sequences from these communities reveals that taxonomic richness increases during transition from Type 1 to Type 3 communities, supporting a previous model that proposed that the three communities represent different stages of mat development. The phylogenetic composition also changes significantly between these community types and these community changes occur in concert with variation in biogeochemical rates. The dominant bacterial groups detected in the stromatolites include Alphaproteobacteria, Planctomycetes, Cyanobacteria and Bacteroidetes. In addition, the stromatolite communities were found to contain novel cyanobacteria that may be uniquely associated with modern marine stromatolites. The implications of these findings are discussed in the context of current models for stromatolite formation.
Assuntos
Bactérias/crescimento & desenvolvimento , Biodiversidade , Sedimentos Geológicos/microbiologia , Alphaproteobacteria/genética , Alphaproteobacteria/crescimento & desenvolvimento , Alphaproteobacteria/isolamento & purificação , Bactérias/genética , Bactérias/isolamento & purificação , Bacteroidetes/genética , Bacteroidetes/crescimento & desenvolvimento , Bacteroidetes/isolamento & purificação , Bahamas , Cianobactérias/genética , Cianobactérias/crescimento & desenvolvimento , Cianobactérias/isolamento & purificação , DNA Bacteriano/genética , DNA Bacteriano/isolamento & purificação , Genes de RNAr , Dados de Sequência Molecular , Filogenia , Análise de Sequência de DNARESUMO
Stromatolites are sedimentary deposits that are the direct result of interactions between microbes and their surrounding environment. Once dominant on ancient Earth, actively forming stromatolites now occur in just a few remote locations around the globe, such as the island of Highborne Cay, Bahamas. Although the stromatolites of Highborne Cay contain a wide range of metabolically diverse organisms, photosynthetic cyanobacteria are the driving force for stromatolite development. In this study, we complement previous morphological data by examining the cyanobacterial phylogenetic and physiological diversity of Highborne Cay stromatolites. Molecular analysis of both clone and culture libraries identified 33 distinct phylotypes within the stromatolites. Culture libraries exhibited several morphologically similar but genetically distinct ecotypes, which may contribute to ecosystem stability within the stromatolites. Several of the cultured isolates exhibited both a positive phototactic response and light-dependent extracellular polymeric secretions production, both of which are critical phenotypes for stromatolite accretion and development. The results of this study reveal that the genetic diversity of the cyanobacterial populations within the Highborne Cay stromatolites is far greater than previous estimates, indicating that the mechanisms of stromatolite formation and accretion may be more complex than had been previously assumed.
Assuntos
Biodiversidade , Cianobactérias/classificação , Cianobactérias/isolamento & purificação , Sedimentos Geológicos/microbiologia , Bahamas , Biopolímeros/metabolismo , Análise por Conglomerados , Cianobactérias/genética , Cianobactérias/fisiologia , DNA Bacteriano/química , DNA Bacteriano/genética , DNA Ribossômico/química , DNA Ribossômico/genética , Genes de RNAr , Luz , Dados de Sequência Molecular , Filogenia , RNA Bacteriano/genética , RNA Ribossômico 16S/genética , Análise de Sequência de DNA , Homologia de Sequência do Ácido NucleicoRESUMO
For the first time we have investigated the natural ecosystem engineering capacity of stromatolitic microbial assemblages. Stromatolites are laminated sedimentary structures formed by microbial activity and are considered to have dominated the shallows of the Precambrian oceans. Their fossilised remains are the most ancient unambiguous record of early life on earth. Stromatolites can therefore be considered as the first recognisable ecosystems on the planet. However, while many discussions have taken place over their structure and form, we have very little information on their functional ecology and how such assemblages persisted despite strong eternal forcing from wind and waves. The capture and binding of sediment is clearly a critical feature for the formation and persistence of stromatolite assemblages. Here, we investigated the ecosystem engineering capacity of stromatolitic microbial assemblages with respect to their ability to stabilise sediment using material from one of the few remaining living stromatolite systems (Highborne Cay, Bahamas). It was shown that the most effective assemblages could produce a rapid (12-24 h) and significant increase in sediment stability that continued in a linear fashion over the period of the experimentation (228 h). Importantly, it was also found that light was required for the assemblages to produce this stabilisation effect and that removal of assemblage into darkness could lead to a partial reversal of the stabilisation. This was attributed to the breakdown of extracellular polymeric substances under anaerobic conditions. These data were supported by microelectrode profiling of oxygen and calcium. The structure of the assemblages as they formed was visualised by low-temperature scanning electron microscopy and confocal laser microscopy. These results have implications for the understanding of early stromatolite development and highlight the potential importance of the evolution of photosynthesis in the mat forming process. The evolution of photosynthesis may have provided an important advance for the niche construction activity of microbial systems and the formation and persistence of the stromatolites which came to dominate shallow coastal environments for 80% of the biotic history of the earth.
Assuntos
Sedimentos Geológicos/microbiologia , Fotossíntese , Microbiologia da Água , Bahamas , Evolução Biológica , Ecossistema , Evolução Planetária , Fósseis , Sedimentos Geológicos/química , Geologia , Luz , Microscopia Confocal , Oxigênio , PaleontologiaRESUMO
To help define the habitat of modern marine stromatolites, wave-dominated flow and sediment transport were studied in the shallow subtidal region (1-2 m depth) along the slightly concave, windward face of Highborne Cay, Exuma, Bahamas - the only face of the cay that includes a population of stromatolites concentrated near the region of highest curvature of the beach. Wave energy impacting this island's most exposed beach was driven by local wind forcing which increases largely in response to the passage of atmospheric disturbances that typically affect the region for periods of a few days. Although some wave energy is almost always noted (maximum horizontal orbital speeds at the bottom are rarely <10 cm s(-1)), wave conditions remain comparatively calm until local winds increase above speeds of approximately 3-4 m s(-1) at which point maximum wave speeds rapidly increase to 50-80 cm s(-1). Stromatolites, which are largely restricted to the shoreward side of a shallow platform reef, are sheltered by the reef beyond which wave speeds are one to four times higher (depending on tidal stage). Moreover, stromatolite populations are predominantly found along a region of this wave-exposed beach that experiences comparatively reduced wave energy because of the curved morphology of the island's face. Maximum wave speeds are 1.4 to 2 times higher along more northern sections of the beach just beyond the locus of stromatolite populations. A quantitative model of sediment transport was developed that accurately predicted accumulation of suspended sediment in sediment traps deployed in the shallow subtidal zone along this beach. This model, coupled with in situ wave records, indicates that gross rates of suspended sediment deposition should be two to three times higher northward of the main stromatolite populations. Regions of the beach containing stromatolites nevertheless should experience significant rates of gross suspended sediment deposition averaging 7-10 g cm(-2) day(-1) ( approximately 4-6 cm day(-1)). Results suggest that one axis of the habitat of modern marine stromatolites may be defined by a comparatively narrow range of flow energy and sediment transport conditions.
Assuntos
Microbiologia Ambiental , Sedimentos Geológicos/microbiologia , Modelos Teóricos , Movimentos da Água , Bahamas , Fósseis , Fluxometria por Laser-Doppler , VentoRESUMO
Viruses, and more particularly phages (viruses that infect bacteria), represent one of the most abundant living entities in aquatic and terrestrial environments. The biogeography of phages has only recently been investigated and so far reveals a cosmopolitan distribution of phage genetic material (or genotypes). Here we address this cosmopolitan distribution through the analysis of phage communities in modern microbialites, the living representatives of one of the most ancient life forms on Earth. On the basis of a comparative metagenomic analysis of viral communities associated with marine (Highborne Cay, Bahamas) and freshwater (Pozas Azules II and Rio Mesquites, Mexico) microbialites, we show that some phage genotypes are geographically restricted. The high percentage of unknown sequences recovered from the three metagenomes (>97%), the low percentage similarities with sequences from other environmental viral (n = 42) and microbial (n = 36) metagenomes, and the absence of viral genotypes shared among microbialites indicate that viruses are genetically unique in these environments. Identifiable sequences in the Highborne Cay metagenome were dominated by single-stranded DNA microphages that were not detected in any other samples examined, including sea water, fresh water, sediment, terrestrial, extreme, metazoan-associated and marine microbial mats. Finally, a marine signature was present in the phage community of the Pozas Azules II microbialites, even though this environment has not been in contact with the ocean for tens of millions of years. Taken together, these results prove that viruses in modern microbialites display biogeographical variability and suggest that they may be derived from an ancient community.
Assuntos
Bacteriófagos/isolamento & purificação , Bacteriófagos/fisiologia , Biodiversidade , Ecossistema , Geografia , Microbiologia da Água , Bacteriófagos/classificação , Bacteriófagos/genética , Bahamas , Capsídeo/química , Biologia Computacional , DNA Viral/análise , DNA Viral/genética , Água Doce/microbiologia , Água Doce/virologia , Genoma Viral/genética , Genômica , Sedimentos Geológicos/microbiologia , Sedimentos Geológicos/virologia , México , Dados de Sequência Molecular , Filogenia , Proteoma/metabolismo , Água do Mar/microbiologia , Água do Mar/virologiaRESUMO
BACKGROUND: Exercise tolerance in patients with COPD is highly variable and poorly related to airways obstruction assessed by FEV1. These patients develop dynamic hyperinflation (DH) during an incremental exercise test which can be evaluated through a reduction in inspiratory capacity (IC). AIM: To evaluate: a) if the six minute walking test (6 MWD) induce DH reducing IC, b) if the reduction in IC is related to tidal expiratory flow limitation at rest (FL). SUBJECTS AND METHODS: Thirty eight stable COPD patients (28 FL and ten non FL during resting breathing, determined by the negative pressure technique). Inspiratory capacity was measured before and immediately after the 6 MWD test. Dyspnea, SpO2 and heart rate were measured before and after the test. RESULTS: Inspiratory capacity was lower in FL patients as compared to patients without FL (p < 0.005). Although no differences were found between groups in 6 MWD, dyspnea and HR, a significant reduction in IC after the walking test was observed only in FL patients (p < 0.0001). In addition, SpO2 fell significantly (p < 0.0001) after walking in the same group. CONCLUSIONS: Our results demonstrate that a moderate exercise such as the walking test induces DH and hypoxemia in patients with COPD and FL and stresses the importance of assessing DH by measuring IC in these patients.
Assuntos
Tolerância ao Exercício/fisiologia , Pneumopatias Obstrutivas/fisiopatologia , Idoso , Estudos de Casos e Controles , Dispneia/etiologia , Teste de Esforço , Feminino , Humanos , Capacidade Inspiratória , Masculino , Ventilação Pulmonar , Descanso , Espirometria , Estatísticas não Paramétricas , Capacidade Pulmonar Total , CaminhadaRESUMO
For three billion years, before the Cambrian diversification of life, laminated carbonate build-ups called stromatolites were widespread in shallow marine seas. These ancient structures are generally thought to be microbial in origin and potentially preserve evidence of the Earth's earliest biosphere. Despite their evolutionary significance, little is known about stromatolite formation, especially the relative roles of microbial and environmental factors in stromatolite accretion. Here we show that growth of modern marine stromatolites represents a dynamic balance between sedimentation and intermittent lithification of cyanobacterial mats. Periods of rapid sediment accretion, during which stromatolite surfaces are dominated by pioneer communities of gliding filamentous cyanobacteria, alternate with hiatal intervals. These discontinuities in sedimentation are characterized by development of surface films of exopolymer and subsequent heterotrophic bacterial decomposition, forming thin crusts of microcrystalline carbonate. During prolonged hiatal periods, climax communities develop, which include endolithic coccoid cyanobacteria. These coccoids modify the sediment, forming thicker lithified laminae. Preservation of lithified layers at depth creates millimetre-scale lamination. This simple model of modern marine stromatolite growth may be applicable to ancient stromatolites.
Assuntos
Carbonatos , Cianobactérias , Biologia Marinha , Microbiologia da Água , Bahamas , Evolução Biológica , Fósseis , Sedimentos GeológicosRESUMO
OBJECTIVES: We compared the efficacy, safety, and immunogenicity of a rhesus rotavirus tetravalent vaccine (RRV-TV), a rhesus rotavirus monovalent (serotype 1) vaccine (RRV-S1), and placebo in healthy American Indian infants for two rotavirus seasons. STUDY DESIGN: Infants aged 6 to 24 weeks were enrolled in a randomized, double-blind efficacy study. Infants were orally administered RRV-TV (4 x 10(5) plaque-forming units per dose), RRV-S1 (4 x 10(5) plaque-forming units per dose), or placebo at 2, 4, and 6 months of age. Stools collected during episodes of gastroenteritis were tested for detection of rotavirus antigen. A total of 1185 infants received at least one dose of a study vaccine or placebo, and 1051 received all three doses according to the protocol. RESULTS: During the first year of surveillance, the estimates of vaccine efficacy (with 95% confidence interval) for preventing rotaviral gastroenteritis were 50% (26, 67) for RRV-TV and 29% (-1, 50) for RRV-S1. In this population only 6% of rotaviral gastroenteritis episodes among placebo recipients were associated with type G1 disease. For severe disease the estimates of vaccine efficacy were higher: 69% (29, 88) for RRV-TV and 48% (-4, 75) for RRV-S1. CONCLUSIONS: These data indicate that RRV-TV is moderately efficacious in preventing all episodes of gastroenteritis caused by rotavirus and is most efficacious against the severe disease characteristic of rotaviral illness.
Assuntos
Indígenas Norte-Americanos , Infecções por Rotavirus/prevenção & controle , Vacinas contra Rotavirus , Vacinas Atenuadas/administração & dosagem , Vacinas Virais/administração & dosagem , Método Duplo-Cego , Gastroenterite/diagnóstico , Humanos , Lactente , Estudos Retrospectivos , Infecções por Rotavirus/imunologia , Índice de Gravidade de Doença , Vacinas Atenuadas/efeitos adversos , Vacinas Virais/efeitos adversosRESUMO
We measured total serum IgE in 14 patients with allergic diseases and 16 healthy subjects, using 3 commercial ELISA kits. The correlation of results among the 3 kits was analized using Passing and Bablock regression parameters. Results show that measurements of the different kits do not coincide. One kit shows differences using sera from allergic patients. It is concluded that it is not possible to determine exactly the amount of IgE using these kits, specially in subjects with elevated levels
Assuntos
Humanos , Masculino , Feminino , Adulto , Imunoglobulina E/análise , Ensaio de Imunoadsorção Enzimática , Hipersensibilidade Imediata/imunologia , Estudos de Casos e ControlesRESUMO
Intertidal stromatolites, covered by cyanobacterial mats, were recently discovered at Stocking Island, Exuma Cays, Bahamas. Ecophysiological responses (CO2 fixation, N2 fixation, and photoacclimation) of these cyanobacterial mats to experimental manipulations were examined to identify potential environmental variables controlling community structure and function. The mats exhibit horizontal zonation that shifts from soft to crusty to hard in a seaward direction. Cluster analysis of chemotaxonomic photopigments (chlorophylls and carotenoids) revealed that visually distinct mat types are composed of distinct phototrophic assemblages. Under reduced irradiance, diatoms within the mats photoacclimated by increasing accessory photopigments (diadinoxanthin, fucoxanthin, and chlorophyll c 1 c 2) and cyanobacteria reduced the photoprotective carotenoid echinenone. In a 4-day nutrient addition bioassay experiment, nitrate, phosphate, dissolved organic carbon, and trace metal enrichments did not enhance CO2 fixation, but phosphate enrichments tripled N2 fixation rates. The addition of DCMU increased N2 fixation rates relative to nonamended light and dark rates, indicating light (photosystem I) enhanced nitrogenase activity. Soft mats appear to represent the early stages of colonization and stabilization of mat communities. Active growth following stabilization results in the formation of partially-lithified crusty mats, which eventually become highly-lithified and form hard mats. Collectively, our results suggest that Stocking Island stromatolitic mats have low growth rates and consequently exhibit slow responses to increased nutrient availability and changes in ambient irradiance. In general, intertidal stromatolitic mats at Stocking Island appear to exhibit low rates of CO2 and N2 fixation relative to nonlithifying temperate cyanobacteral mats. Although production is low, respiration is likewise low, leading to the suggestion that high production to respiration ratios (P:R) may be necessary for lithification of intertidal stromatolitic mats.
RESUMO
The incidence of invasive Haemophilus influenzae type b (Hib) infection was decreased significantly among Navajo children since the licensure of Hib conjugate vaccines, even though two lots of Hib (polyribosylribitol phosphate)-meningococcal B outer-membrane protein conjugate vaccine (PRP-OMP) widely used among the Navajo were later found to be of low immunogenicity. We measured the effectiveness of all Hib conjugate vaccines combined, PRP-OMP alone, and the PRP-OMP lots with lower-than-expected immunogenicity among Navajo infants and children. This was a matched case-control study using active, laboratory-based surveillance for the ascertainment of Navajo children 2 1/2 to 59 months of age with invasive Hib infection; 45 patients with infection and 180 control subjects were enrolled. The effectiveness of one, two, and three doses, respectively, of all Hib conjugate vaccines combined was 96% (95% confidence interval (CI) 65%, 99%), 99% (95% CI, 69%, 100%), and 99% (95% CI - 57%, 100%). The effectiveness of one or more doses of PRP-OMP was 95% (95% CI, 66%, 99%). The effectiveness of a single dose of the lots of lower-than-expected immunogenicity was 89% (95% CI, -8%, 99%). The Hib conjugate vaccine coverage increased from 49% during 1991 to 94% during 1992; no control subjects younger than 18 months of age were enrolled during 1993. The occurrence of invasive Hib infections in this population after licensure of Hib conjugate vaccines was the result of gradual vaccine uptake, not poor vaccine effectiveness. The use of PRP-OMP has been highly effective despite concerns about the immunogenicity of several lots.