The main objective of this research was to determine the seed bank longevity of Melinis repens at two Southern Florida sites. Seeds were divided among different exposure levels (shade versus sun) and depths (surface versus buried) and tested for baseline viability using 2,3,5-Triphenyl-tetrazolium chloride. Statistical analysis determined that at the pine rockland site there was a significant interaction between time, exposure, and depth. The initial mean viability at this site declined from 49.71% to 11.26% and 13.06% for sun/buried seeds and sun/surface seeds, respectively, by month 8. The mean viability of shade/surface seeds and shade/buried seeds declined to 24.56% and 22.06% after 8 months. There were no significant effects in the Florida scrub. In order for land managers to completely remove this species from a site, treatment with herbicide will need to continue for a minimum of one year to effectively kill all viable seeds in the seed bank.

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Tip growth is a form of cellular expansion characteristic of fungal hyphae and some types of plant cells. Currently there is no unified model that satisfactorily describes this in hyphal species. Traditionally turgor has been considered an essential driving force behind cell expansion. In recent years this hypothesis has been challenged by evidence that in some species tip growth can occur despite the absence of measurable hydrostatic pressure. There are currently two contentious theories of hyphal extension. These are the turgor-driven model and the amoeboid-movement theory. Though the essential mechanism underlying cell growth differs between these theories, the actin cytoskeleton is considered important in both. It has been suggested that both the turgor-driven and amoeboid-like modes of growth could occur depending on the whether the hyphae are growing invasively or non-invasively respectively (Money, 1990). It has also been proposed that both modes may occur within the same mycelium (Garrill, 2000). Two distinct patterns of actin have been identified in the hyphal tips of oomycetes. This has lead to the hypothesis that two different mechanisms of apical extension may be employed by some hyphal organisms. During the course of this thesis, actin deplete zones have been observed in a significantly higher number of invasive compared to non-invasive hyphae of the oomycete Achlya bisexualis. Furthermore the difference between burst pressures was found to be lower in invasive hyphae compared to non-invasive hyphae suggestive of a weaker cell wall. A lack of significant difference in turgor pressures between the invasive and non-invasive hyphae of this organism suggests that the deplete zone and weaker wall plays a functional role in enabling hyphae to penetrate substrate. Fractal analysis of mycelial colonies shows that the variation in agar concentration and therefore substrate solidity has a significant effect on mycelial morphology. This is most likely due to an effect at the cellular level. The results of the experiments carried out during the course of this thesis provide the basis for future work towards elucidating the mechanisms of hyphal extension.

No description available.

No description available.

BACKGROUND: After the introduction of PCV7 and PCV13, the number of cases of pneumonia in children caused by vaccine serotypes has decreased significantly. Children with comorbidities, however, are still at high risk for IPD. This study aims to compare children with comorbidities to healthy children in an urban setting to assess current risk factors and potential risk factors for pneumonia. METHODS: Existing clinical data of Boston Medical Center patients under 7 years of age were used to compare age, gender, race, comorbidities, and immune status of children with pneumonia to those of children without pneumonia. A representative random sample of 150 patients with pneumonia and 150 patients without pneumonia was selected. Medical record and chart information were reviewed in order to obtain clinical and demographic data. RESULTS: In our study cohort, 120 of 300 (40%) children whose charts were reviewed had at least one comorbidity. Among 150 children with pneumonia, 76 (50.7%) cases were found to have at least one underlying condition, whereas in children without pneumonia 44 (29.3%) of 150 cases had at least one underlying clinical condition (chi-square value 14.2; p-value <0.001). Children with comorbidities were 2.47 times more likely to have pneumonia compared to children without any chronic conditions (OR 2.47, 95% CI 1.54 - 3.98). The risk of having pneumonia among children who are not Hispanic/Latino/Spanish was approximately 40% less compared to children of Hispanic origin (OR 0.61; 95% CI 0.31 - 1.19; p-value 0.14). CONCLUSIONS: Our study shows that children with underlying conditions are at greater risk for pneumonia compared to healthy children without chronic conditions. Ethnicity is also associated with pneumonia cases, with Hispanic children at increased risk for pneumonia compared to non-Hispanic children.

The course of pathogenic bacterial infection is dependent on the interactions between the host immune response and the bacterial virulence mechanisms. Our lab previously discovered that the Survival of Motor Neuron (SMN) protein complex undergoes a change in subcellular localization during infection with invasive Shigella bacteria, forming novel cytoplasmic aggregates called "U bodies". Similar results were obtained with other intracellular bacterial pathogens suggesting that these U bodies are a fundamental entity in microbial pathogenesis. Notably, the SMN complex normally plays a key role in the assembly of the spliceosomal U snRNA. We have shown during infection that there are changes in U snRNA maturation and splicing patterns. Importantly, we have found that U bodies are downstream of a stress pathway involving the stress-inducible ATF3 protein. Altogether, intracellular bacterial infection induces novel cellular stress pathways that disrupt normal SMN complex function and leads to changes in U snRNA associated functions.

The transportation of organisms in the ballast water of cargo ships has been recognized as a source of invasive species despite current control measures. Pathogenic bacteria in the ballast tank have been studied but the total diversity of the ballast tank bacterial community has not been examined. This study is the first to characterize the total bacterial community within a ballast tank by constructing a clone library from a ballast water sample from a cargo ship in the Port of Houston, amplified ribosomal rDNA restriction analysis (ARDRA) and phylogenetic analysis. Bacterial communities in Texas ports and bays were also examined using denaturing gradient gel electrophoresis (DGGE), looking at both temporal and spatial variations for effects of deballasting activity. This ballast tank bacterial community had a high level of diversity (95%) with the clone library only representing 40% of the total community of the tank. Most probable originating habitats of the ballast bacteria were: marine pelagic (40%), estuarine (37%), coastal (6%), freshwater (3%) and other (14%), even though this ballast tank was exchanged with pelagic water. Predominate groups were alpha- and gammaproteobacteria, a few betaproteobacteria and bacteriodetes, and one each of verrucomicrobia, planctomycetes and actinobacteria, but no pathogens were detected. The data reveals a ballast tank that consists of half marine-pelagic, half port bacteria, revealing a low efficacy of exchange control methods and potentially invasive bacteria. The bacterial communities of five ships that exchanged ballast water in the Pacific Ocean shared on average 50% similarity. Two ships that exchanged ballast water in temperate latitudes were more similar than three other ships that exchanged in tropical latitudes, showing a correlation between location of exchange and community similarity. The bacterial communities of the Ports of Houston and Galveston exhibit stable, seasonal successions over one year. The port and bay systems of Texas exhibited spatial variations in bacterial communities related to salinity levels. Both experiments did not show evidence of community disruption by deballasting activities. This study shows that ballast water is a viable vector for invasive bacterial transport, although impact on Texas estuarine systems seems minimal.

Thèse d'exercice : Médecine. Médecine générale : Université de Nantes : 2005. / Bibliogr. f. 103-110 [100 réf.].

Thesis (doctoral)--Technische Hochschule, Aachen, 1999.