No description available.

Motility and chemotaxis have been implicated in the process of biofilm formation in a wide range of species. Using a combination of microscopy and image analysis, genetics, microbiology and biochemistry, the initial approach of Rhodobacter sphaeroides cells to a solid surface has been characterised. Interestingly, these data suggest that for R. sphaeroides alterations in motility and swimming behaviour may result in differences in biofilm formation simply by changing the number of cells which reach the surface. This is in contrast to a few other well-studied species where the motility apparatus, the flagellum, has been shown to play an active role in surface sensing and the transition to biofilm growth. Tracking swimming cells and measuring surface attachment revealed that changes in motility affect the ability of cells to attach to a surface, with non-motile cells attaching least and mutants with frequent stops attaching less than smooth swimming cells with few stops. Tracking attaching cells and classifying their method of attachment revealed that flagellar tethering is not essential for R. sphaeroides attachment. Competition assays with fluorescently labelled strains showed that the initial imbalance between motile and non-motile cells remains as microcolonies develop over 48 hours,and the proportion of non-motile cells remains fairly constant. Development on a surface over 48 hours was similar for motile and non-motile strains, including aflagellate strains, once attached. Using parameters calculated by tracking swimming cells to calculate the effective diffusion coefficient in a simple model of cell movement suggested that motion alone could explain the differences in attachment without assuming different cell properties. In particular, aflagellate strains might be hindered from surface attachment by their reduced motility alone. This is interesting since some other bacterial species use the flagellum as a surface sensor.

One of the requirements for a successful artificial insemination is the quality of stallion´s ejaculate. This thesis deals with influence of sperm velocity fraction on fertility. Semen samples in this thesis were evaluated by using an objective computerized method CASA, system SCA. Sperm motility in monitoring was performed in 75 samples from 12 stallions involved in artificial insemination fresh sperm in ZH Písek. Total and progressive motility, rapid, medium and slow motility were monitored. Stallion´s age was from 3-21 years. The average of fertility was 56,19 %. The average of total motility was 78,07 %. The average of progressive motility was 38,35 %. Furthermore, the spermatozoa were divided into 3 velocity fractions and the average percentage of the individual fractions in the samples was as follows: 27,30 % rapid spermatozoa, 21,27 % medium spermatozoa and 29,50% slow spermatozoa. Then the average percentage of rapid progressive spermatozoa (13,43 %), medium progressive spermatozoa (24,92 %) and non-progressive spermatozoa (39,72 %) were found. There was a positive correlation between fertility and the rate of rapid motile spermatozoa (r=0,34). The difference between individual stallions (p-value < 0,01) in the mean percentage of rapid spermatozoa in the ejaculate was demonstrated. The stallion with the highest rate of rapid motile spermatozoa and the best pregnancy was welsh part-bred stallion. On the other hand, the worst pregnancy results and one of the lowest percentages of rapid motile spermatozoa had noriker stallion. The highest success rate of pregnancy was found after the second insemination.The results of this work have shown that the quality of the ejaculate has a very significant effect on good pregnancy but it is just one of many acting factors.

The Best PhD Thesis in the Faculties of Dentistry, Engineering, Medicine and Science (University of Hong Kong), Li Ka Shing Prize,2010-11 / published_or_final_version / Biochemistry / Doctoral / Doctor of Philosophy

Quantitative biology is an emerging field that attracts intensive research interests. Pattern formation is a widely studied topic both in biology and physics. Scientists have been trying to figure out the basic principles behind the fascinating patterns in the nature. It’s still difficult to lift the complex veil on the underling mechanisms, especially in biology, although lots of the achievements have been achieved. The new developments in synthetic biology provide a different approach to study the natural systems, test the theories, and develop new ones. Biological systems have many unique features different from physics and chemistry, such as growth and active movement. In this project, a link between cell density and cell motility is established through cell-cell signaling. The genetic engineered Escherichia coli cell regulates its motility by sensing the local cell density. The regulation of cell motility by cell density leads to sequential and periodical stripe patterns when the cells grow and expand on a semi-solid agar plate. This synthetic stripe pattern formation system is quantitative studied by quantitative measurements, mathematical modeling and theoretical analysis. To characterize the stripe pattern, two novel methods have been developed to quantify the key parameters, including cell growth, spatiotemporal cell density profile and cell density-dependent motility, besides the standard molecular biological measurements. To better understand the underlying principle of the stripe pattern formation, a quantitative model is developed based on the experiments. The detailed dynamic process is studied by computer simulation. Besides, the model predicts that the number of stripes can be tuned by varying the parameters in the system. This has been tested by quantitatively modulation of the basal expression level of a single gene in the genetic circuit. Moreover, theoretical analysis of a simplified model provides us a clear picture of the stripe formation process. The steady state traveling wave solution is obtained, which leads to an analytic ansatz that can determine the phase boundary between the stripe and the no-stripe phases. This study does not only provide a quantitative understanding about the novel mechanism of stripe pattern formation, but also sets an good example of quantitative studies in biology. The techniques, methods and knowledge gleaned here may be applied in various interdisciplinary fields. / published_or_final_version / Physics / Doctoral / Doctor of Philosophy

published_or_final_version / Medical Sciences / Master / Master of Medical Sciences

No description available.

No description available.

Bibliography: leaves 258-294. / xv, 294 leaves : ill. (1 col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Examines the organisation and control of the antropyloroduodenal motor unit in both healthy human volunteers and patients with gastroparesis. / Thesis (Ph.D.)--University of Adelaide, Dept. of Medicine, 1992

Diss. (sammanfattning) Uppsala : Univ., 2001. / Härtill 5 uppsatser.