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Title: The behaviour of microorganisms in microfluidic networks
Author: Binz, Marie
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2012
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This thesis focuses on the characterisation of microorganisms and their responses to poly( dimethylsiloxane) (PDMS) based three-dimensional microfluidic structures. Experiments based on observations of the responses of individual cells to their environment have the potential to make enormous contributions to cell biology and biomedicine. Chapter 1 presents the thesis aims. In chapter 2, an overview of bacteria and filamentous fungi including their physiology and motility mechanisms are presented. The applications of lithography techniques including soft-lithography for studying cells and microorganisms behaviour over flat and profiled surfaces as well as within microfluidic devices are also reviewed. Chapter 3 described the methodology for the fabrication and-manipulation of the PDMS-based networks "",,, employed for experimentation and for data analysis. Chapter 4 investigates the mechanisms that allow fungi to partition the space and negotiate micro-confined networks. Armillaria mellea has been introduced in networks of various shapes. A. mellea was able to grow through every network exhibiting similar geometry-induced mechanisms. The species growth behaviour was mainly influenced by the geometry of the networks which changed the tip extension velocity and the branching angles. The-results obtained suggest that thigmotropism in which hyphal growth occurs is an important parameter in fungal growth dynamics. The hyphae could also find their way toward a network without any wall contact. This suggests that sensing mechanisms does not rely exclusively on thigmotropism but also on the integration of the extra-cellular environment. In chapter 5 the swimming behaviour of Serratia marcescens and Pseudomonas stutzeri in different networks were compared to their behaviour in non-confined environment. Large channels of 100 urn in width had no effect on the bacterial species as the bacteria swam randomly over the surface with gradual changes in their swimming direction and were seen to trace out circular trajectories. Channels of less than 10 urn in width could control bacterial movements in one direction and close to the boundaries. Complex networks of different shape not only revealed similar behaviour for both species but also showed the ability of bacteria to turn corner, to perform 360 0 turn and to follow very intricate paths. The complexity of the network through which the bacteria swam as well as the channels size were identified as the dominating factors in predicting their motility. In chapter 6 the behaviour of S. marcescens swarming phenotype was investigated after modifying the extra-cellular environment of the networks. Changes in the viscosity of the solution to 3.7 cP for channels that are 15 urn in width showed elongated swarming cells of a size reaching 8 urn to 10 urn in length. 10 urn wide channels were used to observe the swimming-swarming behaviour of S. marcescens within a wide range of concentration of Ficoll 400 and caused a decrease in cell velocity in comparison to that measured in LB broth only. The maximum cells size observed was 5.3 urn. Chapter 7 summarises the thesis main findings and the contributions in the field. Future work is also described.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral