The contents of this thesis have been divided into 2 parts . The first part deals with genetic studies carried out on 36 strains belonging to the Bacteroides fragilis group. A number of mutants were isolated from several of the strains. A notable feature of the methods used was the low yield of mutants obtained and the marked sensitivity of these organisms to the mutagenic agents. Variations in colonial morphology was found to be a common feature amongst these organisms. In a few strains this phenomenon was clearly visible, in the remainder it was much weaker, and often could only be seen with the aid of a microscope . Colonial variation was found to be due to the ability of a proporti on of the cells to pruduce capsules or slime layers. The variants were found to segregate at high frequency and different growth conditions were found to have little effect on the segregation frequency or capsule formation . A number of phages specific for B. fragilis and B. t hetaiotaomicron were isol ated. All these phages were virulent and attempts to induce lysogenic phages were unsuccesful . The use of these phages in attempts to obtain transduction proved unsuccessful. A phage carrier state was found to occur in the majority of the phage-host cell systems, which seemed to be due to the presence of phage-resistant encapsulated cells in the population. Bacteriocins were produced by about half the strains, these inhibited the growth of a high proportion of the 36 strains tested. The bacteriocins were released into the growth media at the end of the growth period in the 2 bacteriocins tested. A link between the mode of action of one bacteriocin and rifampicin-resistance was investigated. All the bacter iocins tested were found to be inactive against some rifampicin-resistant mutants of a susceptible strain, suggesting a common mode of action. The presence of capsules in some cells appeared to confer bacteriocin-resistance on these variants. The second part of the thesis deals with a study of the physiological responses of a single strain of B.fragilis to ultraviolet radiation. This strain was found to be more sensitive to ultraviolet radiation under aerobic conditions. The amount of pyrimidine dimers formed after irradiation under anaerobic and aerobic conditions, was not found to differ significantly, indicating that the increase in sensitivity under aerobic conditions was not due to an increase in DNA damage. The use of repair inhibitors and the survival characteristics indicate that this difference was due to decreased repair capabilities under aerobic conditions. Liquid holding recovery in B.fragiZis was found to occur under aerobic conditions . This process was brought about by excision repair and appeared to be due to a decrease in repair efficiency under aerobic conditions. Under anaerobic conditions, where full repair capabilities were present, liquid holding recovery was inhibited. Both minimal medium recovery and fluence dependent filament formation were found to occur in irradiated B.fragiZis cells. The survival kinetics of a number of irradiated B.fragiZis phages were determined and a number of phage reactivation processes were investigated. Little or no host cell reactivation appeared to occur in the strains investigated, however, some ultraviolet reactivation and multiplicity reactivation was found to occur, but only under anaerobic conditions. Photoreactivation was found to be absent in this organism, but an excision repair system was present . The excision repair system was partially characterized and was found to resemble short patch excision repair in E.coli. Evidence was found which suggested that a second mode of repair which was sensitive to oxygen, also occurred in this strain. This repair system which appeared to be responsible for error-prone repair, and the systems which were responsible for ultraviolet reactivation and multiplicity reactivation, seemed to be dependent on a recombination function' which was inhibited by oxygen. The significance of this finding for future genetic studies was discussed.

A fundamental question in biology is: How is variation generated? At a basic level, the vast amount of variation and biodiversity is generated through a combination of genetic and environmental processes. Traditionally these processes were treated independently, but recently fields such as evolutionary development have worked to unify our understanding of these mechanisms and to investigate how these processes interact with each other to generate variation. Developmental plasticity provides a fantastic framework for studying how genetic and environmental (GxE) interactions shape and maintain natural variation. Butterflies and their wing color patterns have long been model systems for plasticity. This dissertation seeks to address the gxe mechanisms responsible for generating color variation in the Dogface butterfly, Zerene. Zerene is comprised of only two species Z. cesonia, the Southern Dogface, and Z. eurydice, the California Dogface, that differ in their color patterns. Z. cesonia also exhibits a seasonal plastic color pattern, where Z. eurydice does not. These features make the Zerene system an excellent model for disentangling the gxe processes contributing to variation both within and between species. Using an integrative approach these studies address the role of 1.) larval host plant divergence 2.) seasonal fluctuations and 3.) hybridization on the development of wing coloration variation. The findings of these studies contribute not only to our understanding of how butterflies generate their colors, but also to the wider knowledge base on how genetics and the environment influence the generation and maintenance of biological variation.

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Chez les eucaryotes, différents types de granules à ARN sont des acteurs importants dans les mécanismes de la régulation post-transcriptionnelle de l'expression des gènes. L’irradiation aux UV induit la formation des petits granules cytoplasmiques (GUV) qui ne sont pas des processing bodies et qui semblent être une nouvelle sous classe de granules de stress. Ces granules n’ont pas la même cinétique de formation et de disparition ainsi que la taille, le nombre et la capacité de fusion que les granules de stress classiques. D’autre part, la formation de ces granules UV ne semble pas affecter le niveau de traduction, ni d’induire la réponse au stress. Toutefois, nous avons observé que l’apparition des granules coïncide avec l’arrêt de la prolifération cellulaire. En effet, dans les conditions expérimentales utilisées, la prolifération est décalée de 24 à 48 h selon la dose d’irradiation. L’ensemble de ces observations suggère fortement l'existence, d'une nouvelle sous classe de granules de stress induit par les UV, dont le rôle semble être la répression de la traduction des ARNm codant pour des facteurs importants de prolifération cellulaire.

Thesis (PhD)--Stellenbosch University, 2015. / ENGLISH ABSTRACT: This study describes: 1. The evaluation of a novel, patented thin-film, turbulent-flow Ultravioletdisinfection system as an alternative processing method to thermal pasteurisationfor the disinfection of bovine milk. 2. The microbial, biochemical and sensory characterization of bovine milk treated by heat and Ultraviolet light and then used for the commercial production of Cheddarcheese. 3. The microbial, biochemical and sensory characterization of commercial Cheddarcheese produced from bovine milk treated by heat and Ultraviolet light. / AFRIKAANSE OPSOMMING: Hierdie studie beskryf: 1. Die evaluasie van ‘n unieke, gepatenteerde dun-film, turbulente vloeiUltravioletsisteem as ‘n alternatief vir termiese pasteurisasie vir die behandeling van beesmelk. 2. Die mikrobiologiese-, biochemiese- en sensoriese karakterisasie van beesmelkbehandel met hitte en Ultravioletlig gebruik vir kommersiële produksie van Cheddar kaas. 3. Die mikrobiologiese-, biochemiese- en sensoriese karakterisasie van kommersiëleCheddarkaas vervaardig van beesmelk wat behandel is met hitte en Ultravioletlig.

Thesis--Utrecht. / Vita. Includes bibliographical references.

Diss. (sammanfattning) Göteborg : Univ. , 2009. / Härtill 4 uppsatser.

Mémoire (M.Sc.)- Université du Québec à Chicoutimi, 1975. / "Thèse présentée dans le cadre du programme UQ d'études avancées en énergie pour l'obtention du grade de la maîtrise es science (énergie)". CaQCU Document électronique également accessible en format PDF. CaQCU