The molecular evolution of antibiotic resistance in clinical isolates of Escherichia coli has been studied. The isolates came from a patient who was on long-term antibiotic therapy for multiple infected liver cysts. Over a period of two years seven E. coli strains were isolated from his blood during periods of septicaemia and directly from liver cysts during exploratory surgery. The liver cysts have provided a protected environmental from the antibiotic therapy the patient was receiving. The low antibiotic concentrations inside the liver cysts have allowed the bacteria to develop multiple antibiotic resistance mechanisms over time. Pulsed field gel electrophoresis patterns show that the seven isolates are closely related and are not a series of successive competitive infections. In addition, each isolate has the same basic ompC sequence that is distinct from other E. coli isolates, which suggests that they derive from the same founder population. However, the isolates differ in many characteristics including their MIC values for a range of antibiotics, auxotrophic markers, -lactamase activities, mutations in the ampC promoter sequence, mutations in gyrA and parC genes and their outer membrane permeability. The data provide strong evidence for a single focal infection expanding via parallel pathways of evolution to give a range of antibiotic resistant isolates. It is probable that the infected cysts are providing numerous protected environments that are the foci for the separate development of distinct variants.

No description available.

The spd (sporulation derepressed) mutants of Saccharomyces cerevisiae appear to have lost some of the nitrogen source repression of sporulation but remain subject to glucose repression. In media containing acetate, glycerol or pyruvate as the sole carbon source, these mutants sporulate profusely, a phenotype referred to as hypersporulation (Dawes and Calvert, 1984). This hypersporulation phenotype is also characteristic of mutants in the cAMP signal pathway which have low intracellular levels of cAMP e.g. cdc25, ras2, cdc35, yet the spdl mutants are not allelic to any of these genes. A 4.8 kb DNA sequence on a multicopy plasmid was isolated by its ability to restore growth and inhibit hypersporulation of spdl mutants on YEPG medium. Using the technique of Tn5 transposon mutagenesis, an area of 1.7 - 2.6 kb within the sequence was shown to be responsible for the above effects. The sequence hybridized to chromosome VIII indicating that it was an extragenic suppressor of the SPDI gene, which is situated on chromosome XV. Cells disrupted within the complementing region of the sequence grew more slowly than the corresponding wild-type on YEPD media. On complete media containing ethanol, glycerol or acetate as the sole carbon source, the disruptant did not grow at 30°C but grew at 26°C although at a slower rate than the corresponding wild-type. Diploids ho-mozygous for the above disruption sporulated to a much lesser extent than the corresponding wild-type cells and showed a significantly slower rate of respiration than the wild-type on both YEPD and YEPG media. DNA sequence analysis of the complementing region of the above sequence showed that it was identical to the SCH9 gene which was isolated by Toda et al., (1988).

No description available.

TlyA deletion mutants in H. pylori and B. hyodysenteriae are attenuated, suggesting that these proteins perform important roles during infection. LsaA (lawsonia surface antigen) the L. intracellularis orthologue, is expressed during infection in vitro and in vivo and suggest that this factor is involved during adherence and/or invasion of intestinal epithelial cells. The principal aim was to characterise function(s) of LsaA. Specifically the putative function as an adhesin was investigated further using a combination of biochemical and molecular approaches (including affinity purification and yeast 2-bybrid) to elucidate possible receptor(s). However, no consistent partner was evident therefore mammalian epithelial cell receptors could not be defined using this range of approaches. It is possible that LsaA’s role in adherence is adventitious – for example, it has been proposed that the TlyA family of proteins possess a regulatory role in bacterial colonisation as opposed to a direct involvement in bacterial adherence. The existence of two conserved putative functional domains S4RNA binding and methyltransferase motifs have been noted in all members of the TlyA family examined to date. These domains are found separately in several protein families known to be involved in gene regulation. Since no system has been developed for mutating genes in L. intracellularis the proteome of a TlyA deletion mutant of H. pylori was compared to its parent to further this potentially new and interesting function of TlyA family proteins. Notably, flagellin B and catalase were absent in the tlyA mutant. Since deletion of tlyA corresponds with changes in expression of several H. pylori genes, it can be concluded that reduced colonisation of H. pylori tlyA mutant is likely to be as a result of effects on expression of virulence genes rather than a direct role in adherence.

The major aim of this project has been the study of the action of mutagens upon yeast cells at discrete stages of the cell cycle. To provide a sufficiently large population of cells at appropriate stages of the mitotic division cycle it has been necessary to develop the use of the zonal rotor for this purpose. After treatment with a range of physical and chemical mutagens cyclic variations were observed in the induction of a number of genetic end points i.e. mitotic recombination (both reciprocal and non- reciprocal), mutation (both base substitution and frameshift) and mitotic aneuploidy. In general, physical mutagens were found to give maximum induction of these genetic end points in GI, whereas the chemical mutagens predominantly had their maximal effect upon S phase cells. Control experiments have indicated that the observed GI sensitivity of yeast cells to radiation cannot be attributed to cell size differences (cytoplasmic shielding). However the budding resistance of S and G2 cells required a functional RAD 50 gene together with the close association of sister chromatids. A sister strand exchange post-replication repair mechanism has been proposed to account for budding repair of radiation damage. The increased sensitivity of S phase cells to chemical mutagens may occur due to differential uptake. Larger amounts of labelled EMS were taken into yeast cells during S phase, when possibly the DNA of the cells was more exposed. The observed association between the maximum induction of lethality and the induction of the various genetic end points has led to the conclusion that similar DNA lesions can lead to different genetic consequences during the cell cycle. However, the situation may be complicated by data which shows that caffeine reduces gene conversion whilst increasing base substitution mutation in S phase after nitrous acid exposure. This indicates that error-prone repair and mitotic gene conversion may compete for similar DNA lesions. Indirect evidence has also been presented which indicates that error-prone repair in yeast may be constitutive whereas error-free repair may be inducible. Cell populations of stationary and G1 phase cells were found to be distinguishable on the basis of their radiosensitivity. This has been taken as support for the hypothesis that stationary phase cells are outside the mitotic cell cycle in CO phase.

This project investigates the factors which may affect the response of yeast cells to potential mutagens and thus to optimise their response. The problem was approached from four main angles as follows: i) permeability - rendering the cells more permeable either by pre-treatment with selected chemicals or by selecting clones with cell wall defects; ii) repair capacity - preventing adequate repair of damaged DNA either by post-treatment with repair inhibitors or by using strains with defective repair genes; iii) genetic background - looking at reversion in the same gene but in a different genetic background or different genes in the same background; iv) treatment conditions - treating cells in buffer or broth, with or without exogenous activation, at 28 C or 37 C. The general conclusions which may be drawn from these studies are: a) most chemical mutagens are able to enter the yeast cells in sufficient quantities to cause damage to the DNA without pre-treating the cells to increase their permeability; b) the repair capacity of a cell is a very important factor in its response to a mutagen and if this capacity is greatly impaired, then the chances of survival of the cell after treatment with a mutagen are greatly reduced; c) the genetic background of a cell and the marker under consideration can affect the response of the cell to a mutagen; d) the conditions under which yeast cells are exposed to mutagens affect both the response of the yeast cells and the effectiveness of the mutagen itself. As for optimising the response of the yeast cells to mutagens this can only be done by gathering together all the information already known about the compound under study, and any related compounds, and analysing this data to discover what treatment conditions should be used and possibly what test.

No description available.

Candida albicans is an opportunistic fungal pathogen of humans causing superficial mucosal infections and more serious systemic infections in immunocompromised individuals. It is found in both yeast and hyphal forms at sites of infection. In the human body levels of iron are extremely low, and an invading organism needs a way of sequestering iron. In C. albicans there is a high affinity iron uptake system in which iron is first reduced to the soluble ferrous form by ferric reductases. Reduced iron is then taken up into the cell by a complex of a multicopper oxidase protein with an iron transport protein. Multicopper oxidase proteins require copper to function and so high affinity iron and copper uptake is inextricably linked. It has previously been demonstrated that CaFre10p is the major cell surface ferric and cupric reductase. It is shown here that CaFre7p also makes a significant contribution to cell surface ferric and cupric reductase activity. However, whereas CaFRE10 is regulated in response to iron levels, CaFRE7 is regulated in a copper responsive manner. The CaFRE10 gene is regulated by the GATA-type transcriptional repressor Sfu1p and CaFRE7 is not. We show that in a mutant containing a deletion of SFU1 the expression of the major iron transport protein CaFTR1 is increased and there is a corresponding increase in radioactive iron uptake. It is also shown here for the first time that expression of CaFRE10 and CaFRE7 is lower in hyphae compared to yeast and that this leads to a corresponding decrease in cell surface ferric, but not cupric reductase activity. This shows for the first time that two important virulence determinants, the acquisition of iron and the morphological form of C. albicans, are linked.

For the foodborne enteric pathogen Campylobacter jejuni, regulation of iron homeostasis is tightly controlled by the ferric uptake regulator Fur. Fur regulates iron-responsive gene expression by binding to the Fur box sequence and a 19 bp Fur box is positioned within the promoter region of the outer membrane haem receptor gene chuA. The fumarase fumC Fur box-like sequence shows three mismatches to the consensus sequence and this variation is predicted to be key to the contrasting iron regulation and Fur-Fur box binding affinity between chuA and fumC. The aims of this study were to determine the functionally important bases in the C. jejuni Fur box that are essential for Fur-Fur box interaction and to assess the interplay of iron and oxygen in the modulation of fumC expression. Site-directed mutagenesis of the 1st, 7th, 10th, 13th and 19th positions was carried out for the chuA and fumC Fur boxes and their interaction with Fur was determined in vitro and in vivo. Two Fur dimers were determined to bind to the Fur box, and although the 1st, 7th, 13th and 19th positions were found to facilitate the interaction of Fur with the Fur box, the architecture of the promoter region is likely to play a more significant role in Fur regulation. fumC encodes the only fumarase in C. jejuni and it is essential for cell growth and for maintaining a functional tricarboxylic acid cycle. Further characterisation of chuA and fumC expression in response to iron and oxygen indicated that both genes are controlled by Fur as well as the peroxide response regulator PerR, and the RacR-RacS two-component system. These observations illustrate the necessity for C. jejuni to cooperatively regulate essential gene expressions using its rather limited set of regulators thus allowing it to adapt to various conditions encountered during transmission and colonisation.