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Title: Characterisation of the cold shock response of Salmonella enterica sv. Typhimurium : genomic and genetic analysis
Author: Hutchinson, Ian Wesley
Awarding Body: University of Edinburgh
Current Institution: University of Edinburgh
Date of Award: 2005
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In the present study, the cold shock response of S. typhimurium was investigated using a small custom made DNA microarray which allowed the transcriptional profiling of cspA and its five other paralogous genes (cspB, cspC, cspD, cspE and cspH) after a temperature downshift to 10°C or 4°C from optimal growth at 37°C. Changes in low temperature expression of the six genes were monitored in exponential and stationary phase cells. Global transcriptional analysis of S. typhimurium was also performed using genomic microarrays which could measure gene expression for 97.5% of all the open reading frames in the S. typhimurium LT2 genome. This allowed expression data from other cold induced genes as well as the cspA paralogues to be examined under the same conditions used for the smaller array. The main findings from the array experiments showed that cspA and cspB appeared to be the most highly induced of the paralogues genes upon cold shock, with significant levels of transcription increase also being observed for cspC and cspE at low temperature and at 37°C. The cspH gene was confirmed as being strictly cold-induced whilst, in contrast, cspD only exhibited significant levels of induction at 37°C. The genomic microarray studies detected cold shock induction of many other genes involved in a variety of cellular activities linked to the maintenance of cell envelope integrity, DNA structure and pathogenicity, among others. The overall levels and timing of global transcription up/down regulation was observed to be influenced by growth phase and the degree to which Salmonella cells were cold-shocked, with gene induction also being detected at temperatures below the minimum for growth (4°C). these findings suggested that the cold shock response of this pathogen can still adapt the cell for survival under such conditions until a more favourable temperature arises for cell division. Extensive mutational analysis of the csp genes in S. typhimurium  indicated that two strains, harbouring only a functional cspA gene or, more interestingly, the constitutively expressed cspE gene, were fully capable of adapting the cell for growth at 10°C and for colony formation at 15°C, to a level comparable to that of the wild-type strain. A mutant strain with no functional csp genes was incapable of growth at temperatures below 20°C and exhibited a reduction in viability with extended cold incubation.  Other phenotypic tests on csp mutants seemed to indicate that CspC and CspE were capable of directly or indirectly enhancing the viability of cells to freeze/thaw treatment and that CspE may also play a role in enhancing the survival of stationary phase Salmonella cells against oxidative stress.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available