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Title: Regulation of compatible solute accumulation in enteric bacteria by osmotic stress
Author: Koo, S.-P.
Awarding Body: University of Aberdeen
Current Institution: University of Aberdeen
Date of Award: 1993
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Betaine, the predominant compatible solute of bacterial cells, is transported by the ProP and ProU transport systems of E.coli and S.typhimurium under conditions of osmotic stress. Transport via these systems is modulated both at the level of gene expression and the level of activity by osmotic pressure of the medium. The primary aim of this study was to elucidate the mechanism(s) of regulation of betaine accumulation by osmotic pressure. The second objective was to establish a quantitative model of osmoadaptation in enteric bacteria with a view to predicting the survival and growth of the organisms under conditions of osmotic stress. Growth simulation by betaine strongly correlated with intracellular betaine concentration over a limited range. There was an upper limit of growth simulation achieved by the accumulation of betaine. Generally, the ProP and ProU transport systems could substitute for each other in effecting betaine accumulation. A betaine concentration as low as 100nM was able to confer osmoprotection but the growth stimulation was dependent upon the activity of the ProU system. Analysis of steady-state betaine accumulation in S.typhimurium indicated that betaine accumulation is a stress-regulated response. However, this regulation did not lie in the uptake system since they were not feedback regulated. Physiological evidence obtained from experiments using sulphydryl reagents indicated the presence of a novel betaine efflux system, which was proposed to be the site of regulation. Genetic evidence for the existence of this efflux system was sought by the isolation of betaine efflux mutants. A screening procedure was developed to detect the leak of betaine and two mutants were isolated. Analysis of the mutation in one of the mutants, however, indicated that it is located in the proP gene. Future strategies for the isolation of betaine efflux mutants are discussed.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available