Osmotic stress tolerance mechanisms in Lactococcus lactis

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dc.contributor.advisor Condon, Seamus en
dc.contributor.author O'Callaghan, John
dc.date.accessioned 2014-08-13T09:35:28Z
dc.date.available 2014-08-13T09:35:28Z
dc.date.issued 1998
dc.date.submitted 1998
dc.identifier.citation O'Callaghan, J. 1998. Osmotic stress tolerance mechanisms in Lactococcus lactis. PhD Thesis, University College Cork. en
dc.identifier.uri http://hdl.handle.net/10468/1620
dc.description.abstract The response of Lactococcus lactis subsp. cremoris NCDO 712 to low water activity (aw) was investigated, both in relation to growth following moderate reductions in the aw and in terms of survival following substantial reduction of the aw with NaCI. Lc.lactis NCDO 712 was capable of growth in the presence of ≤ 4% w/v NaCI and concentrations in excess of 4% w/v were lethal to the cells. The presence of magnesium ions significantly increased the resistance of NCDO 712 to challenge with NaCI and also to challenge with high temperature or low pH. Survival of Lc.lactis NCDO 712 exposed to high NaCI concentrations was growth phase dependent and cells were most sensitive in the early exponential phase of growth. Pre-exposure to 3% w/v NaCI induced limited protection against subsequent challenge with higher NaCI concentrations. The induction was inhibited by chloramphenicol and even when induced, the response did not protect against NaCI concentrations> 10% w/v. When growing at low aw, potassium was accumulated by Lc. lactis NCDO 712 growing at low aw, if the aw was reduced by glucose or fructose, but not by NaCI. Reducing the potassium concentration of chemically defined medium from 20 to 0.5 mM) produced a substantial reduction in the growth rate, if the aw was reduced with NaCI, but not with glucose or fructose. The reduction of the growth rate correlated strongly with a reduction in the cytoplasmic potassium concentration and in cell volume. Addition of the compatible solute glycine betaine, partially reversed the inhibition of growth rate and partially restored the cell volume. The potassium transport system was characterised in cells grown in medium at both high and low aw. It appeared that a single system was present, which was induced approximately two-fold by growth at low aw. Potassium transport was assayed in vitro using cells depleted of potassium; the assay was competitively inhibited by Na+ and by the other monovalent cations NH4+, Li+, and Cs+. There was a strong correlation between the ability of strains of Lc. lactis subsp. lactis and subsp. cremoris to grow at low aw and their ability to accumulate the compatible solute glycine betaine. The Lc. lactis subsp. cremoris strains incapable of growth at NaCI concentrations> 2% w/v did not accumulate glycine betaine when growing at low aw, whereas strains capable of growth at NaCI concentrations up to 4% w/v did. A mutant, extremely sensitive to low aw was isolated from the parent strain Lc. lactis subsp. cremoris MG 1363, a plasmid free derivative of NCDO 712. The parent strain tolerated up to 4% w/v NaCI and actively accumulated glycine betaine when challenged at low aw. The mutant had lost the ability to accumulate glycine betaine and was incapable of growth at NaCI concentrations >2% w/v or the equivalent concentration of glucose. As no other compatible solute seemed capable of substitution for glycine betaine, the data suggest that the traditional; phenotypic speciation of strains on the basis of tolerance to 4% w/v NaCI can be explained as possession or lack of a glycine betaine transport system. en
dc.format.mimetype application/pdf en
dc.language English en
dc.language.iso en en
dc.publisher University College Cork en
dc.relation.uri http://library.ucc.ie/record=b1290615
dc.rights © 1998, John O'Callaghan en
dc.rights.uri http://creativecommons.org/licenses/by-nc-nd/3.0/ en
dc.subject Factors influencing survival en
dc.subject Osmotic stress tolerance en
dc.subject Glycine betaine transport system en
dc.subject Bacterial response to low water activity en
dc.subject Water activity en
dc.subject.lcsh Lactic acid bacteria en
dc.subject.lcsh Bacteria--Physiology en
dc.title Osmotic stress tolerance mechanisms in Lactococcus lactis en
dc.type Doctoral thesis en
dc.type.qualificationlevel Doctoral en
dc.type.qualificationname PhD (Science) en
dc.internal.availability Full text available en
dc.check.info No embargo required en
dc.description.version Accepted Version
dc.description.status Not peer reviewed en
dc.internal.school Microbiology en
dc.check.type No Embargo Required
dc.check.reason No embargo required en
dc.check.opt-out Not applicable en
dc.thesis.opt-out false
dc.check.embargoformat Not applicable en
ucc.workflow.supervisor cora@ucc.ie


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© 1998, John O'Callaghan Except where otherwise noted, this item's license is described as © 1998, John O'Callaghan
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