The putative calcium-binding protein Asp24 is required for acid resistance and survival of Brucella abortus /
B.abortus is a gram-negative, facultative intracellular
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| Format: | Thesis Book |
| Language: | English |
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[Place of publication not identified] :
[publisher not identified] ;
1997.
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| Online Access: | http://proxy.library.tamu.edu/login?url=http://proquest.umi.com/pqdweb?did=739887951&sid=1&Fmt=2&clientId=2945&RQT=309&VName=PQD |
| Summary: | B.abortus is a gram-negative, facultative intracellular bacterium that replicates and survives within host macrophages. Evidence suggests that brucellae survive in phagocytes by inhibiting phagolysosomal fusion, and resisting killing within the phagolysosome. However, the molecular mechanisms of Brucella that protect against antimicrobial factors within host macrophages have not been clearly established. In an effort to define the mechanisms employed by B. abortus to resist intracellular killing, gene expression following phagocytosis was examined. Synthesis of a 24-kDa protein of B. abortus, designated Asp24, was observed to increase. Expression of asp24 was also shown to respond to reduced pH and calcium chelation. A reduction in intracellular calcium in B. abortus was shown to occur following exposure to reduced pH such as occurs within the phagosome of infected cells. Thus, expression of asp24 may represent an attempt to sequester calcium under these conditions. The deduced amino acid sequence of Asp24 reveals potential calcium-binding motifs and Asp24 exhibits a calcium-dependent shift in mobility, suggesting that Asp24 is a putative calcium-binding protein. The mouse model was employed to determine the role of Asp24 in the growth and virulence of B. abortus. Insertion mutants deficient in asp24 expression CBP1 exhibited a 100-fold reduction in colony forming units in the spleens of infected mice at 6 weeks postinoculation, and expression of asp24 from the plasmid pBBRasp24 restored the wild-type phenotype. This result is consistent with the survival of both organisms during adaptive acid tolerance response, but not with that following direct exposure to acid shock without preadaptation. This result may be best explained by the absence of sustained exposure to acidic environments or other inducing conditions in the mouse model. The asp24 mutants exhibited increased acid sensitivity, and failed to mount an acid tolerance response in vitro. This correlates with the decreased survival of asp24 mutant in vivo and is presumed to be the basis for its attenuation. These results suggest that Asp24 plays an important role in developing acid tolerance response. The mechanisms involved and the significance to late-stage survival will be discussed. |
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| Item Description: | Vita. "Major Subject: Biology". In title, numerals are used. |
| Physical Description: | xii, 131 leaves : illustrations ; 28 cm. Issued also on microfiche from University Microfilms Inc. |
| Bibliography: | Includes bibliographical references: pages 110-130. |