Curing clover rhizobia of plasmids and defining the ecological and physiological functions of the plasmids /
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| Other Authors: | , , |
| Format: | Thesis Book |
| Language: | English |
| Published: |
1990.
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| Subjects: | |
| Online Access: | Link to OAKTrust copy |
| Abstract: | This study was undertaken to define ecological and physiological functions of plasmids in three strains of Rhizobium leguminosarum bv. trifolii. Strains were characterized with respect to the number and size of resident plasmids. Plasmid profiles indicated the presence of three, four and five plasmids in strains W14-2, Wll-9 and W8-7, respectively. Only one plasmid per strain (pRtrW14-2d, pRtrW11-9a and pRtrW8-7c) hybridized with a probe pCHk12 carrying nif genes and therefore was termed pSym. The other plasmids were classified as cryptic because of their unknown functions. Curing of plasmids was accomplished by insertion of Tn5-SacB genes into plasmids and incubation of transconjugants either at 28°C or higher temperature (39°C to 44°C) on 5% sucrose plates. Many cured derivatives were selected simply by incubating transconjugants at 28°C and curing was independent of the size of the plasmid. Other plasmids were cured only with high temperatures. In two cases, pRtrWll-9c and pRtrW8-7d, plasmids were not eliminated from the cell. Evaluation of the phenotypic expression of cured derivatives in sterile soil subjected to low moisture (-1.5 MPa/28°C) or high temperature (38 to 42°C/-0.03 MPa) indicated that loss of plasmids affected survival of the bacteria. Low soil moisture reduced survival of some derivatives and was observed to be strain dependent. Elimination of plasmids pRtrW14-2a and pRtrW8-7bc increased survival of derivatives under low soil moisture. High temperature was more detrimental than moisture stress for derivatives W8- 7e and W8-7bc. In contrast, curing of plasmids did not interfere with ability of derivatives of strains W14-2 and W11-9 to grow at pH values in the range of 4.5 to 6.0. Some cured derivatives lost the ability to utilize simple sugars, dicarboxylic acids and catechol. It was determined that plasmids pRtrW14-2a, pRtrWll-9b and pRtrW8-7b carried genes for utilization of more than one carbon source. Additionally, elimination of plasmid a in strain W14-2 and plasmid b in strain W8-7 impaired motility of the cured bacteria. |
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| Item Description: | Typescript (photocopy). Vita. "Major subject: Soil Science." |
| Physical Description: | xii, 155 leaves : illustrations ; 29 cm |
| Bibliography: | Includes bibliographical references. |