Rhizobium meliloti mutants defective in C₄-dicarboxylic acid transport (Dct⁻) were previously isolated by Tn5 mutagenesis, and divided into two groups based on complementation of Dct- with cosmid clones. In this work further characterization was carried out on the two loci. Group I mutants were found to be defective in dicarboxylate transport (Dct⁻), nitrate utilization, and symbiotic nitrogen fixation. Subcloning and complementation work confined the Group I mutations to a 3.5 kbp BamHI-EcoRI fragment containing the ntrA gene. Group V mutants were defective in dicarboxylate transport and demonstrated varying levels of nitrogen fixation. Complementation and site-directed Tn5 mutagenesis revealed three transcriptional units, corresponding to dctA,
dctB, and dctD, localized within a 6 kbp HindIII fragment. The use of dctA::TnphoA fusions determined the expression of dctA to be ntrA, dctB, and dctD dependent. Dct+ revertants of dctB and dctD mutants were selected which carried second-site mutations responsible for restoring the Dct⁺ phenotype. / Thesis / Master of Science (MS)
| Identifer | oai:union.ndltd.org:mcmaster.ca/oai:macsphere.mcmaster.ca:11375/22936 |
| Date | 01 1900 |
| Creators | Yarosh, Oksana |
| Contributors | Finan, T. M., Biology |
| Source Sets | McMaster University |
| Language | English |
| Detected Language | English |
| Type | Thesis |
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