Use this URL to cite or link to this record in EThOS:
Title: Genetic and physiological studies on Rhizobium trifolii
Author: Ronson, Clive William
ISNI:       0000 0001 3534 7272
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1979
Availability of Full Text:
Access from EThOS:
Access from Institution:
The aim of this study was to investigate the Rhizobium - legume symbiosis by use of mutants of R. trifolii. Attempts to demonstrate R68-45 mediated chromosomal recombination In R. trifolii were unsuccessful. However, the pathways and regulation of nitrogen and carbon metabolism in R. trifolii were studied. Rhizobium trlfolii assimilated ammonia solely by the glutamine synthetase/glutamate synthase (GS/GOGAT) pathway. Neither strain W19, which lacked GOGAT, nor pyruvate-carboxylase mutants of strain 7000 could utilize glutamate-yielding amino-acids to satisfy their growth requirements. It was proposed that GS regulated the synthesis of the required catabolic enzymes, and that GS was regulated by the intracellular 2-oxoglutarate to glutamine ratio. The Embden-Meyerhof-Parnas pathway was not found in R, trifolii. By use of mutants, it was shown that glucokinase (glk) was required for glucose phosphorylation in wild-type bacteria and the Entner-Doudoroff pathway for catabolism of all six-carbon sugars except galactose. Pyruvate carboxylase was the physiologically important anaplerotlc enzyme. The effective symbiotic properties of the carbohydrate-negative mutants showed that hexoses were not the energy-substrates received by the bacteroids. The glk mutants did not grow on glucose, maltose, celloblose, trehalose, sucrose, lactose or dulcitol. The syntheses of the lactose and dulcitol transport systems were hypersensitive to repression by a second carbon source in the glk mutants. A model was proposed to explain the pleiotropic defect. The catabolism of glucose to at least glucose 6-phosphate was required for the regulation of those catabolic systems which were sensitive to catabolite repression by glucose. The utilization of the polyols sensitive to catabolite repression was inhibited by 2-deoxyglucose in both wild-type and glk strains. It was proposed that the regulation of catabolic enzyme synthesis In R. trifolii was manifested mainly at the level of Inducer exclusion.
Supervisor: Not available Sponsor: National Research Advisory Council, New Zealand
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH Natural history ; QK Botany ; QP Physiology ; QR Microbiology