Ronson, Clive William (1979) Genetic and physiological studies on Rhizobium trifolii. PhD thesis, University of Warwick.

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Abstract

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.

Item Type:	Thesis or Dissertation (PhD)
Subjects:	Q Science > QH Natural history Q Science > QK Botany Q Science > QP Physiology Q Science > QR Microbiology
Library of Congress Subject Headings (LCSH):	Rhizobium, Legumes, Symbiosis, Carbohydrates -- Metabolism, Nitrogen -- Fixation
Official Date:	January 1979
Dates:	Date Event January 1979 Submitted
Institution:	University of Warwick
Theses Department:	Department of Biological Sciences
Thesis Type:	PhD
Publication Status:	Unpublished
Supervisor(s)/Advisor:	Primrose, S. B.
Sponsors:	New Zealand. National Research Advisory Council
Extent:	xiv, [260] leaves
Language:	eng

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