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Title: Structure of the R. vannielii genome
Author: Potts, Linda Elizabeth
ISNI:       0000 0001 3497 2543
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1980
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The control of cellular morphogenesis and differentiation at the molecular level in Rhodomicrobium vannlelii is investigated by biochemical and genetic analysis. Chemical characterization indicates that the R.vannlelll genome is 2.19 x 109 daltons, and is made up of 95 per cent unique DNA sequence. Five per cent of the DNA consists of short inverted repeat sequences, 400 bp in length. No extrachromoscmal DNA is detectable. The DNA from each of the cellular expressions in R.vannielil does not show any major differences in sequence composition. Kinetic analysis of nucleic acid synthesis during the obligate differentiation of the swarm cell shows a 'lag' or maturation period prior to the onset of DNA replication, whereas no lag occurs in RNA synthesis. The initiation of DNA replication during swarm cell differentiation occurs towards the completion of stalk synthesis. Studies with the protein synthesis inhibitor chloramphenicol during swarm cell differentiation demonstrate a requirement for protein synthesis in the initiation, but not the elongation step of DNA replication. Nalidixic acid inhibits DNA synthesis in the swarm cell, and although a new daughter cell is produced, cell division does not occur. This implies that chromosome replication and cell division cure directly linked in a 'dependent pathway' of events. Daughter cell synthesis is under the control of the mother cell genome, the daughter cell genome becoming metabolically active just prior to cell division. Further 'cells' produced in nalidixic acid-treated cultures show gross cellular distortion and no stalk formation. The development of a genetic system for R.vannielll is discussed. The promiscuous plasmid R.68.45 is transferred by conjugation from E.coll to R.vannlelll, where it expresses only one of three plasmid-bome antibiotic resistances, but may be maintained intact in the bacterium. This plasmid may now be used in mapping the R.vannielll chromosome. Analysis of the R.vannlelli genome by restriction enzyme cleavage is described. Restriction fragments containing the coding sequences for 16s rRNA and 23s rRNA are Identified by 'Southern' hybridization, and their sizes estimated. Attempts to locate the origin of replication on a single restriction fragment are discussed. Preliminary data on the physiology of nitrogen fixation in R.vannlelli shows that the enzyme system is inducible. The potential of this organism as a model system for further study on the molecular biology of microbial morphogenesis and differentiation is discussed.
Supervisor: Not available Sponsor: Science Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH426 Genetics ; QR Microbiology