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Title: Rhodopseudomonas palustris : a model of bacterial differentiation
Author: Westmacott, Donald
ISNI:       0000 0001 3566 2328
Awarding Body: University of Warwick
Current Institution: University of Warwick
Date of Award: 1976
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Differentiation in the budding photosynthetic bacterium Rhodopseudomonas palustris was studied both in its own right and in the context of other comparable bacteria; particularly R. acidophila and Rhodomicrobium vannielii. Together, these three Rhodospirillaceae present a gradient of morphogenetic complexity ideally suited to differentiation studies. Semi-defined conditions were determined which gave consistent morphology and fast growth rates. Heterogeneous cultures of R. palustris were then synchronised by selecting swarmer cells by sucrose gradient sedimentation. Morphology and ultrastructure of the cell division cycle exhibited by R. palustria were examined in some detail and compared with R. acidophila. Both organisms exhibited differentiation at the sub-cellular level and by dividing to give two dissimilar cells. The distribution of cell types, stepwise doublings, particle volume distributions, optical density changes, cell motility, protein and DNA synthesis and probably also RNA synthesis were all examined during synchronous growth of R. palustris. Penicillin treatment showed that cell growth was by polar, unidirectional synthesis of wall material, Nalidixic acid, which inhibits DNA replication, modified the cell development by inhibiting cell division and giving rise to abnormal cell elongation. Studies with nalidixic acid also confirmed that there was periodic DNA synthesis during the normal cell cycle. Observations on the location of cell division in elongated cells after removal of the nalidixic acid, considered alongside the polar unidirectional mode of cell growth, allowed a model correlating chromosome replication and cell envelope growth to be proposed. Some preliminary investigations were made of mutants of R. palustris. Temperature-sensitive mutants were obtained, but these did not appear to be blocked at any particular stage of development. A phage specific for one strain of H. palustris was investigated and appeared to be temperature-sensitive in some step of its growth cycle. This might permit its use for transduction. Both temperature-sensitive mutants and a method of genetic transfer were considered invaluable for further studies of the control of R. palustris differentiation.
Supervisor: Not available Sponsor: Medical Research Council
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: QH Natural history ; QR Microbiology