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Title: The division complex of Bacillus subtilis : assembly dynamics and regulation
Author: Gamba, Pamela
ISNI:       0000 0004 2720 1910
Awarding Body: University of Newcastle Upon Tyne
Current Institution: University of Newcastle upon Tyne
Date of Award: 2011
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Cell division in Bacillus subtilis is carried out by at least twelve proteins which assemble at midcell and form a complex known as the divisome. The main components of the divisome are known, but their precise function and the order in which they are assembled and organized within the division complex remains largely elusive. To study the dynamics and temporal hierarchy of divisome assembly in B. subtilis, we have examined the in vivo localization pattern of a set of division proteins fused to GFP, in germinating spores and vegetative cells. We have shown that the divisome assembles in two steps: the FtsZ ring assembles early and concomitantly with FtsA, ZapA and EzrA, and only after a time delay of at least 20% of the cell cycle, a second set of division proteins is recruited to midcell. Interestingly, overproduction of FtsZ advances the temporal assembly of EzrA but not of DivIVA, suggesting that a signal different to that of FtsZ polymerization drives the assembly of late divisome proteins. Surprisingly, SepF appeared to belong to the second group of division proteins. From the spore germination analysis, it emerged that FtsW is a late localizing cell division protein: by analysing its recruitment to the division site in different genetic backgrounds, we show that it is interdependent on that of PBP 2B and FtsL. Interestingly, the Z-ring appeared to disassemble upon prolonged depletion of late division proteins, suggesting an additional role for late proteins in the stabilization of the Z-ring. Surprisingly, it was found that the antibiotic tetracycline blocks cell division of an ezrA mutant carrying a functional tetracycline resistance cassette, when the strain is grown on P AB plates in the presence of the antibiotic. Overexpression of FtsL or ZapA could suppress the division defect. A screen for tetracycline insensitive suppressor mutants of ezrA was performed and two suppressor genes were identified. Their possible role in cell division was investigated.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available