Influence of the nucleoid and the early stages of DNA replication on positioning the division site in Bacillus subtilis

Blackwell Publishing Ltd
Publication Type:
Journal Article
Molecular Microbiology, 2010, 76 (3), pp. 634 - 647
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Although division site positioning in rod~shaped bac~ teria is generally believed to occur through the com~ bined effect of nucleoid occlusion and the Min system, several lines of evidence suggest the existence of additional mechanisms. Studies using outgrown spores of Bacillus subtilis have shown that inhi·biting ~ the early stages of DNA replication, leading up to . assembly of the replisome at orie, influences Z ring positioning. Here we examine whether Z ring formation at midcell under various conditions of DNA replication inhibition is solely the result of relief of nucleoid occlusion. We show that midcell Z rings form preferentially over unreplicated nucleoids that have a bilobed mor~ phology (lowering DNA concentration at midcell), whereas acentral Z rings form beside a single~lobed nucleoid. Remarkably however, when the Dna8 repli~ cation initiation protein is inactivated midcell Z rings never form over bilobed nucleoids. Relieving nucleoid occlusion by deleting noc increased midcell Z ring frequency for all situations of DNA replication inhibItion, however not to the same extent, with the DnaB~ inactivated strain having the lowest frequency of midcell Z rings. We propose an additional mechanism for Z ring positioning in which the division site becomes increasingly potentiated for Z ring formation as initiation of replication is progressively completed.
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