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

• Published in: Molecular microbiology Vol. 76; no. 3; pp. 634 - 647
• Main Authors: Moriya, S, Rashid, R.A, Rodrigues, C.D. Andrade, Harry, E.J
• Format: Journal Article
• Language: English
• Published: Oxford, UK Oxford, UK : Blackwell Publishing Ltd 01-05-2010; Blackwell Publishing Ltd; Blackwell
• Subjects: Bacillus subtilis; Bacillus subtilis - cytology; Bacillus subtilis - genetics; Bacillus subtilis - metabolism; Bacteria; Bacterial Proteins; Bacteriology; Biological and medical sciences; Cell Division; Cell Nucleolus - genetics; Cell Nucleolus - metabolism; Deoxyribonucleic acid; DNA; DNA Replication; Fundamental and applied biological sciences. Psychology; Intranuclear Inclusion Bodies - genetics; Intranuclear Inclusion Bodies - metabolism; Microbiology; Miscellaneous; Morphology; Bacteria; Replication; Early stage; Bacillales; Bacillaceae; Bacillus subtilis
• ISSN: 0950-382X; 1365-2958
• DOI: 10.1111/j.1365-2958.2010.07102.x

Although division site positioning in rod-shaped bacteria is generally believed to occur through the combined 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 inhibiting the early stages of DNA replication, leading up to assembly of the replisome at oriC, 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 morphology (lowering DNA concentration at midcell), whereas acentral Z rings form beside a single-lobed nucleoid. Remarkably however, when the DnaB replication 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.