The dynamic role of the conserved WhiA and MinD proteins in chromosome segregation, fatty acid metabolism and cell division in Bacillus subtilis

This thesis presents several studies, using genetics, cell biology techniques, transcriptomics and metabolomics, to investigate the function of cell division proteins. The protein WhiA is present in most Gram-positive bacteria, binds to DNA and induces expression of cell division genes. B. subtilis WhiA is not a transcription factor and its functional role is unknown. Here, it was found that the whiA mutants show an increased space between their nucleoids. The deletion of whiA is synthetic lethal when DNA replication and segregation regulators are absent. However, WhiA does not affect replication initiation. The whiA mutants are highly sensitive for DNA damaging agents. The results indicate that WhiA has two separate roles in cell division and chromosome segregation. The whiA gene is part of an operon and flanked by two metabolic genes, therefore, B. subtilis WhiA might play a role in carbon metabolism. A metabolomics approach was followed and it was found that WhiA does not participate in carbon catabolite regulation, but affects fatty acid composition of the membrane. The B. subtilis Min system form a static gradient decreasing towards midcell, and prevent formation of minicells by blocking FtsZ polymerization close to cell poles. Here, it was found that the dynamic cycling between monomer and dimer is essential for a MinD gradient, and that the interaction with MinJ requires dimerization. The monomeric and dimeric forms of MinD have comparable membrane affinities. The results show that increasing the MinD membrane affinity strongly reduces the formation of a gradient and affects interaction with MinC