Anatomy of the pneumococcal nucleoid:Visualizing replication, chromosome segregation and chromosome condensation dynamics in Streptococcus pneumoniae

The pneumococcus is a bacterium that lives in the upper part of the throat behind the nose of many children and adults. In most cases it lives there harmlessly, but sometimes, it can move further into the body and cause serious illnesses as pneumonia or meningitis. Understanding how this bacterium grows could give us starting points for antibacterial drugs: if you can stop growth, you can stop the bacterium. Bacteria grow by cell division. The pneumococcus is no different: it grows in two directions, after which a wall is formed in the middle and the bacterium splits into two daughter cells. During this division cycle, the internal components of the cell need to be copied and brought to the two cell halves. In this thesis, we use several microscopy techniques to map how the DNA of the pneumococcus is copied and split into two so-called 'nucleoids' during the cell cycle. First, we benchmarked Red Fluorescent Proteins (RFPs) in the pneumococcus and developed analysis software to be able to create a map of the internal organization of the pneumococcus. Then, we followed different parts of the chromosome and proteins important for the cell cycle. We found that the correct splitting of the DNA in two nucleoids is also important for the correct placement of the septum in the middle of the cell. This shows that also in the pneumococcus, cell division and chromosome organization are connected processes.