Physical views of bacterial cells: chromosome conformation ....
Tuesday, 12 May 2015, 16:00 - 18:00
Aula Conversi
General seminar by Pietro Cicuta
Cavendish Laboratory, University of Cambridge, UK.
Physical views of bacterial cells: chromosome conformation and size regulation in E.Coli
Bacteria are simpler than eukaryotic cells, and have served for decades as model systems to investigate various levels of biological questions. They are also of course immensely important physiologically and technologically. In this scenario E.Coli has been the model organism - and yet it is still not clear how a variety of very simple processes are carried out by the cells. Many of these open questions are not to do with specific molecular mechanisms, but are instead one level "up" in complexity. Examples go from how the chromosomes partition robustly into opposite sides of the cell, ready for division, to how the physical conformation of the chromosome at various scales affects gene expression, and to how rod-like bacteria like E.Coli "know" when to initiate cell division.
At this level, the questions have as much to do with physics as they have with the underlying specific molecular mechanisms. We will focus on just two aspects on which we have been active recently, working experimentally in our lab, and developing theory particularly with M.Cosentino Lagomarsino in Paris. The first set of results will concern the structure of the DNA in living bacteria, which we probe through the "microrheology" of individual chromosome loci. These results show a structuring of the chromosome from the origin to the terminus of replication, and also the presence of rare but anomalously large rearrangements. The second set of experiments will describe efforts at disentangling the source of size control in E.Coli; working not at the level of molecular mechanisms, but looking instead at a large dataset of single cell growth rate and cell size at division, we conclude that E.Coli cell size is regulated by neither a pure "sizer" nor "timer".