A quantitative analysis of growth regulation by ppGpp in E. coli

This thesis is about a little molecule called guanosine tetraphosphate. ppGpp. Consider it the bacterial brain, at the core of the coordination and regulation of bacterial growth. For over half a century, it has haunted microbiologists as it appears involved in every aspect of microbial physiology, yet incredibly difficult to study due to its fast dynamics, chemical instability and pleiotropic effects. Like the human brain, it cannot simply be removed to show its true nature. In contrast to the pronunciation of its name, ppGpp is a rather simple molecule, and built from two of the most abundant substrates in the bacterial cell (ATP and GTP). The enzymes that make or break ppGpp are highly efficient, such that at any moment, the bacteria can decide to instantly 100-fold increase ppGpp concentrations, or virtually remove all of it. Thanks to this intelligent system, E. coli can decide to arrest growth, protecting itself against any threats, or to rapidly feast upon the sparse nutrients it may be tossed, within the order of minutes.