The bacterial cell is a sensory system, constantly adapting to environmental fluctuations. Both the extracellular and intracellular milieux (changes in metabolite pools) are surveyed by so-called signal transduction pathways that adapt the cellular response very rapidly by adjusting various cellular parameters, the synthesis of critical cell structures (ie the cell wall in Bacillus subtilis) or even triggering large scale transcriptional programs, for example in response to starvation (ie the so-called stringent response), to the presence of polysaccharides or to govern cellular differentiation (ie heterocysts in Cyanobacteria). We are studying different types of signal transduction pathways with very distinct signaling properties. In particular, we focus on (i) the classical transcriptional regulators perceiving directly an input, (ii) the two-component systems, in which a histidine-kinase protein sensor activates a cognate response regulator, using various model systems allowing to cope with stresses (ie oxidative), nutrient availability (ie extracellular sugars), cell wall synthesis and growth, cell differentiation and motility, (iii) prophage-encoded regulators (AraC family in particular) that help their host to cope with various stress, and (iv) sRNA-mediated post transcriptional regulation involving pairing between sRNA and their mRNA targets. Last, bacteria can also adapt to new conditions by the existence of phenotypic heterogeneity, for example when lactic acid bacteria switch their metabolism depending on available resources. Using quantitative approaches directly at the single cell level, we hope to uncover core quantitative principles underlying the design of these different signaling networks aiming to show how bacteria evolve to drive optimal responses to specific cues.
Keywords: Transcriptional regulator, two-components systems, sRNA, stress response
