Positive feedback circuits and adaptive regulations in bacteria

The mechanisms by which bacteria adapt to changes in their environment involve transcriptional regulation in which a transcriptional regulator responds to signal(s) from the environment and regulates (positively or negatively) the expression of several genes or operons. Some of these regulators exert a positive feedback on their own expression. This is a necessary (although not sufficient) condition for the occurrence of multistationarity. One biological consequence of multistationarity may be epigenetic modifications, a hypothesis unusual to microbiologists, in spite of some well-known epigenetic modifications in bacteria. We propose here that the occurrence of mucoidy in the opportunistic pathogen Pseudomonas aeruginosa, which is currently attributed to mutations only, may also be an epigenetic modification. A theoretical approach using a generalised logical analysis lends credit to this hypothesis and suggests experiments to ascertain it.