The envelope is one of the oldest and most important cell components, and the first interface between an organism and its environment. Bacteria are known to have either one membrane (Gram-positives or monoderms) or two membranes (Gram-negatives or diderms). How the transition between these two radically different envelopes occurred has been one of the most intriguing mysteries in evolutionary biology. We have recently tackled this question by merging large-scale phylogenomics approaches with the development of a new experimental diderm model belonging to the classical monoderm Firmicutes. Our results shake longstanding assumptions and show the power of continuous exploration of ever larger fractions of microbial diversity.
Simonetta Gribaldo is an Evolutionary Microbiologist. Her research interests focus on ancient evolution. By applying phylogenomics approaches, Simonetta investigates major evolutionary transitions on the Tree of Life. Her work has contributed to establishing robust reference organismal phylogenies, in particular for the Archaea, and provided a novel view on the diversity and evolutionary history of the most enigmatic of the three domains. Recently, she has proposed a novel topology for the universal tree, with an original root of the Archaea and the possibility of a methanogenic ancestor. Simonetta completed her PhD in 2001 at « La Sapienza » University in Rome, Italy, then moved to France for her postdoctoral studies. She obtained a permanent position in 2005 at the Institut Pasteur, Paris, where she is currently Research Director and head of the team « Microbial Phylogenomics ».