title: Phylogenomic analysis supports the ancestral presence of LPS-outer membranes in the Firmicutes.
abstract: One of the major unanswered questions in evolutionary biology is when and how the transition between diderm (two membranes) and monoderm (one membrane) cell envelopes occurred in Bacteria. The Negativicutes and the Halanaerobiales belong to the classically monoderm Firmicutes, but possess outer membranes with lipopolysaccharide (LPS-OM). Here, we show that they form two phylogenetically distinct lineages, each close to different monoderm relatives. In contrast, their core LPS biosynthesis enzymes were inherited vertically, as in the majority of bacterial phyla. Finally, annotation of key OM systems in the Halanaerobiales and the Negativicutes shows a puzzling combination of monoderm and diderm features. Together, these results support the hypothesis that the LPS-OMs of Negativicutes and Halanaerobiales are remnants of an ancient diderm cell envelope that was present in the ancestor of the Firmicutes, and that the monoderm phenotype in this phylum is a derived character that arose multiple times independently through OM loss.
authors: Unité de Biologie Moléculaire du Gène chez les Extrêmophiles, Département de Microbiologie, Institut Pasteur, Paris, France.
authors: Luisa Cs
authors: LC
authors: Antunes
authors: Unité de Biologie Moléculaire du Gène chez les Extrêmophiles, Département de Microbiologie, Institut Pasteur, Paris, France.
authors: Daniel
authors: D
authors: Poppleton
authors: Plant Development and Electron Microscopy, Department of Biology I, Biocenter LMU, Munich, Germany.
authors: Andreas
authors: A
authors: Klingl
authors: Bioinformatics and Biostatistics Hub, Institut Pasteur, Paris, France.
authors: Alexis
authors: A
authors: Criscuolo
authors: Laboratoire Pathogenèse des Bactéries Anaérobies, Département de Microbiologie, Institut Pasteur, Paris.
authors: Bruno
authors: B
authors: Dupuy
authors: Laboratoire de Biométrie et Biologie Évolutive, University Lyon I, Villeurbanne, France.
authors: Céline
authors: C
authors: Brochier-Armanet
authors: Unité de Génétique des Biofilms, Département de Microbiologie, Institut Pasteur, Paris, France.
authors: Christophe
authors: C
authors: Beloin
authors: Unité de Biologie Moléculaire du Gène chez les Extrêmophiles, Département de Microbiologie, Institut Pasteur, Paris, France.
authors: Simonetta
authors: 0000-0002-7662-021X
authors: S
authors: Gribaldo
mesh_terms: D053898:Biosynthetic Pathways / Q000235:genetics*; D002462:Cell Membrane / Q000235:genetics*; D019143:Evolution, Molecular; D000068536:Bacillota / Q000166:cytology / Q000235:genetics*; D008070:Lipopolysaccharides / Q000235:genetics*; D010802:Phylogeny
chemical_list: D008070:Lipopolysaccharides
keywords: Firmicutes; Halanaerobiales; Negativicutes; cell biology; evolutionary biology; genomics; none