title: Being pathogenic, plastic, and sexual while living with a nearly minimal bacterial genome.
abstract: Mycoplasmas are commonly described as the simplest self-replicating organisms, whose evolution was mainly characterized by genome downsizing with a proposed evolutionary scenario similar to that of obligate intracellular bacteria such as insect endosymbionts. Thus far, analysis of mycoplasma genomes indicates a low level of horizontal gene transfer (HGT) implying that DNA acquisition is strongly limited in these minimal bacteria. In this study, the genome of the ruminant pathogen Mycoplasma agalactiae was sequenced. Comparative genomic data and phylogenetic tree reconstruction revealed that approximately 18% of its small genome (877,438 bp) has undergone HGT with the phylogenetically distinct mycoides cluster, which is composed of significant ruminant pathogens. HGT involves genes often found as clusters, several of which encode lipoproteins that usually play an important role in mycoplasma-host interaction. A decayed form of a conjugative element also described in a member of the mycoides cluster was found in the M. agalactiae genome, suggesting that HGT may have occurred by mobilizing a related genetic element. The possibility of HGT events among other mycoplasmas was evaluated with the available sequenced genomes. Our data indicate marginal levels of HGT among Mycoplasma species except for those described above and, to a lesser extent, for those observed in between the two bird pathogens, M. gallisepticum and M. synoviae. This first description of large-scale HGT among mycoplasmas sharing the same ecological niche challenges the generally accepted evolutionary scenario in which gene loss is the main driving force of mycoplasma evolution. The latter clearly differs from that of other bacteria with small genomes, particularly obligate intracellular bacteria that are isolated within host cells. Consequently, mycoplasmas are not only able to subvert complex hosts but presumably have retained sexual competence, a trait that may prevent them from genome stasis and contribute to adaptation to new hosts.
authors.affiliation: Université Bordeaux 2, UMR1090, Villenave d'Ornon, France.
authors.forename: Pascal
authors.initials: P
authors.lastname: Sirand-Pugnet
authors.forename: Carole
authors.initials: C
authors.lastname: Lartigue
authors.forename: Marc
authors.initials: M
authors.lastname: Marenda
authors.forename: Daniel
authors.initials: D
authors.lastname: Jacob
authors.forename: Aurélien
authors.initials: A
authors.lastname: Barré
authors.forename: Valérie
authors.initials: V
authors.lastname: Barbe
authors.forename: Chantal
authors.initials: C
authors.lastname: Schenowitz
authors.forename: Sophie
authors.initials: S
authors.lastname: Mangenot
authors.forename: Arnaud
authors.initials: A
authors.lastname: Couloux
authors.forename: Beatrice
authors.initials: B
authors.lastname: Segurens
authors.forename: Antoine
authors.initials: A
authors.lastname: de Daruvar
authors.forename: Alain
authors.initials: A
authors.lastname: Blanchard
authors.forename: Christine
authors.initials: C
authors.lastname: Citti
mesh_terms: D000818:Animals; D001426:Bacterial Proteins / Q000235:genetics; D015280:DNA Restriction-Modification Enzymes; D004270:DNA, Circular / Q000235:genetics; D004275:DNA, Ribosomal / Q000235:genetics; D022761:Gene Transfer, Horizontal; D005798:Genes, Bacterial; D014644:Genetic Variation; D016680:Genome, Bacterial / Q000235:genetics / Q000502:physiology; D008074:Lipoproteins / Q000235:genetics; D008969:Molecular Sequence Data; D045644:Mycoplasma agalactiae / Q000235:genetics* / Q000502:physiology*; D009176:Mycoplasma mycoides / Q000235:genetics; D010802:Phylogeny; D012045:Regulatory Sequences, Nucleic Acid / Q000235:genetics; D012418:Ruminants / Q000382:microbiology
chemical_list: D001426:Bacterial Proteins; D015280:DNA Restriction-Modification Enzymes; D004270:DNA, Circular; D004275:DNA, Ribosomal; D008074:Lipoproteins