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PLoS Genetics 5, 10 (2009) e1000677
Life on arginine for Mycoplasma hominis: clues from its minimal genome and comparison with other human urogenital mycoplasmas.
Sabine Pereyre, Pascal Sirand-Pugnet 1, Laure Beven 2, Alain Charron, Hélène Renaudin, Aurélien Barré 3, Philippe Avenaud, Daniel Jacob 3, Arnaud Couloux 4, Valérie Barbe, Antoine De Daruvar 3, 5, Alain Blanchard 6, Cécile Bébéar ( ) 7

Mycoplasma hominis is an opportunistic human mycoplasma. Two other pathogenic human species, M. genitalium and Ureaplasma parvum, reside within the same natural niche as M. hominis: the urogenital tract. These three species have overlapping, but distinct, pathogenic roles. They have minimal genomes and, thus, reduced metabolic capabilities characterized by distinct energy-generating pathways. Analysis of the M. hominis PG21 genome sequence revealed that it is the second smallest genome among self-replicating free living organisms (665,445 bp, 537 coding sequences (CDSs)). Five clusters of genes were predicted to have undergone horizontal gene transfer (HGT) between M. hominis and the phylogenetically distant U. parvum species. We reconstructed M. hominis metabolic pathways from the predicted genes, with particular emphasis on energy-generating pathways. The Embden-Meyerhoff-Parnas pathway was incomplete, with a single enzyme absent. We identified the three proteins constituting the arginine dihydrolase pathway. This pathway was found essential to promote growth in vivo. The predicted presence of dimethylarginine dimethylaminohydrolase suggested that arginine catabolism is more complex than initially described. This enzyme may have been acquired by HGT from non-mollicute bacteria. Comparison of the three minimal mollicute genomes showed that 247 CDSs were common to all three genomes, whereas 220 CDSs were specific to M. hominis, 172 CDSs were specific to M. genitalium, and 280 CDSs were specific to U. parvum. Within these species-specific genes, two major sets of genes could be identified: one including genes involved in various energy-generating pathways, depending on the energy source used (glucose, urea, or arginine) and another involved in cytadherence and virulence. Therefore, a minimal mycoplasma cell, not including cytadherence and virulence-related genes, could be envisaged containing a core genome (247 genes), plus a set of genes required for providing energy. For M. hominis, this set would include 247+9 genes, resulting in a theoretical minimal genome of 256 genes.
1 :  Génomique, développement et pouvoir pathogène (GD2P)
Institut national de la recherche agronomique (INRA) : UR1090 – Université Victor Segalen - Bordeaux II
2 :  Génie Enzymatique et Cellulaire (GEC)
CNRS : UMR6022 – Université de Technologie de Compiègne – Université de Picardie Jules Verne
3 :  Centre de Bioinformatique de Bordeaux (CBIB)
4 :  Genoscope-Centre national de séquençage (GENOSCOPE)
5 :  Laboratoire Bordelais de Recherche en Informatique (LaBRI)
CNRS : UMR5800 – Université Sciences et Technologies - Bordeaux I – École Nationale Supérieure d'Électronique, Informatique et Radiocommunications de Bordeaux (ENSEIRB) – Université Victor Segalen - Bordeaux II
6 :  Laboratoire Astrophysique de Toulouse-Tarbes (LATT)
CNRS : UMR5572 – INSU – Observatoire Midi-Pyrénées – Université Paul Sabatier (UPS) - Toulouse III
7 :  Service de Bactériologie
Hôpital Pellegrin-Tripode
Sciences du Vivant/Bio-Informatique, Biologie Systémique