Transcriptome analysis of Yersinia pestis in human plasma: an approach for discovering bacterial genes involved in septicaemic plague

1 Yersinia Research Unit, Institut Pasteur, 28 rue du Dr. Roux, F-75724 Paris cedex 15, France 2 Institut Pasteur de Lille, Lille, France 3 Plate-Forme 4, Institut Pasteur, Paris, France 4 Plate-Forme 2, Institut Pasteur, Paris, France 5 Génoscope, Evry, France Correspondence Sylvie Chauvaux chauvaux{at}pasteur.fr Yersinia pestis is the aetiologic agent of plague. Without appropriate treatment, the pathogen rapidly causes septicaemia, the terminal and fatal phase of the disease. In order to identify bacterial genes which are essential during septicaemic plague in humans, we performed a transcriptome analysis on the fully virulent Y. pestis CO92 strain grown in either decomplemented human plasma or Luria–Bertani medium, incubated at either 28 or 37 °C and harvested at either the mid-exponential or the stationary growth phase. Y. pestis genes involved in 12 iron-acquisition systems and one iron-storage system ( bfr , bfd ) were specifically induced in human plasma. Of these, the ybt and tonB genes (encoding the yersiniabactin siderophore virulence factor and the siderophore transporter, respectively) were induced at 37 °C, i.e. under conditions mimicking the mammalian environment. Growth in human plasma also upregulated genes involved in the synthesis of five fimbrial-like structures (including the Psa virulence factor), and in purine/pyrimidine metabolism (the nrd genes). Genes known to play a role in the virulence of several bacterial pathogens (such as those encoding the Lpp lipoprotein and non-iron metal-uptake proteins) were induced in human plasma, during either the exponential or the stationary phase. Finally, 120 genes encoding proteins of unknown function were upregulated in human plasma. Eleven of these genes were specifically transcribed at 37 °C and may thus represent new virulence factors that are important during the septicaemic phase of human plague. Abbreviations: QRT-PCR, quantitative real-time PCR A supplementary figure showing QRT-PCR confirmation of transcriptome results, and four supplementary tables listing the fold-changes due to medium, temperature and growth phase, and the 30 most highly expressed Y. pestis chromosomal genes in human plasma, are available with the online version of this paper. The array data discussed in this publication have been deposited in the Genoscript database ( http://genoscript.pasteur.fr ) and are accessible as experiment ‘Human plasma Y. Pestis’.