Downloaded from www.microbiologyresearch.org by IP: 23.22.6.154 On: Thu, 04 Feb 2016 05:38:18 Transcriptome analysis of Yersinia pestis in human plasma: an approach for discovering bacterial genes involved in septicaemic plague Sylvie Chauvaux, 1 Marie-Laure Rosso, 2 Lionel Frangeul, 3 Ce ´ line Lacroix, 4 Laurent Labarre, 5 Ange ` le Schiavo, 4 Michae ¨ l Marceau, 2 Marie-Agne ` s Dillies, 4 Jeannine Foulon, 1 Jean-Yves Coppe ´ e, 4 Claudine Me ´ digue, 5 Michel Simonet 2 and Elisabeth Carniel 1 Correspondence Sylvie Chauvaux chauvaux@pasteur.fr 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 Ge ´ noscope, Evry, France Received 22 January 2007 Revised 14 May 2007 Accepted 14 May 2007 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 6C 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 6C, 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 6C and may thus represent new virulence factors that are important during the septicaemic phase of human plague. INTRODUCTION Yersinia pestis is a highly infectious, Gram-negative bacterium that causes plague. The pathogen belongs to the family Enterobacteriaceae and is subdivided into three classic biovars [Antiqua, Medievalis and Orientalis (Devignat, 1951)] and one additional biovar [designated Microtus or Pestoides (Zhou et al., 2004)] which is thought to represent the ancestral Y. pestis branch (Achtman et al., 2004). Although plague is primarily a zoonotic disease, humans are also extremely susceptible to infection, with recent reports of about 2000 cases per year (http://www. who.int/mediacentre/factsheets/fs267/en/). Three main clin- ical forms are designated according to the route of infection (Dennis et al., 1999). Bubonic plague is the most common form and results from the bite of an infected flea. Pneumonic plague is less common but is considered to be highly contagious, since it is transmitted from human to human by aerosols; the incubation period is very short (1–3 days) and death ensues almost invariably if appropriate antibiotic therapy is not initiated within 18–24 h of disease onset. Septicaemic plague is the least frequent and most fulminat- ing, fatal form of plague. It results from direct penetration of Abbreviation: QRT-PCR, quantitative real-time PCR. A supplementary figure showing QRT-PCR confirmation of transcrip- tome 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’. Microbiology (2007), 153, 3112–3123 DOI 10.1099/mic.0.2007/006213-0 3112 2007/006213 G 2007 SGM Printed in Great Britain