**5. Acknowledgements**

We are very grateful to Bénédicte Michel for bacterial strains and continuous support and advice. We especially thank Estrella Guarino, Israel Salguero, Carmen Mata, Encarna Ferrera and Hasna Boubakri for their works and technical help. This work was supported by grants BFU2007-63942 to EG and BFU2007-64153, and P09-CVI-5428 to EV from the Ministerio de Ciencia e Innovación and Junta de Andalucía. EV is grateful to Dr. JB Schvartzman for training in 2D electrophoresis and helpful discussions along the years. EV is grateful to Dr. JB Schvartzman for training in 2D electrophoresis and helpful discussions.
