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New Linear Lipopeptides Produced by Pseudomonas cichorii SF1-54 Are Involved in Virulence, Swarming Motility, and Biofilm Formation

May 2013 , Volume 26 , Number  5
Pages  585 - 598

Ellen Pauwelyn,1,2 Chien-Jui Huang,1 Marc Ongena,3 Valérie Leclère,4 Philippe Jacques,4 Peter Bleyaert,2 Herbert Budzikiewicz,5 Mathias Schäfer,5 and Monica Höfte1

1Department of Crop Protection, Laboratory of Phytopathology, Ghent University, Coupure Links 653, 9000 Ghent, Belgium; 2Inagro vzw, Ieperseweg 87, 8800 Rumbeke, Belgium; 3Walloon Centre for Industrial Biology, University of Liège–Gembloux Agro-Bio Tech, Passage des Déportés 2, 5030 Gembloux, Belgium; 4Laboratoire de Procédés Biologiques, Génie Enzymatique et Microbien (ProBioGEM), Université de Lille Sciences et Technologies, F-59655 Villeneuve d'Ascq Cedex, France; 5Institut für Organische Chemie, Universität zu Köln, Greinstr. 4, 50939 Köln, Germany

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Accepted 5 February 2013.

Pseudomonas cichorii is the causal agent of lettuce midrib rot, characterized by a dark-brown to green-black discoloration of the midrib. Formation of necrotic lesions by several plant-pathogenic pseudomonads is associated with production of phytotoxic lipopeptides, which contribute to virulence. Therefore, the ability of P. cichorii SF1-54 to produce lipopeptides was investigated. A cell-free culture filtrate of SF1-54 showed surfactant, antimicrobial, and phytotoxic activities which are typical for lipopeptides. High-performance liquid chromatography analysis of P. cichorii SF1-54 culture filtrate revealed the presence of seven compounds with lipopeptide characteristics. Two related lipopeptides, named cichofactin A and B, were studied in more detail: they are linear lipopeptides with a decanoic and dodecanoic lipid chain, respectively, connected to the N-terminus of an eight-amino-acid peptide moiety. Both cichofactins are new members of the syringafactin lipopeptide family. Furthermore, two nonribosomal peptide synthethase-encoding genes, cifA and cifB, were identified as responsible for cichofactin biosynthesis. A cifAB deletion mutant no longer produced cichofactins and was impaired in swarming motility but showed enhanced biofilm formation. Upon spray inoculation on lettuce, the cichofactin-deficient mutant caused significantly less rotten midribs than the wild type, indicating that cichofactins are involved in pathogenicity of P. cichorii SF1-54. Further analysis revealed that P. cichorii isolates vary greatly in swarming motility and cichofactin production.

© 2013 The American Phytopathological Society