Mathias Schäfer,5 and
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
Go to article:
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