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

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

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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 Casters 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 Wooden Sleigh 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.