Methods: Purification and characterization of peptides was attained using high performance liquid chromatography and a pentaquadrupole mass-spectrometer. Analysis of siderophores from Xac involved solid-phase extraction and interaction with iron III prior to MS. In AFM a microscope tip scans the surface. An up and down movement of the tip generates topographical images, which were used to study the interaction of peptides with substrates and with bacterial membranes.

Results: Bacterial toxins, siderophores and other peptides produced nonribosomally, are synthesized by nonribosomal peptide synthetases (NRPSs). We have studied NRPSs predicted in the genomes of Xac and Xcc and are currently looking at the production of a siderophore. In addition, we have isolated lipopeptides from a novel strain of Bacillus subtilis and are investigating the effect of these antibiotics on both Xac and Xcc by AFM. The method was successfully employed to study the auto-organization of lipopeptides on the surface of muscovite mica and silicon. In addition it was successfully employed to characterize the activity of lipopeptides on bacterial cell membranes (Xac and Xcc).

Conclusions: Xac produces siderophores, which bind to iron and other metals  potentially forming a 3:1 complex. Lipopeptides of B. subtilis form bilayers on both mica and silicon. They interact with bacterial cell membranes. For a fixed concentration they were shown to disrupt cells of Xcc, but not Xac. Interestingly, the latter was also shown to harbor genes potentially involved in lipopeptide assembly.