To identify the small molecules responsible for the observed biofilm inhibition and disruption, we chose a medium polarity fraction (E fraction that eluted at 60% MeOH/Water) produced by Pseudoalteromonas piscicida (EM11-4). This particular fraction inhibited 96% of biofilm formation in S. aureus without impacting viability. High performance liquid chromatography (HPLC) under reverse phase conditions led to isolating pseudochelin A (6) (Fig. ). Pseudochelin A is a siderophore previously purified from P. piscicida S2040 isolated from sediment off the northwestern coast of Australia. We confirmed the structure of 6 by comparing HR-ESI-MS, 1D and 2D NMR spectra, and a circular dichroism spectrum to published data (Fig. ).