A Marine Isolate of Secretes a Pumilacidin Active against .

Producing antimicrobials is a common adaptive behavior shared by many microorganisms, including marine bacteria. We report that SF214, a marine-isolated strain of , produces at least two different molecules with antibacterial activity: a molecule smaller than 3 kDa active against and a molecule larger than 10 kDa active against We focused our attention on the anti- molecule and found that it was active at a wide range of pH conditions and that its secretion was dependent on the growth phase, medium, and temperature. A mass spectrometry analysis of the size-fractionated supernatant of SF214 identified the small anti- molecule as a pumilacidin, a nonribosomally synthesized biosurfactant composed of a mixture of cyclic heptapeptides linked to fatty acids of variable length. The analysis of the SF214 genome revealed the presence of a gene cluster similar to the locus encoding the multimodular, nonribosomal peptide synthases found in other surfactant-producing bacilli. However, the cluster of SF214 differed from that present in other surfactant-producing strains of by the presence of an insertion element previously found only in strains of .