Purification and characterization of antibacterial compounds of Pseudoalteromonas flavipulchra JG1

Pseudoalteromonas flavipulchra JG1 produces a protein PfaP and a range of small-molecule compounds with inhibitory activities against Vibrio anguillarum. The PfaP protein was purified from the extracellular products of JG1 by electroelution, and antibacterial activity was observed by an in-gel antibacterial assay. The complete amino acid sequence (694 aa) of PfaP was determined by de novo peptide sequencing and subsequent alignment with the proteome sequence of strain JG1. The calculated molecular mass of PfaP was 77.0 kDa. PfaP was 58 % identical to l-lysine oxidase AlpP of Pseudoalteromonas tunicata D2, and 54 % identical to the marinocine antimicrobial protein of Marinomonas mediterranea MMB-1. Five small molecules (compounds 1-5) with antibacterial activity, which were identified as p-hydroxybenzoic acid (1), trans-cinnamic acid (2), 6-bromoindolyl-3-acetic acid (3), N-hydroxybenzoisoxazolone (4) and 2'-deoxyadenosine (5), were purified by sequential column chromatography over silica gel, Sephadex LH-20 and RP-18 from ethyl acetate extract of strain JG1, and their structures were determined by NMR and MS. Brown compound 3, the only brominated compound, showed antibacterial activity against both Gram-positive and Gram-negative bacteria.