In this study, a yellow pigmented bacterial strain, designated C2, was recently isolated from the encrusting pore coral Montipora aequituberculata, which was collected from the Kenting coast of Southern Taiwan. Phylogenetic analyses based on 16S rRNA gene sequences indicate that strain C2 belongs to the genus Pseudoalteromonas and that its only closest neighbor is Pseudoalteromonas flavipulchra NCIMB 2033(T) strain. Based on the antibiogram assay, strain C2 shows potent antibacterial activity against several methicillin-resistant Staphylococcus aureus (MRSA) strains. Strain C2 can synthesize an antibacterial protein with a molecular mass of 60 kDa, and its isoelectric point is approximately 9.4. Liquid chromatography-tandem mass spectrometry analyses reveal close similarity of this antibacterial protein with the antibacterial protein AlpP from the marine bacterium Pseudoalteromonas tunicata D2. This study explores the nature of this antibacterial protein such as L-amino acid oxidase with broad substrate specificity. The enzyme is most active with L-Lys, L-Met, L-Glu, L-Leu, L-Gln, L-Tyr and L-Phe, and the hydrogen peroxide generated by its catalysis mediates antibacterial activity. This is the first report on a marine bacterium P. flavipulchra producing antibacterial activity by generating hydrogen peroxide through its enzymatic activity of L-amino acid oxidase against MRSA. (C) 2010 Elsevier Inc. All rights reserved.