PURIFICATION AND CHARACTERIZATION OF A NOVEL ANTIBACTERIAL PROTEIN FROM THE MARINE BACTERIUM D2

A biofilm-forming marine bacterium, D2, isolated from the surface of t he tunicate Ciona intestinalis, was found to produce a novel, 190-kDa protein with antibacterial activity, The protein contained at least tw o subunits of 60 and 80 kDa, joined together by noncovalent bonds, and was shown to be released by D2 cells into the surrounding medium duri ng stationary phase, N-terminal sequence analysis revealed no close si milarity of this protein to any other proteins within the Swiss Prot d atabase, Bacteriocidal activity against a wide variety of marine and m edical bacterial isolates was observed, 77% of the strains tested bein g sensitive to the protein, Bacterial strains varied in their resistan ce to the D2 protein, with D2 itself being among the most sensitive wi th an MBC in liquid suspension of 4 mu g/ml. An apparent increased res istance of D2 to the protein as the cells progressed further into stat ionary phase was observed and seen as a possible explanation for its s urvival despite the production of an autoinhibitory factor, The abilit y of the D2 bacterium to produce an antibacterial factor in addition t o its inhibitory effects on marine invertebrates and algae (S. Egan et al., unpublished data) indicates that D2 has the potential to greatly affect the survival of a range of colonizers of the marine surface en vironment.