Purification and partial characterization of marinocine, a new broad-spectrum antibacterial protein produced by Marinomonas mediterranea

This work describes the purification and partial characterization of a novel antibacterial compound, here named marinocine, produced by Marinomonas mediterranea, a melanogenic marine bacterium with rich secondary metabolism. The antibacterial compound is a protein detected in the medium at death phase of growth. It has been purified to apparent homogeneity from the supernatants of cultures by means of ethanol precipitation followed by column chromatographies on DEAE-Sephadex and Sephacryl HR-200. The protein has an apparent molecular mass of 140-170 kDa according to gel permeation chromatography and non-denaturing SDS-PAGE, although in denaturing SDS-PAGE two mayor bands of 97 and 185 kDa appear. Marinocine is relatively heat-stable and shows a great resistance against many hydrolytic enzymes such as glycosidases, lipase, and proteases. The antibacterial range of the molecule includes Gram-positive and Gram-negative microorganisms, as well as some nosocomial isolates, Staphylococcus aureus and Pseudomonas sp., highly resistant to classical antibiotics. By contrast, marinocine did not show any effect on the eukaryotic microorganisms tested. Regarding eukaryotic CHO cells, the decrease on viability was much lower than the one observed on bacterial cells.