Purification and biological characterization of halocin C8, a novel peptide antibiotic from Halobacterium strain AS7092

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Abstract
Halocins are bacteriocin-like proteins or peptides produced by many species of the family Halobacteriaceae. Halocin C8, excreted by the Halobacterium strain AS7092, is a single 6.3-kDa polypeptide with an isoelectric point of 4.4, which is sensitive to proteinase K but not to trypsin. Halocin C8 is quite stable, as it can be desalted, boiled, frozen, subjected to organic solvents, and stored in culture supernatant at 4°C or in dH2O at −20°C for more than 1 year without losing activity. The purification of this halocin was achieved by combination of tangential flow filtration (TFF), Sephadex G50 and DEAE-sepharose chromatography. The N-terminal amino acid sequence was also determined by Edman degradation. Halocin C8 appeared to have a very wide activity spectrum, including most haloarchaea and even some haloalkaliphilic rods. When a sensitive strain of Halorubrum saccharovorum was exposed to halocin C8, the treated cells swelled at the initial stage, the cell wall appeared to be nicked and the cytoplasm was then extruded out, and the whole cell was eventually completely lysed. These results indicate that halocin C8 is a novel microhalocin and its primary target might be located in the cell wall of the sensitive cells.