Secreted euryarchaeal microhalocins kill hyperthermophilic crenarchaea

Few antibiotics targeting members of the archaeal domain are currently avai lable for genetic studies. Since bacterial antibiotics are frequently direc ted against competing and related organisms, archaea by analogy might produ ce effective antiarchaeal antibiotics. Peptide antibiotic (halocin) prepara tions from euryarchaeal halophilic strains S8a, GN101, and TuA4 were found to be toxic for members of the hyperthermophilic crenarchaeal genus Sulfolo bus. No toxicity was evident against representative bacteria or eukarya. Ha locin S8 (strain S8a) and halocin R1 (strain GN101) preparations were cytos tatic, while halocin A4 (strain TuA4) preparations were cytocidal. Subseque nt studies focused on the use of halocin A4 preparations and Sulfolobus sol fataricus. Strain TuA4 cell lysates were not toxic for S. solfataricus, and protease (but not nuclease) treatment of the halocin A4 preparation inacti vated toxicity, indicating that the A4 toxic factor must be a secreted prot ein. Potassium chloride supplementation of the Sulfolobus assay medium pote ntiated toxicity, implicating use of a salt-dependent mechanism. The utilit y of halocin A4 preparations for genetic manipulation of S. solfataricus wa s assessed through the isolation of UV-induced resistant mutants. The mutan ts exhibited stable phenotypes and were placed into distinct classes based on their levels of resistance.