Halocins and sulfolobicins: The emerging story of archaeal protein and peptide antibiotics

Abstract

Production of antibiotic peptides and proteins is a near-universal feature of living organisms regardless of phylogenetic classification. Bacteriocins (proteinaceous antimicrobials from the domain Bacteria) have been studied for over 75 years, and the eucaryocins (proteinaceous antimicrobials from the domain Eucarya) since the early 1960s. However, one domain of organisms, the Archaea, containing hyperthermophiles, extreme halophiles and the methanogens, is just beginning to be scrutinized for the production of peptide antibiotics. Production of archaeal proteinaceous antimicrobials (archaeocins) from extreme halophiles (halocins) is a nearly universal feature of the rod-shaped haloarchaea. Halocin activity is first detectable in culture supernatants at the beginning of the transition into stationary phase, concomitant with an induction of transcription of the structural gene. Halocins are diverse in size, consisting of proteins as large as 35 kDa and peptide "microhalocins" as small as 3.6 kDa. The 36 amino acids of microhalocin HalS8 are located in the interior of a 311-residue pro-protein from which they are liberated by an unknown mechanism. Microhalocins are hydrophobic and robust, withstanding heat, desalting and exposure to organic solvents. Unlike the peptide bacteriocins and the eucaryocins, microhalocins possess a large number of neutral residues and are not cationic, leaving their mechanism(s) of action mostly a mystery. While microhalocins affect a variety of haloarchaeal genera (kingdom Euryarchaeota), they also exhibit cross-kingdom toxicity, inhibiting or killing Sulfolobus species (kingdom Crenarchaeota). Finally, archaeocins also are produced by the hyperthermophile "Sulfolobus islandicus". These 20-kDa protein antibiotics are not excreted into the environment, but are associated with small particles apparently derived from the cell's S-layer.

The Sulfolobicin Genes of Sulfolobus acidocaldariusEncode Novel Antimicrobial Proteins

“…Culture-independent surveys have shown them to be present in virtually every natural habitat (5). Archaea produce so-called archaeocins, but until now only a few of these antimicrobial (poly)peptides have been described (14,16,17). Halocins are archaeocins that are produced by halophilic euryarchaea (13).…”

Halocin Production From Haloarcula Hispanica, a Saltern Extremophile

“…Reported that halocin activity reached a maximum during the transition to stationary phase at the end of the exponential growth phase and then decreased to low levels, and reasoned this might be due to the rapid increase in gene expression level in the late stationary phase. Among the halocins investigated so far most of them are first detectable when culture of the producing cells enters the stationary growth phase (Shand et al, 1999 andShand, 2002 He et al (2006) reported that the maximum antagonistic activity was found in the precipitate obtained with 60% saturation of ammonium sulfate for the cell-free supernatant of Bacillus licheniformis. In the present attempt it was 70%.…”

“…O"Connor and Shand (2002) reported the microhalicins with molecular weight of 3.6kDa and 3.8kDa from the Halobacterium sp. whereas Sun et al (2005) reported slightly larger purified compound of 7.44 kDa.…”

Bacteriocins of Aquatic Microorganisms and Their Potential Applications in the Seafood Industry

“…Additionally, a relatively small number of bacteriocins from Archaeal species have also been characterized. A comprehensive review of bacteriocins from Bacteria and Archaea can be found elsewhere (O'Connor & Shand, 2002;Reeves, 1965;Riley & Gordon, 1999;Riley & Wertz, 2002a, 2002bTagg et al, 1976). Below are short descriptions of the bacteriocin classes of Bacteria and Archaea and examples of bacteriocins belonging to each class ( …”