**Abstract**

Members of extremely halophilic archaea, currently consisting of more than 56 genera and 216 species, are known to produce their specific bacteriocin-like peptides and proteins called halocins, synthesized by the ribosomal pathway. Halocins are diverse in size, consisting of proteins as large as 35 kDa and peptide "microhalocins" as small as 3.6 kDa. Today, about fifteen halocins have been described and only three genes, halC8, halS8 and halH4, coding C8, S8 and H4 halocins respectively have been identified. In this study, a total of 1858 of complete and nearly complete genome sequences of Halobacteria class members were retrieved from the IMG and Genbank databases and then screened for halocin encoding gene content, based on the BLASTP algorithm. A total of 61 amino acid sequences belonging to three halocins classes (C8, HalH4 and S8) were identified within 15 genera with the abundance of C8 class. Phylogenetic analysis based on amino acids sequences showed a clear segregation of the three halocins classes. Halocin S8 was phylogenetically more close to HalH4. No clear segregation on species and genera levels was observed based on halocin C8 analysiscontrary to HalH4 based analysis. Collectively, these results give an overview on halocins diversity within halophilic archaea which can open new research topics that will shed light on halocins as marker for haloarchaeal phylogentic delineation.

**Keywords:** archaea, bioinformatics, diversity, halocins, phylogeny

## **1. Introduction**

Microorganisms of the third domain of life, Archaea, have been cultivated and described for more than 100 years [1], however, they have been first assigned to the Bacteria domain because of their great phenotypic similarities. In the late 1970s, Carl Woese and his collaborators, recognized the Archaea as the third domain of life on earth based on molecular phylogenetic analyses [2]. The dichotomous (eukaryotic/prokaryotic) classification was no longer valid, leading to a reclassification of

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The biotopes colonized by these microorganisms, are supposed to approach to the primitive terrestrial atmosphere (high salinity or pH, devoid of O2, rich in H2 and CO2 constituting the raw materials for the production of methane) [10]. They present spectacular adaptations, especially in extreme environments. We distinguish: (i) Thermophilic Archaea: living at high temperatures (60–80°C) (ii) Hyperthermophilic Archaea: living at very high temperatures (up to 121°C); (iii) Psychrophilic Archaea: prefering low temperatures (below 15°C) [11]; (iv) Halophilic Archaea: colonizing very saline environments (3–5 M NaCl) such as the Dead Sea [12, 13]; (v) Acidophilic Archaea: living at low pH (as low as pH 1 and dying at pH 7) and Alkaliphilic Archaea: thriving at high pH (up to 9) [14].
