Identification and characterization of a halocin-producing haloarchaeon isolated from Pachpadra salt lake.

Haloarchaea are known to produce antimicrobial proteins, halocins which are generally stable at extreme conditions suggesting their potential biotechnological applications. Here, we report a halocin-producing haloarchaeon isolated from salt lake and identified as Haloferax larsenii HA4 using partial 16S rDNA sequence and biochemical properties. Whole-cell methanolysate showed ether-linked lipids, which is a characteristic feature of haloarchaea. Strain HA4 was able to grow at pH 6·0-10·0 and 15-30% NaCl. The growth response was normal but antimicrobial activity was detected only during the log-phase. Crude halocin HA4 was active in the pH range of pH 2·0-10·0 with stability up to 100°C. Cell-free supernatant (CFS) was also stable in different organic solvents and detergents tested. However, halocin activity was reduced after treatment with proteinase K suggesting the proteinaceous nature of the active compound. Concentrated CFS showed the presence of several proteins from 6·5-66 kDa but bioassay suggested ~14 kDa protein as halocin. Crude halocin preparation showed cytocidal activity against indicator strain, H. larsenii HA10 and inhibited the growth of other related strains such as H. larsenii HA3, HA8, HA9 and HA10.