Isolation, screening and identification of haloarchaea with chitinolytic activity from hypersaline lakes of Iran

Abstract

Halophiles produce stable enzymes under extreme conditions. The scant information about chitinolytic haloarchaea led us to conduct the present study in order to isolate and screen native halophilic archaea with chitinolytic activity and to optimize the enzyme production conditions. Among 500 haloarchaeal strains isolated from water samples from different hypersaline lakes of Iran, five strains showed chitinolytic activity. Based on biochemical, morphological and molecular analyses, we established that all five potent strains belonged to the genus Natrinema. Besides, observing chitinase function in culture media, through an additional molecular test the presence of the chitinase gene in chitinase-producing strains was also confirmed by PCR amplification. Compared with other potent strains, Natrinema sp. strain BS5 showed significant chitinase production. The production of chitinase in strain BS5 accompanied growth, started at the logarithmic phase and increased to its maximum level at the beginning of the stationary phase. Maximum chitinase production was obtained at 37°C, pH 7.5, 3 M NaCl and 1% colloidal chitin. The strain BS5 showed 38%, 30%, 24% and 28% decreases in enzyme production at 40°C, pH 8, 3.5 M NaCl and 0.5% substrate, respectively. This strain was able to produce the enzyme in NaCl 4 M and in the absence of MgCl 2 and MgSO 4 . This study revealed the strong potential of the genus Natrinema to produce chitinase at high salt concentrations without Mg 2+ requirement.