Isolation and identification of moderately halophilic protease-producing bacteria from saline soils

Moderate halophiles are excellent sources of enzymes that are not only salt- stable, but also have optimal activities at a wide range of pH and temperature. The aim of this study was the isolation of moderately halophilic protease-producing bacteria from saline soils in Alborz province.
Material & Screening of the protease- producing halophilic bacteria was carried out by skim milk agar containing 5% NaCl. Enzyme assay was investigated by the colorimetric method and the effect of various parameters such as temperature, pH, and different NaCl concentrations on enzyme activity were assessed. Identification of the isolates was carried out by biochemical as well as molecular methods.
A total of 11 halophilic strains with proteolytic activity were isolated among which the strain B8 with higher clearance zone on skim milk agar and 3.2 Unit/mL supernatant activity was chosen for further analysis. The enzyme exhibited its optimal activity at the temperature of 40◦C, pH of 7.5 and NaCl concentration of 0-0.5 M, although at higher salinities (up to 3 M) activity was still remained. The enzyme was active at a broad pH range, keeping 60% of its activity at pH of 9.5. Phylogenetic analysis based on 16S rRNA gene sequencing identified the isolate as Halomonas. It was deposited in GenBank, with the name of Halomonas sp. strain HM_NG2.
These findings suggest that the protease secreted by the isolate of this study could be a good candidate for biotechnological applications due to its moderate thermo-stability and halloalculophytic properties.