| An agarase-producing bacterium was selected from rotting seaweed. The activity of agarase in fermented broth was 33.6 U/mL when the strain DT-3 had been incubated for 36 hours. It was identified as Halomonas sp. and had 99% homology to Halomonas alkantarctica by means of 16S rDNA analysis and compared analysis results with NCBI database. We named the strain as Halomonas sp. DT-3.The strain Halomonas sp. DT-3 was treated with UV and DES respectively. After treatment, an effectively agarolytic bacterium DT-3-57 was selected and the activity of agarase in fermented broth was raised to 62.7 U/mL which was one time more than the ability of original strain. Generally the effect of mutagen DES was better than UV on improving the agarase activity. With the single factor test and orthogonal design test, the optimal culture medium for the strain DT-3-57 to produce agarase was studied as: agar 0.5%, peptone 0.3%, yeast powder 0.3%, CaCl2 1.0 mmol/L,NaCl 3.5%, K2HPO4 0.2 mmol/L,MgSO4 0.1 mmol/L and the optimal culture conditions were studied as: medium pH 7.5, incubating temperature 28℃, rotation rate 120 rpm and amount of inoculation 1%. The activity of agarase in fermented broth was 76.3 U/mL when Halomonas sp. DT-3-57 had been incubated for 36 hours under above optimal fermentation conditions.The basic properties of agarase produced by Halomonas sp.DT-3-57 were studied. The agarase was purified 10.57-fold through ammonium sulfate precipitation,concentration and Sephadex G-100 gel filtration. The purified agarase appeared to be homogeneous and had a molecular mass of approximately 90 KDa as estimated by SDS-PAGE. The basic properties of agarase were studied as follows: the optimal reaction temperature, pH and agar concentration of the agarase were 40℃, 7.0 and 0.7-0.8% respectively. The agarase activity was increased by adding Mg2+,K+,Ca2+,Ba2+ with modest ion concentrations. The effect of Ca2+ was remarkable in the assay system.
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