Isolation, identification and culture optimization of an alginate lyase-producing strain Microbulbifer sp. SH-1

Abstract:

[Objective] The aim of this study was to screen a strain with high alginate lyase activity and optimize the culture conditions of the strain. [Methods] Using sodium alginate as the sole carbon source, we screened and isolated microorganisms from the coastal soil of Zhangzhou, Fujian province, and a high-yield strain of alginate lyase was obtained. According to the morphological, physiological and biochemical characteristics and 16S rDNA sequence analysis, the target strain was identified. Then the enzyme production conditions were optimized by single factor and orthogonal test. [Results] Four strains with transparent circle to colony diameter ratio (D/d)>3 were obtained by cetylpyridine staining. DNS method was used to determine the activity of alginate lyase in the fermentation broth of four strains. The enzyme activity of strain SH-1 was the highest, reaching 315.5 U/mL. Based on morphological, physiological, biochemical and 16S rDNA sequencing identification, it was named Microbulbifer sp. SH-1. Through single factor and orthogonal test optimization, the optimum enzyme production medium was determined as follows (g/L):sodium alginate 10, NaCl 5, (NH₄)₂SO₄ 5, MgSO₄ 0.2, K₂HPO₄ 1 and FeSO₄ 0.02. Further optimization of culture conditions showed that SH-1 strain could be inoculated into 50 mL medium at initial pH 7.5 and 32℃ with 1% inoculation. The maximum enzyme activity of SH-1 strain could reach 757.9 U/mL under 240 r/min for 24-h shaking, 2.4 times higher than that before optimization. [Conclusion] The optimized conditions for SH-1 production provides reference for large-scale preparation of alginate lyase and further research.