Production of novel alkalitolerant and thermostable inulinase from marine actinomycete Nocardiopsis sp. DN-K15 and inulin hydrolysis by the enzyme

An actinomycete strain Nocardiopsis sp. DN-K15 showing high inulinolytic activity was isolated from marine sediment of Jiaozhou Bay in China. Under optimal conditions, Nocardiopsis sp. DN-K15 produced 25.1 U/ml of inulinase within 60 h of fermentation at shake flask level, which was 2.7-fold higher than the level in the basal medium. The optimal pH and temperature of the inulinase from strain DN-K15 were determined to be 60 °C and pH 8.0, respectively. The inulinase was highly active over a wide pH range (5.0–11.0) and retained more than 81 % of residual activity after incubation at 60 °C for 1 h, indicating its alkali-tolerant and thermostable nature. Thin layer chromatography analysis revealed that fructose was the main product of inulin hydrolysis, indicating its exoinulinase activity. The high yield of extracellular inulinase combined with its novel enzymatic property made Nocardiopsis sp. DN-K15 a potential candidate in biotechnological and industrial applications.