Molecular identification of a novel inulinolytic fungus isolated from and grown on tubers of Helianthus tuberosus and statistical screening of medium components

Abstract

Of 24 fungi belonging to more than five genera isolated from tubers of rotten Helianthus tuberosus, 11-inulinolytic active isolates were able to develop halo zones around their fungal colonies, indicating inulinase activity. Alternaria, Aspergillus, Fusarium, Pencillium and Trichoderma were the most common inulinolytic genera, representing more than 90 % of the total positive inulinolytic fungi. Aspergillus tamarii and Pencillium citrinum quantitatively recorded better growth (5.5 and 4.7 mg ml⁻¹) and inulinase production (21.53 and 20.15 U ml⁻¹) in submerged culture. The enzyme preparation showed also invertase activity. Aspergillus tamarii, as the most potent producer of inulinase, was identified using the Inter Transcribed Spacer marker. The sequence comparisons showed that our molecularly identified strain (GU295949) is related more closely to A. tamarii strains of the gene bank. Statistical screening using the fractional factorial Plackett-Burman design with 12 run was applied for screening ten variables, the low levels of pH (4.8), inoculum size (10³ spore g⁻¹), NH₄NO₃ (1.0 mg g⁻¹) and MgSO₄ (0.12 mg g⁻¹), were the most significant variables on A. tamarii inulinase production. The high inulinase/invertase ratio (1.841–4.293) classified the enzyme preparation as inulinases, which can be used efficiently in production of fructose syrup from tubers of H. tuberosus.