Purification and characterization of a novel extracellular inulinase from a new yeast species Candida kutaonensis sp. nov. KRF1T

A novel extracellular exoinulinase was purified and characterized from a new yeast strain KRF1T, and the gene encoding the enzyme was successfully cloned. The enzyme was stable at low pH between 3.0 and 6.5. The Km and Vmax values of the purified enzyme for inulin were 2.3 mg/mL and 4.8 mg/min, respectively. The optimum temperature of the inulinase was 50 °C, and the enzyme remained 78 % of activity at 60 °C for 2 h. The inulinase showed an amino acid sequence identity of 58 % to its closest homolog in Meyerozyma (Pichia) guilliermondii. In the secondary structure, the domain G (VMEVH) of the enzyme contained three unique residues (V, M, and H). Compared with previously reported inulinases, the enzyme from strain KRF1T displayed strong acid resistance, notable thermostability, and high affinity for the substrate of inulin. Based on sequence analysis of the 26S rDNA D1/D2 domain and phenotypic characterization, the yeast strain KRF1T was found to represent a novel anamorphic, ascomycetous yeast species. A complete description of the species is given and the name Candida kutaonensis sp. nov (type strain = KRF1T = AS 2.4027T = CBS 11388T) is proposed.