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pp.308-314
Two hundred and twenty three yeast strains were randomly isolated from Korean traditional nuruk. Among them, six urease producing yeast strains (designated JJA, JJB, JJ22, SHA, SHC and SH10) were selected on the Christensen urea agar plates. They showed the same pattern in the PCR-RFLP analysis of the ITS I-5.8S-ITS II region digested with HaeIII and HinF1 restriction endonucleases. Its DNA sequences showed 100% (strains SHA, SHC and SH10) and 99.8% (strains JJA, JJB and JJ22) identity with those of Issatchenkia orientalis type strain ATCC 24210. Phylogenetic analysis resulted in that all the strains were closely related to I. orientalis. Two representative strains, JJ22 and SH10, showing the highest urease activities were selected for further characterization. Their morphological, physiological and biochemical characteristics were also the same as I. orientalis. Therefore, both the two strains were identified as I. orientalis. They could grow at a wide range of temperature between 20-40℃ as well as pH between 2.0 and 10.0. However, a higher level urease activity were obtained at acidic pH than that at alkalic pH. The maximal level of urease activity was obtained at 30℃ (strain SH10) or 35℃ (strain JJ22) and in a liquid medium adjusted to the initial pH 5.0.
