Screening of thermostable lipolytic enzyme from acid- and thermotolerant fungi
Kimiyasu Isobe, Assoc. Prof,. Laboratory of Agricultural Microbiology, F. of Agriculture, Iwate U., Japan
Nobuaki Inoue, Laboratory of Agricultural Microbiology, F. of Agriculture, Iwate U., Japan
Kiyohiro Kamata, Laboratory of Agricultural Microbiology, F. of Agriculture, Iwate U., Japan
Aran H-Kittikun, Asst. Prof., D. of Industrial Biotech., F. of Agro-Industry, PSU.
Norio Wakao, Laboratory of Agricultural Microbiology, F. of Agriculture, Iwate U., Japan
Corresponding e-mail : haran@ratree.psu.ac.th
Presented : The 2nd JSPS-NRCT Joint Seminar on Development of Thermotolerant Micro-
bial Resources and their Applications, 21-25 November 2000 Yamaguchi, Japan
Key words : lipolytic enzyme, thermotolerant fungi
For the screening of a new thermostable lipolytic enzyme, we used the extreme conditions combined with a strong acid pH and rather high temperature. On agar plate of pH 1.0 or 2.5, 117 strains of fungi were isolated from 191 kinds of soil and water samples by culturing at 42oC for 7 days (11 strains from pH 1.0 and 106 strains from pH 2.5). All isolated fungi grew well at 30 and 42oC, and 7 strains also grew at 50oC (pH 3.0). In addition, all isolates grew well over pH 2.0, when the isolated
fungi were cultured in a liquid medium of initial pH 1.0 to 7.0 at 42oC. Therefore, the isolated fungi
were classified into acid- and thermotolerant fungi, but not into acidophilic fungi or thermophilic
fungi. When these isolated fungi were cultured in a liquid medium, pH 3.0, at 30 and 42oC for 7 days, the final pH of the culture broth varied between 2.5 and 9.0 at both temperatures, and 66 strains pro-duced a lipolytic enzyme in the culture broth at 42oC. Among these strains, 23 strains showing high lipolytic activity were selected by the difference of final pH of the culture broth, and cultured at pH
3.0 and 42oC. The thermostable lipolytic enzymes, which remained more than 90% of the enzyme activity after heating at pH 7.0 and 50oC for 60 min, were obtained from the strains showing neutral
or alkaline pH of culture broth. The acid- and thermostable lipolytic enzymes, which remained more than 60% of the enzyme activity at pH 2.0, were also obtained from the strains keeping acid pH.
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