Screening of thermotolerant bacteria producing lipase from natural sources

Screening of thermotolerant bacteria producing lipase from natural sources

Aran H-Kittikun, Asst. Prof., D. of Industrial Biotech., F. of Agro-Industry, PSU.
Thiraratana Prachumratana, D. of Industrial Biotech., F. of Agro-Industry, PSU.
Poonsuk Prasertsan, Assoc. Prof., D. of Industrial Biotech., F. of Agro-Industry, PSU.
Kimiyasu Isobe, Assoc. Prof,. 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 : lipase, thermotolerant bacteria

One hundred samples from oil contaminated soils were collected from palm oil mills, sewage water, market places and restaurants in southern Thailand. The samples were directly added to enrich-ment medium (NH₄NO₃ 0.5, K₂HPO₄ 0.2, KH₂PO₄ 0.1, MgSO₄. 7H₂O 0.02, peptone 0.2, gum arabic 2.0 g/L) containing palm oil as a carbon source and transferred 3 consecutive times in the same me- dium on a shaker at 30^oC. The enriched samples were screen on palm oil agar. One hundred and twenty-three isolates producing clear zones around the colonies were collected. They were 58 Gram positive bacteria and 65 Gram negative bacteria. Five isolates were chosen for further study. Lipase activity in the culture broth was assayed using palm olein as substrate and the acid liberated was ti- trated with sodium hydroxide. The isolate PAB 3 and PAB 5 had yellow pigment and produced 3.92 and 4.03 U of lipase activity in the palm oil medium after shaking for 5 days at 45^oC. The isolate PAB 7 was pink-purple in color and produced 4.80 U of lipase activity. The isolate PAB 10 had orange pigment and produced 3.56 U of lipase activity, while the isolate PAB 11 had no pigment and pro- duced 4.12 U of lipase activity. The isolate PAB 11 was able to use linseed oil as a carbon source and produced 7.20 U of lipase activity after shaking at 30^oC for 24 h. The crude enzyme had optimal activity at pH 6-7. However, the enzyme was not stable at high temperature as only 32% of its acti- vity was retained after incubation at 45^oC for 30 min.

Growth and lipase production by these three isolates will be compared. The strain producing high lipase activity at temperature higher than 45oC will be chosen for optimization of lipase produc-tion and purification.

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