碩士 國立中央大學 生命科學研究所 88 Abstract A soil bacterium, Pseudomonas putida SH1, was isolated from a petroleum-contaminated area in Taiwan. In our previously study, the bacterium catabolizes naphthalene, phenol, o-, m-, and p-cresol as sole source of carbon and energy to grow. Extradiol dioxygenases, catechol 2,3-dioxygenases (C23Os), involved in the cleavage of aromatic ring were induced when the bacterium was grew in minimal salts basal medium containing individual aromatic compound. Four of them were purified and characterized namely C23Os as C23Onap(SH1), C23OpheI(SH1), C23OpheII(SH1) and C23Oo-cre(SH1). The specific activities of C23Os induced by 3 isomers of cresol in crude cell extracts from P. putida SH1 was determined towards to catechol and and catabolic derivatives, 3-methylcatechol, 4- methylcatechol and 4-chrolocatechol. It showed the same substrate specificity, suggesting this strain converts o-, m-, and p-cresol to catechol probably by the same C23O. The thermal effect on C23O was then observed by the s