Characterization of a new thermostable esterase from the moderate thermophilic bacterium Bacillus circulans

The new moderate thermophilic bacterial strain MAS2, previously isolated at 50 degrees C on a mineral medium containing triolein as sole carbon and en ergy source has been characterized and identified as Bacillus circulans. Th is strain does not produced lipase but an esterase activity which productio n was not enhanced by addition of Tween 80 or triolein in the culture mediu m. The reaction rate was maximum at 60 degrees C. After 1 h incubation at 7 0 degrees and 85 degrees C the remaining activities were 100% and 50%, resp ectively, showing the high thermostability of this esterase activity. Optim um pH was in the range 8.5-9.5 with an important (60%) activity retained at pH 10.0. The kinetic constants for p-nitrophenyl caprylate (pNPC8) hydroly sis were K-M = 0.24 mM and V-m = 4.3 nmol/min mg. Using fatty acids with di fferent chain lengths, the highest activity was observed on pNPC2. which co nfirmed the esterase nature of the enzyme. A significant activity remained on mid-chain-length fatty acids such as pNPC6 and pNPC8. Because of its hig h thermostability, activity at alkaline pH and broad specificity range for fatty acids, this enzyme showed high potential for use in biocatalysis. (C) 2000 Elsevier Science B.V. All rights reserved.