Isolation and some properties of β-galactosidase from the thermophilic bacterium Thermus thermophilus

The highest beta-galactosidase activity in Thermus thermophilus cells was achieved after 40h of cultivation at 70 degrees C in a medium containing 0.8% peptone, 0.4% yeast extract and 0.2% NaCl. After the addition to the medium of 2% of lactose or galactose, enzyme synthesis in the cells increased by about 33% and 61% of its constitutive value. The thermostable beta-galactosidase isolation and partial purification involved extraction in 0.01M phosphate buffer at pH 7.2, ammonium sulphate precipitation, dialysis and gel filtration on Sephadex G-200 or lyophilization. The highest recovery yield of activity during the isolation process was about 72% of its total value in the extract. The gel filtration step resulted in an increase of beta-galactosidase specific activity of two-fold more than the ammonium sulphate precipitate. The crude enzyme obtained exhibited highest activity at pH 6.6 and 87 degrees C. Decimal reduction times of activity at 75, 80, 85, 90 and 95 degrees C were 174, 50, 22, 5.5 and 0.9h, respectively. (C) 1998 Elsevier Science Ltd. All rights reserved.