β-GALACTOSIDASE ACTIVITY OF MEIOTHERMUS RUBER CELLS

Freeze-dried cells of Meiothermus ruber catalyses cleavage of o-nitrophenyl-β-D-galactopiranoside (oNPβ-gal) and conversion of lactose into glucose and galactose. The permeabilization with 2% toluene, 20% ethanol and 20% acetone increased enzymatic activity from 74.87 U/g of lyophilized cells up to 129.44, 114.38 and 90.19 U/g, respectively. Ethanol was an effective permeabilizing agent and its efficiency was dependent on the concentration, the incubation time and incubation temperature. The Km values for the untreated and permeabilized cells were 2.94 mM and 2.26 mM but Vmax values were 122 µmol/min and 193 µmol/min, respectively. The optimum pH for the β-galactosidase activity in the untreated and permeabilized cells were 6.5 and optimum of temperatures 65C. The stability of enzymatic activity in M. ruber cells incubated for 1 h at pH 6.5 was almost unchanged at temperatures below 65C. PRACTICAL APPLICATIONS The current study shows that freeze-dried permeabilized cells of Meiothermus ruber can be used instead of isolated β-galactosidase. It leads to elimination of expensive purification procedures and assures longer half-life time of enzyme activity. Application of such biocatalyst for lactose hydrolysis in milk products for human consumption is limited until designation of the Generally Recognized As Safe status of Meiothermus ruber. It can be employed, however, for other purposes, e.g., for production of alkyl glycosides, a group of non-ionic surfactants with a variety of applications in detergents, cleaning agents, personal care products and pharmaceuticals.