The effect of soluble alginate and calcium on beta-galactosidase activity produced by the thermotolerant, ethanol-producing yeast strain Kluyveromyces marxianus imb3

Since it has previously been demonstrated that ethanol production by the thermotolerant yeast strain, Kluyveromyces marxianus IMB3 is more efficient in calcium alginate-based immobilization systems during growth on lactose-containing media, it was decided to examine the separate effects of soluble alginate and free calcium on the beta-galactosidase activity produced by that organism. It was found that the presence of Ca2+ significantly increased the thermal stability of the activity at 45 degrees C, although the pH and temperature optima remained the same in the presence and absence of that cation. It was also found that the presence of 2% (w/v) sodium alginate (soluble) had a very limited positive effect on the thermal stability of the enzyme at 45 degrees C, although it was found that activity was very significantly stimulated at that temperature. The activity was found to have an enhanced thermal stability at 30 OC in the presence of sodium alginate. The presence of sodium alginate in assay mixtures had no significant effect on the Km of the activity for the substrate o-nitrophenyl-beta-D-galactoside. The results observed in the presence of either free calcium or soluble alginate may at least partially explain enhanced ethanol production by this microorganism in alginate-based immobilization systems.