Chemistry Reference
In-Depth Information
conditions for enzyme activity were 658C and pH 4.5-5.5 (Onishi and
Tanaka, 1997).
A patent for the production of galacto-oligosaccharides was taken out
by Onishi and Yokozeki (1992); it included Sirobasidium with a number of
other species.
5.4.1.4.2
The Extremophiles
Microorganisms isolated from environmentally extreme conditions are
of potential use for the industrial production of galacto-oligosaccharides. A
number of these have been studied with this objective. It would be a major
advantage if enzymatic conversions to oligosaccharides by the equilibrium
route could be performed at a very high temperature under acidic conditions.
A number of thermophiles have been examined for suitable
-galactosidases,
including strains of Thermus, Thermoaerobacter, Sulfolobus and Thermotoga
spp. Examples are given below.
Sulfolobus solfataricus
Sulfolobales are hyperthermophilic archaea from terrestrial volcanic sites
that grow in sulfur-rich hot acid springs, with optimum growth at 75-808C
and pH 2-3. S. solfataricus grows optimally at temperatures ranging from
70 to 908C and at pH 2-4. It can grow either lithoautotrophically by
oxidizing sulphur or chemoheterotrophically on reduced carbon com-
pounds. Pisani et al. (1990) studied the properties of a
-galactosidase in
the species and found it to be thermostable. Grogan (1991) examined in
more detail the properties of the
-glycosidase present and found that the
same enzyme exhibited both
-galactosidase and
-glucosidase activity. He
also noted the optimal reaction temperature to be 77-878Candtheoptimal
pH for
-galactosidase activity to be pH 4.9. Other thermophilic microor-
ganisms such as Thermotoga maritima can also produce galacto-oligosac-
charides by a thermostable recombinant
-galactosidase (She et al., 2001).
Thermotoga maritima
Thermotoga maritima, a rod-shaped bacterium belonging to the order Ther-
motogales, was originally isolated from a geothermal marine sediment. The
organism has an optimum growth temperature of 808C. The species metabo-
lizes many simple and complex carbohydrates.
Ji et al. (2005) prepared a recombinant
-galactosidase from a strain of
T. maritima in E. coli. They determined the stability and productivity of this
enzyme at a range of pH and up to 958C. Optimal conditions were pH 6 at
