PRODUCTION Of NUTRIENT SOURCES FOR RHIZOBIUM

These results indicated that the cooperation of starch-utilizing strain and glycerol-producing
isolate could not support the glycerol production. It might cause from the competition occuring when
both population. The competition also determines the different species of yeast that are often found in
mixed cultures such as in the lambic main fermentation (Granse, 1934).
Under competition conditions, organisms better adapted for new situations may be selected.
From the result of section 3.2, 5% of glucose in YEPD medium were used to screen sugar alcohol
production capability of yeasts. Yeast isolates LIY2, COY1, and FAY2 produced the high amount of
glycerol in both cultured media and cell lysates. In term of"polyols or sugar alcohols", accumulated
intracellular polyols have at least three major physiological functions: namely they act as: 1)
osmoregulators, 2) food reserves, and 3) protectors of enzyme activity at low levels of a w substances
(Brown, 1978). Yeasts accumulated glycerol as the primary osmoregulatory solute (Adler et al.,
1985). From results of this study the reducing sugar concentration in cultured medium was
approximate 0.4-0.5% (w/v). It might not be sufficient for cells to accumulate sugar alcohols, but
enough for growth. With regard to polyol catabolism, over 50% of yeasts surveyed could aerobically
use glycerol, D-glucitol (sorbitol) and D-mannitol while fewer than 10% of species utilized galactitol
(Walker, 1998). The glycerol produced and released into the cultured medium by glycerol-producing
yeast isolates LIY2, COY1, and FAY1 could be used as the carbon source for both yeast isolate Y69
and the glycerol-producing strains. Thornton and Eustace (1986) suggested that glycerol formation is
the result of competition between two enzymes, glycerol-3-phosphate dehydrogenase and alcohol
dehydrogenase. An increase in the specific activity of the enzyme, glycerol-3-phosphate
dehydrogenase, would increase the yield of glycerol. So the yeast strain might use the route of ethanol
production via changes of reducing sugars to pyruvate, then pyruvate to acetaldehyde, and finally to
ethanol.
3.6�Optimization of some glycerol and mannitol production conditions
To obtain the efficient production of glycerol and mannitol from starch, some intrinsic factor
of fermentation, and inoculum sizes were investigated.
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