Discussion
The characteristics of selected alkalophilic
bacteria isolate #10 were studied. Even though no
spore was found inside the bacterial cells, its
biochemical characteristics were identical to those of
Bacillus sp. described by Gee et al. (1980). We
designated the selected bacteria as Bacillus sp. #10.
The optimal conditions for CGTase production were
studied including substitution of different starch as
carbon source and CGTase inducer, concentration of
starch, and temperature. It was found that rice and
sticky rice starch were the most effective carbon
sources of Bacillus sp. #10 for enzyme production
at a concentration of 1% (w/v) (Table 1). The
optimal temperature for cultivation was 37
o
C (Table
4). Furthermore, CGTase synthesis of Bacillus sp.
#10 started from the early exponential phase and maximal CGTase activity was found at stationary
phase at 120 h (Table 6). These results are in
agreement with the culture characteristic of Bacillus
circulans (Nakamura and Horikoshi, 1976; Paloheimo
et al., 1992) and Bacillus stearothermophilus
(Stefanova et al., 1999) which exhibited maximum
activity after 48-50 h of growth. The optimal
temperature for enzyme-catalyzed reaction was
50
o
C (Table 1). The sticky rice starch was also the
most effective substrate for enzyme activity at a
concentration of 4% (w/v) (Table 6). We have
improved the CGTase production by alkalophilic
Bacillus sp. #10 from 1:2
4
to 1:2
8
dilution limit of
CGTase/CD-TCE activity assay when sticky rice
was used as carbon source at 1% (w/v) and
substrate at 4% (w/v) (Table 1, 6). The alkalophilic
Bacillus sp. #10 produced only β -CD (Figure 2)