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In-Depth Information
H
O
H
O
OH
H
O
OH
OH
O
O
O
O
H
O
H
O
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
OH
L
-Mannose
L
-Altrose
L
-Xylose
L
-Allose
[74]
[74]
[74]
[74]
OH
O
H
OH
OH
OH
OH
H
O
OH
OH
OH
H
O
H
O
OH
OH
OH
OH
OH
D
-Sorbitol
D
-Mannitol
D
-Arabitol
[74]
[74]
[74]
OH
O
H
O
H
O
OH
OH
O
OH
OH
H
O
OH
H
O
OH
H
O
OH
H
O
OH
H
O
OH
OH
OH OH
D
-Maltitol
D
-Xylitol
Myo-inositol
[74]
[74]
[74]
Fig. 3 (Continued)
from the glucan produced by the native strain in terms of solubility or
susceptibility to endo-dextranase hydrolysis.
76
Variants B-742CA and
B-742CB synthesized dextran with a-1,4 branched linkages and a high
percentage of a-1,3 bonds, respectively.
77
Mutants Lm M281 and Lm
M286 derived from L. mesenteroides strain Lm 28 were shown to produce
more active glucosyltransferases or resistant glucan, respectively.
78
Syn-
chrotron radiations in the 70-1000 eV region were also considered for
further engineering the Leuconostoc mesenteroides B-12FMC variant.
79
From this work, a hyperproducing mutant constitutive for dex-
transucrase, namely B-512FMCM, was shown to produce 13-fold increase
in activity and 1000-fold increase in glucansucrase protein compared to
the parental strain. UV radiations were also used to engineer the dex-
transucrase producing strain Leuconostoc mesenteroides KIBGE IB-22. One
mutant over the 42 generated showed a 6.75 fold increase in activity
compared to the wild-type enzyme.
80
Altogether, these results underline that genetic engineering of native
strains may be useful for both increasing the production of glucans and
modulating their properties.
2.2 Random engineering of recombinant enzymes
Because native strains may be sometimes dicult to handle, the use of
recombinant enzymes produced into well-known organisms such as
Escherichia coli has been investigated. Genes coding for glucansucrases
have been isolated, heterologously expressed and further considered for
bioengineering experiments. Ultrasoft X-ray irradiations have been
applied to an Escherichia coli transformant to generate dextransucrase
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