Biomedical Engineering Reference
In-Depth Information
provide an excellent overview on structure-function relationships of glucansucrases
and fructansucrase [
80,
81,
100
] .
HoPS produced from sucrose are composed only of fructose or glucose but never-
theless have a large diversity with respect to linkage type, or degree of branching, and
molecular weight. Dextran is mainly composed of a −(1
→
6) linked glucose molecules
with a varying degree of a −(1
3,6) branching
points. Dextran is produced by many strains of
Leuconostoc
spp. and
Weissella
spp.
but dextran-forming
Lactobacillus
spp. were also described [
80,
81,
88
] . Mutan is
mainly composed of a −(1
→
3) or a −(1
→
2) linkages and a −(1
→
3) linked glucose moieties and is produced by
Streptococcus
spp. and
L. reuteri
[
80,
81
] . Glucans with alternating a −(1
→
→
6) and
a −(1
6) linkages are referred to as alternan
and reuteran, respectively. Reuteran formation has to date exclusively been observed
in strains of
L. reuteri
[
81
]. The current knowledge on structure-function relationships
of glucansucrases allows the manipulation of the linkage type [
101
] as well as the
molecular weight and degree of branching [
102
] . Information on structure-function
relationships of glucansucrases has also been used for identification of wild-type glu-
cansucrases producing polymers with desired properties [
103
]. The linkage type in the
oligosaccharides formed by glucansucrases generally matches the linkage types found
in the corresponding polysaccharide [
81,
97
] . For example,
L. reuteri
121 produces
a −(1
→
3) or alternating a −(1
→
4) and a −(1
→
6) linked reuteran with a relative molecular weight of 8 × 10
7
;
in the presence of glucose or maltose as acceptor carbohydrates, maltose and isomalt-
ose or isomaltotriose and panose are produced. Fructans produced by lactic acid bac-
teria include the predominantly b −(2
→
4) and a −(1
→
→
1) linked inulin and the predominantly
a −(2
6) branching points [
80,
81,
98,
104
]. A majority of fructan-producing sourdough isolates form levan.
Remarkably, levansucrases form predominantly inulin-type fructo-oligosaccharides
and hetero-oligosaccharides from sucrose [
95,
98
] .
→
6) linked levan; both polymers contain b −(2
→
1
→
7.5.2
Ecological Function of HoPS Production and HoPS
Formation in Dough
The ecological function of glucansucrases and fructansucrases for cereal-associated
lactic acid bacteria was related to biofilm formation, sucrose and raffinose utilization,
and stress resistance. In oral streptococci, glucansucrases and fructansucrases are
primarily responsible for sucrose-dependent biofilm formation on the tooth enamel,
and are considered major virulence factors of these organisms [
105
] . Analogous to
the biofilm formation by oral streptococci, colonization and biofilm formation by
L. reuteri
in nonsecretory epithelia of the proximal intestinal tract of animals was
found to be dependent on HoPS formation. The reuteransucrase of
L. reuteri
TMW1.106 was a major contributor to formation of the extracellular biofilm matrix,
the levansucrase in the same organism functions as a glucan-binding protein. Both
enzymes are required for colonization of reconstituted lactobacilli-free mice by
L. reuteri
TMW 1.106 [
106
] .
