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Figure 6. Distribution of G-blocks in alginates from
M. pyrifera
(white),
D.
potatorium
(gray) and
L. hyperborea
stipe (black). Adapted from Aarstad et al.
(2012), Biomacromolecules, 13, 106-116.
1.2.6. Bacterial alginates:
Bacterial alginates can in principle be produced by fermentation (
A. vinelandii,
P. aeruginosa
and other Pseudomonads), but is currently complicated and
non-profitable because the bacteria produce alginate-degrading enzymes
(lyases). In contrast, xanthan is an industrially important bacterial
polysaccharide produced by large-scale fermentation.
F
G
F
M
F
GG
F
MG
(F
GM
)
F
MM
F
GGG
F
MGM
F
GGM
N
G>1
Remarks
Pseudomonas
aeruginosa
0.00
9
0.04 -
0.10
1.00
0.90 -
0.96
-
-
-
0.04 -
0.10
1.00
0.90
-
0.96
-
-
-
0.04 -
0.10
-
-
-
-
O-
acetylated
Azotobacter
vinelandii
0.45 0.55 0.42 0.03
0.52
O-
acetylated
(22%)
The alginates from wild type
Pseudomonas
species have generally low
contents of L-guluronic acid, typically F
G
is in the range 0.04 – 0.10.
Moreover, these G residues are single residues (MGM type). Hence, no G-
blocks are found in these alginates.
In recent years epimerase-negative mutants of
Pseudomonas
have been
developed, enabling production of mannuronan (F
G
=0), which is a starting
point for in vitro epimerization for tailoring of alginates with sequences not
found in nature. Such alginates are extremely important tools for elucidating
the complex structure-function relationships in alginates.
9
Top mutant, bottom: wild types
Ultralong G-blocks
DP of G-block obtained by HPAEC-PAD