Biology Reference
In-Depth Information
domains (
Pade et al., 2012
). Corresponding to the occurrence of the
otsAB
gene,
Crocosphaera
accumulates trehalose as only compatible solute. Overex-
pression of this gene in
E. coli
verified that the gene codes for a functional
trehalose biosynthesis enzyme. Interestingly,
C. watsonii
WH 8501 acquired
this gene by a lateral gene transfer event (
Pade et al., 2012
). Cyanobacteria
closely related to
Crocosphaera
usually accumulate GG, however, these genes
are missing (lost?) in this cyanobacterium.
3.3. Glucosylglycerol
Glucosylglycerol (GG; α-D-glucopyranosyl-(1 → 2)-glycerol) was the first
compatible solute, whose accumulation was found in a cyanobacterium
(
Borowitzka et al., 1980
). Later on, it was detected in many cyanobacte-
rial strains and was regarded to be characteristic for the group of moder-
ate halotolerance (
Hagemann, 2011
;
Reed, Borowitzka et al., 1986
). While
GG-accumulating beta-cyanobacteria are mostly euryhaline, i.e. they can be
cultivated in freshwater and salt-containing media (e.g.
Synechocystis
6803
or
Synechococcus
sp. PCC 7002;
Engelbrecht, Marin, & Hagemann, 1999
;
Marin, Zuther, Kerstan, Kunert, & Hagemann, 1998
), the GG-accumulating
picoplanktonic
Synechococcus
strains, which belong to the alpha-cyanobac-
teria, show only a small range of halotolerance, i.e. they can be cultivated
only in media near the normal seawater salinity level (
Klähn, Steglich et al.,
2010
). Beside its osmotic function, GG has good direct membrane and
protein stabilizing properties, which are also of biotechnological interest
(
Borges, Ramos, Raven, Sharp, & Santos, 2002
;
Hincha & Hagemann, 2004
;
Sawangwan, Goedl, & Nidetzky, 2010
).
Cyanobacteria use a two-step biosynthesis for GG (
Hagemann & Erdmann,
1994
) with an initial GG-phosphate synthase (GgpS) and a subsequent
GG-phosphate phosphatase (GgpP):
(GgpS) ADP-glucose + glycerol 3-phosphate → glucosylglycerol-
phosphate + ADP
(GgpP) Glucosylglycerol-phosphate → glucosylglycerol + Pi
This biosynthetic pathway is similar to that of sucrose, trehalose and glu-
cosylglycerate (
Klähn & Hagemann, 2011
). However, sucrose and trehalose
biosyntheses prefer UDP-glucose as glucosyl donor, while cyanobacterial
GG synthesis is strictly dependent on ADP-glucose (
Hagemann & Erdmann,
1994
;
Miao et al., 2003
). Many heterotrophic bacteria also accumulate GG
