Biology Reference
In-Depth Information
when the internal ion content is high, whereas its steady-state activity cor-
responds to the external salinity, because the steady-state amount of internal
K
+
increases gradually in cells acclimated to increasing salinities (
Novak
et al., 2011
;
Reed et al., 1985
).
5. CYANOBACTERIAL BIOTECHNOLOGY AND SALT
ACCLIMATION
Due to environmental concerns and the future decline in oil produc-
tion, cyanobacteria are increasingly investigated as alternative sources for
green energy and chemical feedstock (e.g.
Ducat, Way, & Silver, 2011
). To
minimize competition with agricultural food production, the mass cultiva-
tion of cyanobacteria should be done on land not suited for agriculture and
by using salt water instead of freshwater. For this purpose, it is important
to gain more knowledge on salt acclimation of a broader set of cyanobac-
teria. Future production strains will be certainly optimized regarding salt-
tolerance mechanisms, i.e. by engineering the energetic cheapest strategy to
minimize negative impacts on product biosynthesis.
Compatible solutes will be not only important for enabling high growth
rates of production strains in salty media, these chemicals itself are of rela-
tively high value, because they can be used in cosmetics and pharmaceuti-
cals as moisturizers and stabilizers. Presently, GG (
Sawangwan et al., 2010
)
but particularly ectoine, a compatible solute from halobacteria, is produced
by the BITOP GmbH (
http://www.bitop.de/cms/website.php?id=/en/
terial milking process. It has been previously shown that the alternative
incubation in salt medium (production phase) and subsequent incubation
in distilled water (harvesting phase) could also be used to elute compatible
solutes from cyanobacteria (
Fulda, Hagemann, & Libbert, 1990
;
Reed, Warr,
Kerby, & Stewart, 1986
). Recently,
Synechococcus
sp. PCC 7942 strains have
been engineered, which express a sucrose export system. These strains did
not only continuously excrete sucrose into the culture supernatant when
grown in saline medium, the overall sucrose biosynthesis and photosynthesis
rate were also increased (
Ducat, Avelar-Rivas, Way, & Silver, 2012
).
ACKNOWLEDGEMENTS
The author wishes to thank all of my previous and current coworkers as well as co-operation
partners for the long and fruitful work on cyanobacterial salt acclimation. The work would
not have been possible without the continuous and generous support by the Deutsche
Forschungsgemeinschaft (DFG). The author thanks Dr I. Berman-Frank, Tel-Aviv, Israel, for
