Perspectives on Chemicals from Renewable Resources - Sustainable Biotechnology: Sources of Renewable Energy - page 202

exponential to stationary phase in the cell and is accumulated (at neutral pH) within
the cytoplasm as insoluble cyanophycin granular peptide (CGP), Fig. 3.
The enzyme cyanophycin synthetase (CphA) [19] is responsible for the
non-ribosomal biosynthesis, binding L-aspartic acid with L-arginine to form
cyanophycin. However, slow growth of cyanobacteria and the low cyanophycin con-
tent means that efficient production of significant amounts are unattained. However
CphA genes that have been cloned and expressed in bacteria, such as Escherichia
coli, have lead to higher cell dry matter when cultivation was carried out in high
quality (and thus expensive) media [20]. During the last years more interest has
been directed towards cyanophycin as an interesting source for a number of appli-
cations. For example cyanophycin may be chemically treated in order to obtain a
material with low (or reduced) arginine content [21]. This material has the prop-
erties of poly(aspartic acid) which could allow it to be used as a bio-derived and
therefore biodegradable alternative to poly(acrylic acid). More recently it has been
proposed that CGP could be used as a source of aspartic acid and arginine, which
has a rich chemistry that could lead to the production of a number of commer-
cially interesting compounds [22]. This will be dealt with in more detail later. Thus
the production of cyanophycin could be used to accumulate, concentrate and iso-
late aspartic acid and arginine to obtain them for use as raw materials in chemical
synthesis.
However production using CphA is constrained by the availability of the aspar-
tic acid and in particular arginine. Thus for reasonable production these should be
added to the growth media, consequently reducing the economic feasibility unless
an inexpensive source of these amino acids is found. The potato juice concentrate,
Protamylasse R , a rest stream obtained from the processing of potatoes to produce
starch contains organic acids, sugars and minerals as well as peptides and amino
acids including high levels of aspartic acid and arginine making it a particularly
appealing and inexpensive production media or component [23].
Indeed it was shown that when using E. coli increasing the amount of protamy-
lasse in the media increased not only the cell dry matter (CDM) but also the % of
CGP in the CDM [24]. Amaximum was reached at ca. 5% (vol/vol) Protamylasse R .
These results were significantly better than those obtained when Acinetobacter and
P. putida were used.
For the isolation from the fermentation media, of it has been described that CGP
may be dissolved in acidic aqueous media. Using this approach allows separation
from cell debris. Readjusting the pH to 7 allows precipitation and isolation of the
CGP [20]. Such an acid extraction method of CGP was found to be more effective
than previously reported methods [25] which were more cumbersome.
Once the CGP is obtained it may then be reacted to reduce (or remove) the argi-
nine side chains or used as a source of aspartic acid and arginine. Both these amino
acids due to their functionality and carbon chain length possibilities to be used
as raw materials for products that are traditionally prepared in the petrochemical
industry.