Biomedical Engineering Reference
In-Depth Information
(7-ACA), which can be derived enzymatically or chemically from
cephalosporin C or penicillin G. An alternative to classical strain
improvement consists of genetic manipulation of the microorganism
of interest to divert or modify the biosynthetic pathways, including
heterologous expression in related fungi or even in yeasts. Based on this,
we can clasify cephalosporins as (i)
P. chrysogenum
-derived cephalosporins
and (ii)
A. chrysogenum
-derived cephalosporins.
P. chrysogenum
-derived Cephalosporins
The penicillin-derived cephalosporins are mainly based on 7-ADCA,
which is produced after the chemical expansion of the benzylpenicillin
ring (yielding phenylacetyl-7-ADCA) followed by a enzymatic deacylation
that removes the aromatic side chain (Barber et al. 2004)
(Fig. 4).
Due
to the cost, complexity and pollution of the chemical ring expansion
process, other method for the production of 7-ADCA is desirable, such
as the genetic engineering of
P. chrysogenum
(it cannot naturally produce
cephalosporins). The high capacity of
P. chrysogenum
to produce antibiotics
together with the higher costs derived from
A. chrysogenum
fermentations,
have promoted the production of cephalosporanic ring-derived antibiotics
in
P. chrysogenum
. This fungus has been genetically modifi ed to express
different combinations of the cephalosporin biosynthetic genes obtained
from cephalosporin or cephamycin-producer microorganisms. When the
cefE
gene from
S. clavuligerus
or the
cefEF
gene of
A. chrysogenum
were
introduced in
P.chrysogenum
, the transformant was capable of expanding
the penicillin thiazolidine ring to a six-membered dihydrothiazine ring.
Feeding adipic acid as a side-chain precursor resulted in the production
of adipyl-6-APA easily expanded to adipyl-7-ADCA (Fig. 4). This strategy
also leads to the production of adipyl-7-ACA if the acetyltransferase gene
(
cefG
) is also introduced. Similarly, introduction of the
cefEF
gene from
A.chrysogenum
and the
cmcH
gene encoding a carbamoyl transferase of
S. clavuligerus
in
P. chrysogenum
, yielded ad7-ACCCA (adipoyl-7-amino-
3-carbamoyloxymethyl-3-cephem-4-carboxylic acid), which is a stable
semisynthetic cephalosporin precursor (Harris et al. 2009).
A. chrysogenum
-derived Cephalosporins
The previous biological routes for the production of 7-ADCA have been
developed in the penicillin producer fungus
P. chrysogenum
, basically
because early attempts to produce 7-ADCA in
A. chrysogenum
after
inactivation of the hydroxylase (but retaining the expandase) activity of the
cefEF
gene, were unsuccessful. However, the production of 7-ADCA in
A.
