Targeted inactivation of the mecB gene, encoding cystathionine-gamma-lyase, shows that the reverse transsulfuration pathway is required for high-level cephalosporin biosynthesis in Acremonium chrysogenum C10 but not for methionine induction of the cephalosporin genes

Targeted gene disruption efficiency in Acremonium chrysogenum was increased 10-fold by applying the double-marker enrichment technique to this filamentous fungus. Disruption of the mecB gene by the double-marker technique was achieved in 5% of the transformants screened. Mutants T6 and T24, obtained by gene replacement, showed an inactive mecB gene by Southern blot analysis and no cystathionine-gamma-lyase activity. These mutants exhibited lower cephalosporin production than that of the control strain, A. chrysogenum C10, in MDFA medium supplemented with methionine. However, there was no difference in cephalosporin production between parental strain A. chrysogenum C10 and the mutants T6 and T24 in Shen's defined fermentation medium (MDFA) without methionine. These results indicate that the supply of cysteine through the transsulfuration pathway is required for high-level cephalosporin biosynthesis but not for low-level production of this antibiotic in methionine-unsupplemented medium. Therefore, cysteine for cephalosporin biosynthesis in A. chrysogenum derives from the autotrophic (SH(2)) and the reverse transsulfuration pathways. Levels of methionine induction of the cephalosporin biosynthesis gene pcbC were identical in the parental strain and the mecB mutants, indicating that the induction effect is not mediated by cystathionine-gamma-lyase.     

Expression of the transporter encoded by the cefT gene of Acremonium chrysogenum increases cephalosporin production in Penicillium chrysogenum

By introduction of the cefEF genes of Acremonium chrysogenum and the cmcH gene of Streptomyces clavuligerus, Penicillium chrysogenum can be reprogrammed to form adipoyl-7-amino-3-carbamoyloxymethyl-3-cephem-4-carboxylic acid (ad7-ACCCA), a carbamoylated derivate of adipoyl-7-aminodeacetoxy-cephalosporanic acid. The cefT gene of A. chrysogenum encodes a cephalosporin C transporter that belongs to the Major Facilitator Superfamily. Introduction of cefT into an ad7-ACCCA-producing P. chrysogenum strain results in an almost 2-fold increase in cephalosporin production with a concomitant decrease in penicillin by-product formation. These data suggest that cephalosporin production by recombinant P. chrysogenum strains is limited by the ability of the fungus to secrete these compounds.     

Gene organization and plasticity of the β-lactam genes in different filamentous fungi

The genes pcbAB, pcbC and penDE encoding enzymes that catalyze the three steps of the penicillin biosynthesis have been cloned from Penicillium chrysogenum and Aspergillus nidulans. They are located in a cluster in Penicillium chrysogenum, Penicillium notatum, Aspergillus nidulans and Penicillium nalgiovense. The three genes are clustered in chromosome I (10.4 Mb) of P. chrysogenum, in chromosome II of P. notatum (9.6 Mb) and in chromosome VI (3.0 Mb) of A. nidulans. The cluster of the penicillin biosynthetic genes is amplified in strains with high level of antibiotic production. About five to six copies of the cluster are present in the AS-P-78 strain and 11 to 14 copies in the E1 strain (an industrial isolate), whereas only one copy is present in the wild type (NRRL 1951) strain and in the low producer Wis 54-1255 strain. The amplified region in strains AS-P-78 and E1 is arranged in tandem repeats of 106.5 or 57.6-kb units, respectively. In Acremonium chrysogenum the genes involved in cephalosporin biosynthesis are separated in at least two clusters. The pcbAB and pcbC genes are linked in the so-called early cluster of genes involved in the cephalosporin biosynthesis. The late cluster, which includes the cefEF and cefG genes, is involved in the last steps of cephalosporin biosynthesis. The early cluster was located in chromosome VII (4.6 Mb) in the C10 strain and the late cluster in chromosome I (2.2 Mb). Both clusters are present in a single copy in the A. chrysogenum genome, in the wild-type and in the high cephalosporin-producing C10 strains.     

Coordinate increase of isopenicillin N synthetase, isopenicillin N epimerase and deacetoxycephalosporin C synthetase in a high cephalosporin-producing mutant of Acremonium chrysogenum and simultaneous loss of the three enzymes in a non-producing mutant

Abstract An early blocked mutant in cephalosporin biosynthesis ( Acremonium chrysogenum N₂) had simultaneously lost 3 enzymes of the cephalosporin biosynthetic pathway (isopenicillin N synthetase, isopenicillin N epimerase and deacetoxycephalosporin C synthetase) and accumulated the tripeptide α-aminoadipyl-cysteinyl-valine. An overproducing mutant ( A. chrysogenum C-10) showed a 2-fold increase in the same 3 enzymes throughout fermentation, with respect to the low-producing strain A. chrysogenum CW-19. These results suggest that expression of the genes coding for cephalosporin biosynthetic enzymes is altered in a coordinate form in these mutants.     

Cloning, sequence analysis and transcriptional study of the isopenicillin N synthase of Penicillium chrysogenum AS-P-78

A gene (ips) encoding the isopenicillin N synthase of Penicillium chrysogenum AS-P-78 was cloned in a 3.9 kb SalI fragment using a probe corresponding to the amino-terminal end of the enzyme. The SalI fragment was trimmed down to a 1.3 kb NcoI-BglII fragment that contained an open reading frame of 996 nucleotides encoding a polypeptide of 331 amino acids with an Mr of 38012 dalton. The predicted polypeptide encoded by the ips gene of strain AS-P-78 contains a tyrosine at position 195, whereas the gene of the high penicillin producing strain 23X-80-269-37-2 shows an isoleucine at the same position. The ips gene is expressed in Escherichia coli minicells using the lambda phage PL promoter. Some similar sequence motifs were found in the upstream region of the ips gene of P. chrysogenum when compared with the upstream sequences of the ips genes of Cephalosporium acremonium and Aspergillus nidulans. Primer extension studies indicated that the start of the mRNA coincides with a T in position -11 which is located in a conserved pyrimidine-rich sequence, near two CAAG boxes. Clones of P. chrysogenum Wis 54-1255 transformed with the ips gene showed a five-fold higher isopenicillin N synthase activity than the untransformed cultures.