Induction of L-lysine epsilon-aminotransferase by L-lysine in Streptomyces clavuligerus, producer of cephalosporins

L-Lysine epsilon-aminotransferase (LAT) catalyzes the first reaction in the two-step conversion of L-lysine (Lys) to 1-alpha-aminoadipic acid (Aaa), a direct precursor of cephalosporins (including cephamycin C) in Streptomyces clavuligerus. Previous work showed that addition of Lys to chemically defined medium improved antibiotic production. We show that in S. clavuligerus cultures supplemented with high concentrations of Lys, Lys enhances antibiotic production by a dual effect, i.e. as a substrate of LAT thus providing Aaa and also as an inducer of LAT yielding even more Aaa. On the other hand, LAT is not induced by Aaa.

Recombinant Acremonium chrysogenum strains for the industrial production of cephalosporin

Conventional strain improvement programs based on random mutagenesis and rational screening have meant valuable results to the antibiotic producing companies. The development of recombinant DNA techniques and their applications to the industrially-used cephalosporin-producing fungus Acremonium chrysogenum has provided a new tool, complementary to classical mutation, promoting the design of alternative biosynthetic pathways making it possible to obtain new antibiotics and to improve cephalosporin production. Yield increases have been achieved by increasing the dosage of the biosynthetic genes cefEF (deacetoxycephalosporin C expandase/hydroxylase) and cefG (deacetylcephalosporin C acetyltransferase) or enhancing the oxygen uptake by expressing a bacterial oxygen-binding heme protein (Vitreoscilla hemoglobin). New biosynthetic capacities such as the production of 7-aminocephalosporanic acid (7-ACA) or penicillin G have been achieved through the expression of the foreign genes dao (D-amino acid oxidase) coupled with cephalosporin acylase or penDE(acyl-CoA:6-APA acyltransferase) respectively. Confined manipulation of the above-mentioned recombinant strains must be performed according to standing rules.

Effect of oxygen on the respiratory system and cephalosporin-C production in Acremonium chrysogenum

In this paper in vivo studies on the overall and cyanide-resistant respiration of Acremonium chrysogenum in connection with different oxygen transfer rates are discussed. Two parameters of the cyanide-resistant respiration, the activity and the capacity were examined separately during cultivation together with the possibly respiration-influencing factors like NADH/NAD content and ADP-limitation. It was finally concluded that the cyanide-resistant respiration seems to be independent of the amount and proportion of oxidized/reduced coenzymes and not limited by ADP or phosphate, but it is strongly affected by the oxygen available. It was also established that the examined path must have an important role in cephalosporin-C overproduction.

Metabolic engineering of cephalosporin biosynthesis in Streptomyces clavuligerus

The biosynthesis of beta-lactams is one of the most thoroughly studied antibiotic pathways. The availability of the characteristics and the time profiles of activities of enzymes involved in the biosynthesis allows one to critically evaluate the potential rate-limiting steps in its production. Our approach to understanding the control of beta-lactam biosynthesis has been pursued using a two-stage strategy: (1) to predict the rate-limiting steps using a kinetic model and (2) to relax the rate-limiting steps by engineering the biosynthetic pathway or by altering the kinetic parameters of the predicted key rate-limiting enzyme. Kinetic analysis of the pathway dynamics of cephamycin C production in Streptomyces clavuligerus was performed using data obtained from wild type. Sensitivity analysis revealed that the availability of precursor alpha-aminoadipic acid and activity of ACV synthetase were the potential rate-limiting steps. Relaxation of the precursor limitation was accomplished by integration of an additional copy of the gene encoding lysine-epsilon-aminotransferase (lat) into the chromosome. The recombinant strain showed an increased level of cephamycin C production as expected. The intracellular levels of different intermediates in the pathway in batch cultures were analyzed.

Organization and expression in Pseudomonas putida of the gene cluster involved in cephalosporin biosynthesis from Lysobacter lactamgenus YK90

The Lysobacter lactamgenus YK90 pcbAB gene encoding delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (ACV) synthetase is located immediately upstream of the pcbC gene in the same orientation in the gene cluster involved in cephalosporin biosynthesis. The pcbAB gene encodes a large polypeptide composed of 3722 amino acid residues with a molecular mass of 411593 Da. The predicted amino acid sequence has a high degree of similarity with those of known ACV synthetases from fungi and actinomycetes. Within the pcbAB amino acid sequence, three conserved and repeated domains of about 600 amino acids were identified. the domains also share a high degree of similarity with non-ribosomal peptide synthetases such as gramicidin synthetase 2 of Bacillus brevis. The pcbAB gene was expressed under the control of the lac promoter in Pseudomonas putida. Expression of the gene cluster involved in cephalosporin biosynthesis in P. putida led to the accumulation of beta-lactam antibiotics. Deletion analysis of an open-reading frame located between the cefE and cefD genes from the gene cluster revealed that it encoded deacetylcephalosporin C synthetase (cefF). From the results presented here and those of previous studies, the genes involved in cephalosporin biosynthesis in L. lactamgenus appear to be clustered in the order pcbAB-pcbC- cefE-cefF-cefD-bla in the same orientation within a 17-kb region of DNA.

Molecular analysis of the gene cluster involved in cephalosporin biosynthesis from Lysobacter lactamgenus YK90

Determination of the nucleotide sequence downstream from the Lysobacter lactamgenus pcbC gene encoding isopenicillin N synthase revealed that five open-reading frames (ORF) including the pcbC gene were tightly linked in the same orientation. Each ORF has the remarkable feature of the protein-coding frame in the DNA sequence with a high G+C content. Expression in Escherichia coli and a comparison of the deduced amino acid sequences with published sequences showed that the gene cluster contained a deacetoxycephalosporin C synthetase (DAOCS) gene (cefE), an ORF having homology with the Cephalosporium acremonium DAOCS/deacetylcephalosporin C synthetase gene (cefEF), an isopenicillin N epimerase gene(cefD), and a beta-lactamase gene. The gene order was pcbC-cefE-ORF3-cefD-beta-lactamase.

Simulation of diauxic production of cephalosporin C by Cephalosporium acremonium: lag model for fed-batch fermentation

We extend a previously reported model (Chu, W.B.; Constantinides, A. Biotechnol. Bioeng. 1988, 32, 277-288) for the batch fermentation of cephalosporin C under the diauxic growth of Cephalosporium acremonium on glucose and sucrose to a fed-batch system. For this purpose, a novel lag model is proposed for diauxie, which has two functional forms, each embodying the dependence of lag on total cell mass and secondary substrate concentration. This lag model is applicable for batch simulations for arbitrary initial glucose and sucrose concentrations. We used the previously reported batch data to perform locally optimized fed-batch simulations. When applied to fed-batch fermentations, multiple lag times were accounted for. These studies showed that fed-batch fermentations (under the restriction that cell mass concentration did not exceed 25 g/L) could be more productive than simple batch runs. A representative result for a glucose-pulse fed-batch run at optimal cephalosporin production is a productivity of 4.22 mg of cephalosporin C/(L.h) and a yield of 9.25 mg of cephalosporin C/g of total sugar used.

Screening and characterization of microorganisms with glutaryl-7ADCA acylase activity

A screening of microorganisms producing glutaryl-7ADCA acylase, an enzyme able to hydrolyse glutaric acid selectively from glutaryl-3-deacetoxy-7-aminocephalosporanic acid (glutaryl-7ADCA), has been carried out in soil samples. Five microorganisms expressing acylase activity were isolated and classified as Bacillus cereus, Achromobacter xylosooxidans, Bacillus sp., Pseudomonas sp. and Pseudomonas paucimobilis. The screening was carried out by preparing enrichment cultures containing glutaryl-7-ADCA or cephalosporin C as the selective carbon source. Four model compounds (adipoyl-, glutamyl- and glutaryl-p-nitroanilide and glutarylcoumarin), mimicking the glutaryl-7ADCA beta-lactam moiety, were synthesized as substrates suitable for the rapid screening of the microorganisms (2500) isolated from the enrichment cultures. A total of 300 strains were active on the model substrates and only 5 displayed acylase activity on glutaryl-7ADCA. The fermentation parameters, such as pH and inducer concentration, for the optimal acylase expression and acylase specificity towards the model substrates were different for each strain.

A two-protein component 7 alpha-cephem-methoxylase encoded by two genes of the cephamycin C cluster converts cephalosporin C to 7-methoxycephalosporin C

Two genes, cmcI and cmcJ, corresponding to open reading frames 7 and 8 (ORF7 and ORF8) of the cephamycin C cluster of Nocardia lactamdurans encode enzymes that convert cephalosporin C to 7-methoxycephalosporin C. Proteins P7 and P8 (the products of ORF7 and ORF8 expressed in Streptomyces lividans) introduce the methoxyl group at C-7 of the cephem nucleus. Efficient hydroxylation at C-7 and transfer of the methyl group from S-adenosylmethionine require both proteins P7 and P8, although P7 alone shows weak C-7 hydroxylase activity and strong cephalosporin-dependent NADH oxidase activity. Both P7 and P8 appear to be synthesized in a coordinated form by translational coupling of cmcI and cmcJ. Protein P7 contains domains that correspond to conserved sequences in cholesterol 7 alpha-monooxygenases and to the active center of O-methyltransferases by comparison with the crystal structure of catechol-O-methyltransferase. Protein P8 may act as a coupling protein for efficient hydroxylation at C-7 in a form similar to that of the two-component system of Pseudomonas putida p-hydroxyphenylacetate-3-hydroxylase.

Genes for beta-lactam antibiotic biosynthesis

The genes pcbAB, pcbC and penDE encoding enzymes involved in the biosynthesis of penicillin have been cloned from Penicillium chrysogenum and Aspergillus nidulans. They are clustered in chromosome I (10.4 Mb) of P. chrysogenum, but they are located in chromosome II of Penicillium notatum (9.6 Mb) and in chromosome VI (3.0 Mb) of A. nidulans. Expression studies have shown that each gene is expressed as a single transcript from separate promoters. Enzyme regulation studies and gene expression analysis have provided useful information to understand the control of gene expression leading to overexpression of the genes involved in penicillin biosynthesis. Cephalosporin genes have been studied in Cephalosporium acremonium and also in cephalosporin-producing bacteria. In C. acremonium the genes involved in cephalosporin biosynthesis are separated in at least two clusters. Cluster I (pcbAB-pcbC) encodes the first two enzymes of the cephalosporin pathway which are very similar to those involved in penicillin biosynthesis. Cluster II (cefEF-cefG), encodes the last three enzymatic activities of the cephalosporin pathway. It is unknown, at this time, if the cefD gene encoding isopenicillin epimerase is linked to any of the two clusters. In cephamycin producing bacteria the genes encoding the entire biosynthetic pathway are located in a single cluster extending for about 30 kb in Nocardia lactamdurans, and in Streptomyces clavuligerus. The cephamycin clusters of N. lactamdurans and S. clavuligerus include a gene lat which encodes lysine-6-aminotransferase an enzyme involved in formation of the precursor alpha-aminoadipic acid. The N. lactamdurans cephamycin cluster includes, in addition, a beta-lactamase (bla) gene, a penicillin binding protein (pbp), and a transmembrane protein gene (cmcT) that is probably involved in secretion of the cephamycin. Little is known however about the mechanism of control of gene expression in the different beta-lactam producers. The availability of most of the structural genes provides a good basis for further studies on gene expression. This knowledge should lead in the next decade to a rational design of strain improvement procedures. The origin and evolution of beta-lactam genes is intriguing since their nucleotide sequences are extremely conserved despite their restricted distribution in the microbial world.

Production of cephalosporin intermediates by feeding adipic acid to recombinant Penicillium chrysogenum strains expressing ring expansion activity

We demonstrate a novel and efficient bioprocess for production of the cephalosporin intermediates, 7-aminocephalosporanic acid (7-ACA) or 7-amino deacetoxycephalosporanic acid (7-ADCA). The Streptomyces clavuligerus expandase gene or the Cephalosporium acremonium expandase-hydroxylase gene, with and without the acetyltransferase gene, were expressed in a penicillin production strain of Penicillium chrysogenum. Growth of these transformants in media containing adipic acid as the side chain precursor resulted in efficient production of cephalosporins having an adipyl side chain, proving that adipyl-6-APA is a substrate for either enzyme in vivo. Strains expressing expandase produced adipyl-7-ADCA, whereas strains expressing expandase-hydroxylase produced both adipyl-7-ADCA and adipyl-7-ADAC (aminodeacetylcephalosporanic acid). Strains expressing expandase-hydroxylase and acetyltransferase produced adipyl-7-ADCA, adipyl-7-ADAC and adipyl-7-ACA. The adipyl side chain of these cephalosporins was easily removed with a Pseudomonas-derived amidase to yield the cephalosporin intermediates.

Possible involvement of the lysine epsilon-aminotransferase gene (lat) in the expression of the genes encoding ACV synthetase (pcbAB) and isopenicillin N synthase (pcbC) in Streptomyces clavuligerus

Streptomyces clavuligerus produces the beta-lactam antibiotics penicillin N, O-carbamoyldeacetylcephalosporin C and cephamycin C. We characterized a wild-type DNA region which restores antibiotic formation to a mutant strain named NP1, previously shown to exhibit depressed activities for two early enzymes of cephalosporin synthesis, delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS) and isopenicillin N synthase (IPNS). L-Lysine epsilon-aminotransferase (LAT) assays and alpha-AAA feeding experiments suggested that strain NP1 is a lat mutant. NP1 recovered LAT, ACVS and IPNS activities when transformed with the cloned region. DNA sequencing showed that this region encodes the entire LAT gene (lat), required for the conversion of L-lysine to the beta-lactam precursor L-alpha-aminoadipic acid (alpha-AAA), as well as the upstream half of the ACVS gene (pcbAB). The activities of ACVS and IPNS appear to depend upon LAT expression. Gene fusions constructed to investigate promoter activities in the cloned region support a model of interdependence in the expression of the genes for LAT, ACVS and IPNS (pcbC).

Expression studies with the bidirectional pcbAB-pcbC promoter region from Acremonium chrysogenum using reporter gene fusions

Two cephalosporin genes from Acremonium chrysogenum, pcbAB and pcbC encode the ACV (alpha-aminoadipyl-cysteinyl-valine) synthetase and isopenicillin N-synthetase, respectively. The two adjacent genes are orientated in opposite directions on the chromosomal DNA, separated by a 1.2-kb non-translated sequence, carrying the putative promoter sequences. Complete sequencing of this intergenic region revealed differences from homologous sequences from other strains. To assess the putative promoter strength, we constructed an expression vector carrying the beta-glucuronidase (gusA) and beta-galactosidase (lacZ) genes in opposite orientation. Fusion of the pcbAB-pcbC promoter region resulted in recombinant vector molecules, which were used for in-vivo expression studies. Using the co-transformation procedure, the reporter gene fusions were transferred into A. chrysogenum recipient strains together with vector pMW1. Individual transformants were used for protein preparations to measure specific activities of the enzymes coded by the reporter genes. The data provide in-vivo evidence that the pcbC promoter is at least five times stronger than the pcbAB promoter. Our approach should prove useful in evaluating regulatory sequences that govern gene expression in A. chrysogenum.

[Role of biocatalysis in the creation and improvement of production of beta-lactam antibiotics in Russia]

The paper presents the results of the studies carried out by the authors within 20 years on development of processes for production of beta-lactam antibiotics with using biocatalysis. The proposed general principles for the development of efficient biocatalytic technologies are discussed in regard to production of the key compounds and synthesis of beta-lactams. The paper includes 4 parts concerned with comparison of the biocatalytic and chemical processes for production of beta-lactam antibiotics, requirements to the quality of the biocatalysts used and criteria for estimation of the efficiency of the stage of the technological biocatalyst production. The criteria provided determination of the optimal biocatalyst for production of the key compounds in the synthesis of beta-lactams. A retrospective analysis of the biocatalytic processes for production of 6-amino-penicillanic acid is presented and the impact of the activity and the form of the biocatalyst on the process efficiency is substantiated. Various schemes of the enzymatic synthesis of beta-lactam antibiotics and the approaches to the improvement of the technological processes including those with the use of immobilized microbial cultures at the stage of the production of the initial biosynthetic antibiotics are described. The prospects for the improvement of the processes for production of drugs with the use of biocatalysis are indicated and the main trends of the research required for the large scale use of the immobilized enzymes, microbial cells, oligo-enzymatic and poly-enzymatic systems in transformation and synthesis of organic compounds are defined.

A role for alanine in the ammonium regulation of cephalosporin biosynthesis in Streptomyces clavuligerus

It is known that excess ammonium supply decreases cephalosporin production and represses cephalosporin synthases. We wondered whether an additional important effect could be inhibition of synthase action by alanine. We had previously shown that ammonium addition induced alanine dehydrogenase and increased intracellular alanine and that alanine could inhibit resting cell synthesis of cephalosporins. In the present work we confirm the alanine inhibition of antibiotic production by resting cells. We found L-alanine inhibited three of the four synthases tested: ACV synthetase, cyclase and expandase; the epimerase was not inhibited. These data suggest that interference in cephalosporin production by growth in ammonium salts involves synthase inhibition by intracellular alanine, in addition to the known role of ammonium in synthase repression.

Improved expression of a hybrid Streptomyces clavuligerus cefE gene in Penicillium chrysogenum

A hybrid cefE gene, encoding penicillin N expandase, was constructed by fusing the promoter sequences, Pcp, and terminator sequences, Pct from the Penicillium chrysogenum pcbC gene to the open reading frame (orf), cefEorf, from the Streptomyces clavuligerus cefE gene. The resulting hybrid gene, Pcp/cefE'orf/Pct, differed from a previously reported hybrid cefE gene contained on plasmid pPS65. The latter gene, Pcp/cefE'orf/Sct, contained the Pcp sequences fused to the S. clavuligerus cefE orf still attached to the S. clavuligerus terminator sequences, Sct. The new hybrid gene was transformed into P. chrysogenum on plasmid vector pRH6. Transformants were selected by phleomycin resistance conferred by a hybrid ble gene present on plasmid pRH6. The hybrid ble gene was formed by attaching Pcp sequences to the ble orf. Among transformants obtained with pRH6, one exhibited a 70-fold higher level of activity of penicillin N expandase than the best transformant previously obtained from a 10-fold larger population of pPS65 transformants. The penicillin N expandase activity in pRH6 transformant, 9EN-5-1, was fourfold higher than the activity in the S. clavuligerus strain used as the source of the cefE orf and 75% of the activity observed in an industrial strain of Cephalosporium acremonium. Sequencing of the junctions of the heterologous DNA in Pcp/cefEorf/Pct uncovered a modification of the cefE open reading frame introduced during construction of the hybrid gene; the modified open reading frame is designated cefE'orf.

Interdependence of gene expression for early steps of cephalosporin synthesis in Streptomyces clavuligerus

The early steps of cephamycin synthesis by S. clavuligerus are catalyzed sequentially by lysine epsilon-aminotransferase (LAT), delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase (ACVS) and isopenicillin N synthase (cyclase, IPNS). The genes (lat, pcbAB, and pcbC, respectively) are closely linked in the same order as the enzymes act in the biosynthetic pathway and are transcribed in the same direction. Four cephamycin non- (or low-) producing mutants are pleiotropic in that they have undetectable or markedly diminished levels of ACVS and cyclase; two mutants almost completely lack LAT activity. All four mutants are complemented in cephamycin formation by transformation with pNBR1, a plasmid containing a 7.2-kb genomic region of S. clavuligerus in vector pIJ702. The cloned DNA was found to possess no part of the cyclase gene, but instead it contained lat and the 5' upstream part of pcbAB. Doran et al. reported that the 31-bp region between pcbAB and pcbC contains no recognizable promoter or transcription termination sequences. We found that there are 153 bp between the lat ORF and the pcbAB start codon. A potential transcriptional terminator begins 4 to 6 bp downstream of the lat ORF. In the 111-bp segment between the end of the "terminator" and the pcbAB start codon, there are no Streptomyces-like or Escherichia coli-like promoter consensus sequences. However, upstream of the "terminator," that is, in the downstream portion of the lat ORF, are two regions resembling a Streptomyces consensus promoter. Promoter activity in gene fusion constructions was demonstrated in this region. A third potential promoter is upstream of the lat ORF, but only the--10 part is on the cloned DNA. The mechanism by which the cloned DNA (containing lat, the 5' part of pcbAB, and the intervening sequence) influences the expression of the downstream genes encoding ACVS and IPNS, even in strains that possess LAT activity, is an intriguing target of future investigation.

Exogenous methionine increases levels of mRNAs transcribed from pcbAB, pcbC, and cefEF genes, encoding enzymes of the cephalosporin biosynthetic pathway, in Acremonium chrysogenum

Methionine stimulated cephalosporin production in cultures of three different strains of Acremonium chrysogenum when added either at inoculation time or at 72 h to cells grown previously in the absence of methionine. When methionine was added at 72 h, the stimulation of cephalosporin biosynthesis was observed only 12 h later and required de novo protein synthesis. Methionine increased the levels of enzymes (isopenicillin N synthase and deacetylcephalosporin C acetyltransferase) expressed from genes (pcbC and cefG, respectively) located in the two clusters of cephalosporin biosynthesis genes in the wild-type A. chrysogenum strain and also in the two improved strains, CW19 and C10. Methionine-supplemented cells showed higher levels of transcripts of the four known genes (pcbAB, pcbC, cefEF and, to a slight extent, cefG) of the cephalosporin biosynthetic pathway than cells grown in the absence of methionine. The levels of the cefG transcript were much lower than those of the pcbAB, pcbC, and cefEF transcripts. The induction by methionine of transcription of the four cephalosporin biosynthesis genes and the known effect of this amino acid on the differentiation of A. chrysogenum indicate that methionine exerts a pleiotropic effect that coordinately regulates cephalosporin biosynthesis and differentiation.

Expression of genes and processing of enzymes for the biosynthesis of penicillins and cephalosporins

The genes pcbAB, pcbC and penDE encoding the enzymes (alpha-aminoadipyl-cysteinyl-valine synthetase, isopenicillin N synthase and isopenicillin N acyltransferase, respectively) involved in the biosynthesis of penicillin have been cloned from Penicillin chrysogenum and Aspergillus nidulans. They are clustered in chromosome I (10.4 Mb) of P. chrysogenum, in chromosome II of Penicillium notatum (9.6 Mb) and in chromosome VI (3.0 Mb) of A. nidulans. Each gene is expressed as a single transcript from separate promoters. Enzyme regulation studies and gene expression analysis have provided useful information to understand the control of genes involved in penicillin biosynthesis. The enzyme isopenicillin N acyltransferase encoded by the penDE gene is synthesized as a 40 kDa protein that is (self)processed into two subunits of 29 and 11 kDa. Both subunits appear to be required for acyl-CoA 6-APA acyltransferase activity. The isopenicillin N acyltransferase was shown to be located in microbodies, whereas the isopenicillin N synthase has been reported to be present in vesicles of the Golgi body and in the cell wall. A mutant in the carboxyl-terminal region of the isopenicillin N acyltransferase lacking the three final amino acids of the enzymes was not properly located in the microbodies and failed to synthesize penicillin in vivo. In C. acremonium the genes involved in cephalosporin biosynthesis are separated in at least two clusters. Cluster I (pcbAB-pcbC) encodes the first two enzymes (alpha-aminoadipyl-cysteinyl) valine synthetase and isopenicillin N synthase) of the cephalosporin pathway which are very similar to those involved in penicillin biosynthesis. Cluster II (cefEF-cefG), encodes the last three enzymatic activities (deacetoxycephalosporin C synthetase/hydroxylase and deacetylcephalosporin C acetyltransferase) of the cephalosporin pathway. It is unknown, at this time, if the cefD gene encoding isopenicillin epimerase is linked to any of these two clusters. Methionine stimulates cephalosporin biosynthesis in cultures of three different strains of A. chrysogenum. Methionine increases the levels of enzymes (isopenicillin N synthase and deacetylcephalosporin C acetyltransferase) expressed from genes (pcbC and cefG respectively) which are separated in the two different clusters of cephalosporin biosynthesis genes. This result suggests that both clusters of genes have regulatory elements which are activated by methionine. Methionine-supplemented cells showed higher levels of transcripts of the pcbAB, pcbC, cefEF genes and to a lesser extent of cefG than cells grown in absence of methionine. The levels of the cefG transcript were very low as compared to those of pcbAB, pcbC and cefEF.(ABSTRACT TRUNCATED AT 400 WORDS)

The production of cephalosporin C by Acremonium chrysogenum is improved by the intracellular expression of a bacterial hemoglobin

A DNA vector for expressing an oxygen-binding heme protein (Vitreoscilla hemoglobin, or VHb) in filamentous fungi was constructed and introduced into a cephalosporin C-producing strain of Acremonium chrysogenum. Expression of VHb in transformants was demonstrated by Western immunoblot analysis and by increased carbon monoxide binding activity of cell extracts. Several VHb-expressing transformants produced significantly higher yields of cephalosporin C than control strains in batch culture experiments. Using the same vector system, VHb was also expressed in the related fungus Penicillium chrysogenum.

The enzymes involved in biosynthesis of penicillin and cephalosporin; their structure and function

The biosynthetic pathway resulting in the penicillins and cephalosporins contains two Fe2+ oxidase enzymes which are responsible for the conversion of alpha-aminoadipoyl-L-cysteinyl-D-valine into isopenicillin N and penicillin N into deacetoxycephalosporin C. We will discuss the studies delineating the ligand binding of these enzymes and present a possible secondary structure.

Enzymatic oxidation of cephalosporin C using whole cells of the yeast Triginopsis variabilis within a "cross-flow filter-reactor"

An economical process for the enzymatic oxidation of cephalosporin C to glutaryl-7-ACA was developed at a pilot plant scale. The process utilized nonviable whole cells of the yeast Triginopsis variabilis containing high levels of D-amino acid oxidase. Prior to use, the whole cells were permeabilized with a 25% acetone/water solution which enhanced their apparent activity by 20- to 50-fold. After permeabilization, the whole cells were incubated at pH 11, which served to selectively deactivate catalase which was present in very large quantities. Deactivation of catalase was critical to achieving high reaction yields. The whole cells were utilized within a "cross-flow filter-reactor" which allowed easy and economical recycle of the cells for repeated use. The overall yield of glutaryl-7-ACA from cephalosporin C was 90-95%. The overall productivity of the yeast was 13 kg cephalosporin C oxidized per kilogram yeast (dry basis). The reaction was run at a concentration of 40 g cephalosporin CL-1 and the overall reactor productivity was 11 g glutaryl-7-ACA l-1 h-1. The process has been thoroughly demonstrated on a 35-l scale, and it should be directly scaleable to 10,000 l or more.