The cefG gene of Cephalosporium acremonium is linked to the cefEF gene and encodes a deacetylcephalosporin C acetyltransferase closely related to homoserine O-acetyltransferase

The biosynthetic logic and enzymatic machinery of approved fungi-derived pharmaceuticals and agricultural biopesticides

Covering: 2000 to 2023The kingdom Fungi has become a remarkably valuable source of structurally complex natural products (NPs) with diverse bioactivities. Since the revolutionary discovery and application of the antibiotic penicillin from Penicillium, a number of fungi-derived NPs have been developed and approved into pharmaceuticals and pesticide agents using traditional "activity-guided" approaches. Although emerging genome mining algorithms and surrogate expression hosts have brought revolutionary approaches to NP discovery, the time and costs involved in developing these into new drugs can still be prohibitively high. Therefore, it is essential to maximize the utility of existing drugs by rational design and systematic production of new chemical structures based on these drugs by synthetic biology. To this purpose, there have been great advances in characterizing the diversified biosynthetic gene clusters associated with the well-known drugs and in understanding the biosynthesis logic mechanisms and enzymatic transformation processes involved in their production. We describe advances made in the heterogeneous reconstruction of complex NP scaffolds using fungal polyketide synthases (PKSs), non-ribosomal peptide synthetases (NRPSs), PKS/NRPS hybrids, terpenoids, and indole alkaloids and also discuss mechanistic insights into metabolic engineering, pathway reprogramming, and cell factory development. Moreover, we suggest pathways for expanding access to the fungal chemical repertoire by biosynthesis of representative family members via common platform intermediates and through the rational manipulation of natural biosynthetic machineries for drug discovery.

Cephalosporin resistance, tolerance, and approaches to improve their activities

Cephalosporins comprise a β-lactam antibiotic class whose first members were discovered in 1945 from the fungus Cephalosporium acremonium. Their clinical use for Gram-negative bacterial infections is widespread due to their ability to traverse outer membranes through porins to gain access to the periplasm and disrupt peptidoglycan synthesis. More recent members of the cephalosporin class are administered as last resort treatments for complicated urinary tract infections, MRSA, and other multi-drug resistant pathogens, such as Neisseria gonorrhoeae. Unfortunately, there has been a global increase in cephalosporin-resistant strains, heteroresistance to this drug class has been a topic of increasing concern, and tolerance and persistence are recognized as potential causes of cephalosporin treatment failure. In this review, we summarize the cephalosporin antibiotic class from discovery to their mechanisms of action, and discuss the causes of cephalosporin treatment failure, which include resistance, tolerance, and phenomena when those qualities are exhibited by only small subpopulations of bacterial cultures (heteroresistance and persistence). Further, we discuss how recent efforts with cephalosporin conjugates and combination treatments aim to reinvigorate this antibiotic class.

Fungal BGCs for Production of Secondary Metabolites: Main Types, Central Roles in Strain Improvement, and Regulation According to the Piano Principle

Filamentous fungi are one of the most important producers of secondary metabolites. Some of them can have a toxic effect on the human body, leading to diseases. On the other hand, they are widely used as pharmaceutically significant drugs, such as antibiotics, statins, and immunosuppressants. A single fungus species in response to various signals can produce 100 or more secondary metabolites. Such signaling is possible due to the coordinated regulation of several dozen biosynthetic gene clusters (BGCs), which are mosaically localized in different regions of fungal chromosomes. Their regulation includes several levels, from pathway-specific regulators, whose genes are localized inside BGCs, to global regulators of the cell (taking into account changes in pH, carbon consumption, etc.) and global regulators of secondary metabolism (affecting epigenetic changes driven by velvet family proteins, LaeA, etc.). In addition, various low-molecular-weight substances can have a mediating effect on such regulatory processes. This review is devoted to a critical analysis of the available data on the "turning on" and "off" of the biosynthesis of secondary metabolites in response to signals in filamentous fungi. To describe the ongoing processes, the model of "piano regulation" is proposed, whereby pressing a certain key (signal) leads to the extraction of a certain sound from the "musical instrument of the fungus cell", which is expressed in the production of a specific secondary metabolite.

Subcellular localization of fungal specialized metabolites

Fungal specialized metabolites play an important role in the environment and have impacted human health and survival significantly. These specialized metabolites are often the end product of a series of sequential and collaborating biosynthetic enzymes that reside within different subcellular compartments. A wide variety of methods have been developed to understand fungal specialized metabolite biosynthesis in terms of the chemical conversions and the biosynthetic enzymes required, however there are far fewer studies elucidating the compartmentalization of the same enzymes. This review illustrates the biosynthesis of specialized metabolites where the localization of all, or some, of the biosynthetic enzymes have been determined and describes the methods used to identify the sub-cellular localization.

Penicillium chrysogenum, a Vintage Model with a Cutting-Edge Profile in Biotechnology

The discovery of penicillin entailed a decisive breakthrough in medicine. No other medical advance has ever had the same impact in the clinical practise. The fungus Penicillium chrysogenum (reclassified as P. rubens) has been used for industrial production of penicillin ever since the forties of the past century; industrial biotechnology developed hand in hand with it, and currently P. chrysogenum is a thoroughly studied model for secondary metabolite production and regulation. In addition to its role as penicillin producer, recent synthetic biology advances have put P. chrysogenum on the path to become a cell factory for the production of metabolites with biotechnological interest. In this review, we tell the history of P. chrysogenum, from the discovery of penicillin and the first isolation of strains with high production capacity to the most recent research advances with the fungus. We will describe how classical strain improvement programs achieved the goal of increasing production and how the development of different molecular tools allowed further improvements. The discovery of the penicillin gene cluster, the origin of the penicillin genes, the regulation of penicillin production, and a compilation of other P. chrysogenum secondary metabolites will also be covered and updated in this work.

Transport systems, intracellular traffic of intermediates and secretion of β-lactam antibiotics in fungi

Fungal secondary metabolites are synthesized by complex biosynthetic pathways catalized by enzymes located in different subcellular compartments, thus requiring traffic of precursors and intermediates between them. The β-lactam antibiotics penicillin and cephalosporin C serve as an excellent model to understand the molecular mechanisms that control the subcellular localization of secondary metabolites biosynthetic enzymes. Optimal functioning of the β-lactam biosynthetic enzymes relies on a sophisticated temporal and spatial organization of the enzymes, the intermediates and the final products. The first and second enzymes of the penicillin pathway, ACV synthetase and IPN synthase, in Penicillium chrysogenum and Aspergillus nidulans are cytosolic. In contrast, the last two enzymes of the penicillin pathway, phenylacetyl-CoA ligase and isopenicillin N acyltransferase, are located in peroxisomes working as a tandem at their optimal pH that coincides with the peroxisomes pH. Two MFS transporters, PenM and PaaT have been found to be involved in the import of the intermediates isopenicillin N and phenylacetic acid, respectively, into peroxisomes. Similar compartmentalization of intermediates occurs in Acremonium chrysogenum; two enzymes isopenicillin N-CoA ligase and isopenicillin N-CoA epimerase, that catalyse the conversion of isopenicillin N in penicillin N, are located in peroxisomes. Two genes encoding MFS transporters, cefP and cefM, are located in the early cephalosporin gene cluster. These transporters have been localized in peroxisomes by confocal fluorescence microscopy. A third gene of A. chrysogenum, cefT, encodes an MFS protein, located in the cell membrane involved in the secretion of cephalosporin C, although cefT-disrupted mutants are still able to export cephalosporin by redundant transporters. The secretion of penicillin from peroxisomes to the extracellular medium is still unclear. Attempts have been made to identify a gene encoding the penicillin secretion protein among the 48 ABC-transporters of P. chrysogenum. The highly efficient secretion system that exports penicillin against a concentration gradient may involve active penicillin extrusion systems mediated by vesicles that fuse to the cell membrane. However, there is no correlation of pexophagy with penicillin or cephalosporin formation since inactivation of pexophagy leads to increased penicillin or cephalosporin biosynthesis due to preservation of peroxisomes. The penicillin biosynthesis finding shows that in order to increase biosynthesis of novel secondary metabolites it is essential to adequately target enzymes to organelles.

Biosynthetic Study of Cephalosporin P1 Reveals a Multifunctional P450 Enzyme and a Site-Selective Acetyltransferase

Fusidane-type antibiotics are a group of triterpenoid antibiotics. They include helvolic acid, fusidic acid, and cephalosporin P₁, among which fusidic acid has been used clinically. We have recently elucidated the biosynthesis of helvolic acid and fusidic acid, which share an early biosynthetic route involving six conserved enzymes. Here, we report two separate gene clusters for cephalosporin P₁ biosynthesis. One consists of the six conserved genes, and the other contains three genes encoding a P450 enzyme (CepB4), an acetyltransferase (CepD2), and a short-chain dehydrogenase/reductase (CepC2). Introduction of these three genes into Aspergillus oryzae, which harbors the six conserved genes, produced cephalosporin P₁. Stepwise introduction revealed that CepB4 not only catalyzes stereoselective dual oxidation of C6 and C7, but also monooxygenation of C6 or C7. This led to the generation of five new analogues. Using monohydroxylated products as substrates, we demonstrated that CepD2 specifically acetylates C6-OH, although both C6-OH and C7-OH acetylated analogues have been identified in nature.

Metabolic Gene Clusters in Eukaryotes

In bacteria, more than half of the genes in the genome are organized in operons. In contrast, in eukaryotes, functionally related genes are usually dispersed across the genome. There are, however, numerous examples of functional clusters of nonhomologous genes for metabolic pathways in fungi and plants. Despite superficial similarities with operons (physical clustering, coordinate regulation), these clusters have not usually originated by horizontal gene transfer from bacteria, and (unlike operons) the genes are typically transcribed separately rather than as a single polycistronic message. This clustering phenomenon raises intriguing questions about the origins of clustered metabolic pathways in eukaryotes and the significance of clustering for pathway function. Here we review metabolic gene clusters from fungi and plants, highlight commonalities and differences, and consider how these clusters form and are regulated. We also identify opportunities for future research in the areas of large-scale genomics, synthetic biology, and experimental evolution.

Study on genetic engineering of Acremonium chrysogenum, the cephalosporin C producer

Acremonium chrysogenum is an important filamentous fungus which produces cephalosporin C in industry. This review summarized the study on genetic engineering of Acremonium chrysogenum, including biosynthesis and regulation for fermentation of cephalosporin C, molecular techniques, molecular breeding and transcriptomics of Acremonium chrysogenum. We believe with all the techniques available and full genomic sequence, the industrial strain of Acremonium chrysogenum can be genetically modified to better serve the pharmaceutical industry.

Genome mining reveals the presence of a conserved gene cluster for the biosynthesis of ergot alkaloid precursors in the fungal family Arthrodermataceae

Genome sequence analysis of different fungi of the family Arthrodermataceae revealed the presence of a gene cluster consisting of five genes with high sequence similarity to those involved in the early common steps of ergot alkaloid biosynthesis in Aspergillus fumigatus and Claviceps purpurea. To provide evidence that this cluster is involved in ergot alkaloid biosynthesis, the gene ARB_04646 of the fungus Arthroderma benhamiae was cloned into pQE60 and expressed in Escherichia coli. Enzyme assays with the soluble tetrameric His(6)-tagged protein proved unequivocally that the deduced gene product, here termed ChaDH, catalysed the oxidation of chanoclavine-I in the presence of NAD(+), resulting in the formation of chanoclavine-I aldehyde. The enzyme product was unequivocally proven by NMR and MS analyses. Therefore, ChaDH functions as a chanoclavine-I dehydrogenase. K(m) values for chanoclavine-I and NAD(+) were 0.09 and 0.36 mM, respectively. Turnover number was 0.76 s(-1).

Expression of cefF significantly decreased deacetoxycephalosporin C formation during cephalosporin C production in Acremonium chrysogenum

Deacetoxycephalosporin C (DAOC) is not only the precursor but also one of the by-products during cephalosporin C (CPC) biosynthesis. One enzyme (DAOC/DAC synthase) is responsible for the two-step conversion of penicillin N into deacetylcephalosporin C (DAC) in Acremonium chrysogenum, while two enzymes (DAOC synthase and DAOC hydroxylase) were involved in this reaction in Streptomyces clavuligerus and Amycolatopsis lactamdurans (Nocardia lactamdurans). In this study, the DAOC hydroxylase gene cefF was cloned from Streptomyces clavuligerus and introduced into Acremonium chrysogenum through Agrobacterium tumefaciens-mediated transformation. When cefF was expressed under the promoter of pcbC, the ratio of DAOC/CPC in the fermentation broth significantly decreased. These results suggested that introduction of cefF could function quite well in Acremonium chrysogenum and successfully reduce the content of DAOC in the CPC fermentation broth. This work offered a practical way to improve the CPC purification and reduce its production cost.

Role of peroxisomes in the biosynthesis and secretion of β-lactams and other secondary metabolites

Peroxisomes are eukaryotic organelles surrounded by a single bilayer membrane, containing a variety of proteins depending on the organism; they mainly perform degradation reactions of toxic metabolites (detoxification), catabolism of linear and branched-chain fatty acids, and removal of H(2)O(2) (formed in some oxidative processes) by catalase. Proteins named peroxins are involved in recruiting, transporting, and introducing the peroxisomal matrix proteins into the peroxisomes. The matrix proteins contain the peroxisomal targeting signals PTS1 and/or PTS2 that are recognized by the peroxins Pex5 and Pex7, respectively. Initial evidence indicated that the penicillin biosynthetic enzyme isopenicillin N acyltransferase (IAT) of Penicillium chrysogenum is located inside peroxisomes. There is now solid evidence (based on electron microscopy and/or biochemical data) confirming that IAT and the phenylacetic acid- and fatty acid-activating enzymes are also located in peroxisomes. Similarly, the Acremonium chrysogenum CefD1 and CefD2 proteins that perform the central reactions (activation and epimerization of isopenicillin N) of the cephalosporin pathway are targeted to peroxisomes. Growing evidence supports the conclusion that some enzymes involved in the biosynthesis of mycotoxins (e.g., AK-toxin), and the biosynthesis of signaling molecules in plants (e.g., jasmonic acid or auxins) occur in peroxisomes. The high concentration of substrates (in many cases toxic to the cytoplasm) and enzymes inside the peroxisomes allows efficient synthesis of metabolites with interesting biological or pharmacological activities. This compartmentalization poses additional challenges to the cell due to the need to import the substrates into the peroxisomes and to export the final products; the transporters involved in these processes are still very poorly known. This article focuses on new aspects of the metabolic processes occurring in peroxisomes, namely the degradation and detoxification processes that lead to the biosynthesis and secretion of secondary metabolites.

Characterization of a novel peroxisome membrane protein essential for conversion of isopenicillin N into cephalosporin C

The mechanisms of compartmentalization of intermediates and secretion of penicillins and cephalosporins in β-lactam antibiotic-producing fungi are of great interest. In Acremonium chrysogenum, there is a compartmentalization of the central steps of the CPC (cephalosporin C) biosynthetic pathway. In the present study, we found in the 'early' CPC cluster a new gene named cefP encoding a putative transmembrane protein containing 11 transmembrane spanner. Targeted inactivation of cefP by gene replacement showed that it is essential for CPC biosynthesis. The disrupted mutant is unable to synthesize cephalosporins and secretes a significant amount of IPN (isopenicillin N), indicating that the mutant is blocked in the conversion of IPN into PenN (penicillin N). The production of cephalosporin in the disrupted mutant was restored by transformation with both cefP and cefR (a regulatory gene located upstream of cefP), but not with cefP alone. Fluorescence microscopy studies with an EGFP (enhanced green fluorescent protein)-SKL (Ser-Lys-Leu) protein (a peroxisomal-targeted marker) as a control showed that the red-fluorescence-labelled CefP protein co-localized in the peroxisomes with the control peroxisomal protein. In summary, CefP is a peroxisomal membrane protein probably involved in the import of IPN into the peroxisomes where it is converted into PenN by the two-component CefD1/CefD2 protein system.

Recombinant microorganisms for industrial production of antibiotics

The enhancement of industrial antibiotic yield has been achieved through technological innovations and traditional strain improvement programs based on random mutation and screening. The development of recombinant DNA techniques and their application to antibiotic producing microorganisms has allowed yield increments and the design of biosynthetic pathways giving rise to new antibiotics. Genetic manipulations of the cephalosporin producing fungus Cephalosporium acremonium have included yield improvements, accomplished increasing biosynthetic gene dosage or enhancing oxygen uptake, and new biosynthetic capacities as 7-aminocephalosporanic acid (7-ACA) or penicillin G production. Similarly, in Penicillium chrysogenum, the industrial penicillin producing fungus, heterologous expression of cephalosporin biosynthetic genes has led to the biosynthesis of adipyl-7-aminodeacetoxycephalosporanic acid (adipyl-7-ADCA) and adipyl-7-ACA, compounds that can be transformed into the economically relevant 7-ADCA and 7-ACA intermediates. Escherichia coli expression of the genes encoding D-amino acid oxidase and cephalosporin acylase activities has simplified the bioconversion of cephalosporin C into 7-ACA, eliminating the use of organic solvents. The genetic manipulation of antibiotic producing actinomycetes has allowed productivity increments and the development of new hybrid antibiotics. A legal framework has been developed for the confined manipulation of genetically modified organisms.

Regulation and compartmentalization of β-lactam biosynthesis

Penicillins and cephalosporins are β‐lactam antibiotics widely used in human medicine. The biosynthesis of these compounds starts by the condensation of the amino acids l‐α‐aminoadipic acid, l‐cysteine and l‐valine to form the tripeptide δ‐l‐α‐aminoadipyl‐l‐cysteinyl‐d‐valine catalysed by the non‐ribosomal peptide ‘ACV synthetase’. Subsequently, this tripeptide is cyclized to isopenicillin N that in Penicillium is converted to hydrophobic penicillins, e.g. benzylpenicillin. In Acremonium and in streptomycetes, isopenicillin N is later isomerized to penicillin N and finally converted to cephalosporin. Expression of genes of the penicillin (pcbAB, pcbC, pendDE) and cephalosporin clusters (pcbAB, pcbC, cefD1, cefD2, cefEF, cefG) is controlled by pleitropic regulators including LaeA, a methylase involved in heterochromatin rearrangement. The enzymes catalysing the last two steps of penicillin biosynthesis (phenylacetyl‐CoA ligase and isopenicillin N acyltransferase) are located in microbodies, as shown by immunoelectron microscopy and microbodies proteome analyses. Similarly, the Acremonium two‐component CefD1–CefD2 epimerization system is also located in microbodies. This compartmentalization implies intracellular transport of isopenicillin N (in the penicillin pathway) or isopenicillin N and penicillin N in the cephalosporin route. Two transporters of the MFS family cefT and cefM are involved in transport of intermediates and/or secretion of cephalosporins. However, there is no known transporter of benzylpenicillin despite its large production in industrial strains.

The transporter CefM involved in translocation of biosynthetic intermediates is essential for cephalosporin production

The cluster of early cephalosporin biosynthesis genes (pcbAB, pcbC, cefD1, cefD2 and cefT of Acremonium chrysogenum) contains all of the genes required for the biosynthesis of the cephalosporin biosynthetic pathway intermediate penicillin N. Downstream of the cefD1 gene, there is an unassigned open reading frame named cefM encoding a protein of the MFS (major facilitator superfamily) with 12 transmembrane domains, different from the previously reported cefT. Targeted inactivation of cefM by gene replacement showed that it is essential for cephalosporin biosynthesis. The disrupted mutant accumulates a significant amount of penicillin N, is unable to synthesize deacetoxy-, deacetyl-cephalosporin C and cephalosporin C and shows impaired differentiation into arthrospores. Complementation of the disrupted mutant with the cefM gene restored the intracellular penicillin N concentration to normal levels and allowed synthesis and secretion of the cephalosporin intermediates and cephalosporin C. A fused cefM-gfp gene complemented the cefM-disrupted mutant, and the CefM–GFP (green fluorescent protein) fusion was targeted to intracellular microbodies that were abundant after 72 h of culture in the differentiating hyphae and in the arthrospore chains, coinciding with the phase of intense cephalosporin biosynthesis. Since the dual-component enzyme system CefD1–CefD2 that converts isopenicillin N into penicillin N contains peroxisomal targeting sequences, it is probable that the epimerization step takes place in the peroxisome matrix. The CefM protein seems to be involved in the translocation of penicillin N from the peroxisome (or peroxisome-like microbodies) lumen to the cytosol, where it is converted into cephalosporin C.

RNA-silencing in Penicillium chrysogenum and Acremonium chrysogenum: validation studies using beta-lactam genes expression

In this work we report the development and validation of a new RNA interference vector (pJL43-RNAi) containing a double-stranded RNA expression cassette for gene silencing in the filamentous fungi Penicillium chrysogenum and Acremonium chrysogenum. Classical targeted gene disruption in these fungi is very laborious and inefficient due to the low frequency of homologous recombination. The RNAi vector has been validated by testing the attenuation of two different genes of the beta-lactam pathway; pcbC in P. chrysogenum and cefEF in A. chrysogenum. Quantification of mRNA transcript levels and antibiotic production showed knockdown of pcbC and cefEF genes in randomly isolated transformants of P. chrysogenum and A. chrysogenum, respectively. The process is efficient; 15 to 20% of the selected transformants were found to be knockdown mutants showing reduced penicillin or cephalosporin production. This new RNAi vector opens the way for exploring gene function in the genomes of P. chrysogenum and A. chrysogenum.

Deacetylcephalosporin C production in Penicillium chrysogenum by expression of the isopenicillin N epimerization, ring expansion, and acetylation genes

Penicillium chrysogenum npe6 lacking isopenicillin N acyltransferase activity is an excellent host for production of different beta-lactam antibiotics. We have constructed P. chrysogenum strains expressing cefD1, cefD2, cefEF, and cefG genes cloned from Acremonium chrysogenum. Northern analysis revealed that the four genes were expressed in P. chrysogenum. The recombinant strains TA64, TA71, and TA98 secreted significant amounts of deacetylcephalosporin C, but cephalosporin C was not detected in the culture broths. DAC-acetyltransferase activity was found in all transformants containing the cefG gene. HPLC analysis of cell extracts showed that transformant TA64, TA71, and TA98 accumulate intracellularly deacetylcephalosporin C and, in the last strain (TA98), also cephalosporin C. Mass spectra analysis confirmed that transformant TA98 synthesize true deacetylcephalosporin C and cephalosporin C. Even when accumulated intracellularly, cephalosporin C was not found in the culture broth.

5S clavam biosynthetic genes are located in both the clavam and paralog gene clusters in Streptomyces clavuligerus

The Streptomyces clavuligerus clavam gene cluster was examined to identify genes specifically involved in 5S clavam biosynthesis. A reduction/loss of 5S clavam production was seen in cvm2 and cvm5 gene mutants, and a clavam metabolite not previously observed, 2-carboxymethylideneclavam, accumulated in the cvm5 mutant. Disruption of additional genes from the region of the clavam cluster did not have any effect on 5S clavam production. Examination of the paralog gene cluster region for 5S clavam biosynthetic genes led to the identification of cvm6P and cvm7P, which encode a putative aminotransferase and a transcriptional regulator, respectively. Mutants defective in cvm6P and cvm7P were completely blocked in 5S clavam but not clavulanic acid production. The loss of 5S clavam production in cvm7P mutants suggests that this gene encodes a transcriptional regulator specific for 5S clavam metabolite biosynthesis.

Transcriptional and bioinformatic analysis of the 56.8kb DNA region amplified in tandem repeats containing the penicillin gene cluster in Penicillium chrysogenum

High penicillin-producing strains of Penicillium chrysogenum contain 6-14 copies of the three clustered structural biosynthetic genes, pcbAB, pcbC, and penDE [Barredo, J.L., Díez, B., Alvarez, E., Martín, J.F., 1989. Large amplification of a 35-kb DNA fragment carrying two penicillin biosynthetic genes in high penicillin producing strains of Penicillium chrysogenum. Curr. Genet. 16, 453-459; Smith, D.J., Bull, J.H., Edwards, J., Turner, G., 1989. Amplification of the isopenicillin N synthetase gene in a strain of Penicillium chrysogenum producing high levels of penicillin. Mol. Gen. Genet. 216, 492-497.] . The cluster is located in a 56.8 kb DNA region bounded by a conserved TGTAAA/T hexanucleotide that undergoes amplification in tandem repeats [Fierro, F., Barredo, J.L., Díez, B., Gutiérrez, S., Fernández, F.J., Martín, J.F., 1995. The penicillin gene cluster is amplified in tandem repeats linked by conserved hexanucleotide sequences. Proc. Natl. Acad. Sci. USA 92, 6200-6204; Newbert, R.W., Barton, B., Greaves, P., Harper, J., Turner, G., 1997. Analysis of a commercially improved Penicillium chrysogenum strain series: involvement of recombinogenic regions in amplification and deletion of the penicillin biosynthesis gene cluster. J. Ind. Microbiol. Biotechnol. 19, 18-27]. Transcriptional analysis of this amplified region (AR) revealed the presence of at least eight transcripts expressed in penicillin producing conditions. Three of them correspond to the known penicillin biosynthetic genes, pcbAB, pcbC, and penDE. To locate genes related to penicillin precursor formation, or penicillin transport and regulation we have sequenced and analyzed the 56.8 kb amplified region of P. chrysogenum AS-P-78, finding a total of 16 open reading frames. Two of these ORFs have orthologues of known function in the databases. Other ORFs showed similarities to specific domains occurring in different proteins and superfamilies which allowed to infer their probable function. ORF11 encodes a D-amino acid oxidase that might be responsible for the conversion of D-amino acids in the tripeptide L-alpha-aminoadipyl-L-cysteinyl-D-valine or other beta-lactam intermediates to deaminated by-products. ORF12 encodes a predicted protein with similarity to saccharopine dehydrogenases that seems to be related to biosynthesis of the penicillin precursor alpha-aminoadipic acid. A deletion mutant, P. chrysogenum npe10 lacking the entire AR including ORF12, shows a partial requirement of L-lysine for growth. ORF13 encodes a putative protein containing a Zn(II)2-Cys6 fungal-type DNA-binding domain, probably a transcriptional regulator. Although some of the ORFs in the AR may play roles in increasing penicillin production, none of the 13 ORFs other than pcbAB, pcbC, and penDE seem to be strictly indispensable for penicillin biosynthesis. The genes located in the P. chrysogenum AR have been compared with those found in the Aspergillus nidulans 50 kb DNA region adjacent to the penicillin gene cluster, showing no conservation between these two fungi.

Genetic improvement of processes yielding microbial products

Although microorganisms are extremely good in presenting us with an amazing array of valuable products, they usually produce them only in amounts that they need for their own benefit; thus, they tend not to overproduce their metabolites. In strain improvement programs, a strain producing a high titer is usually the desired goal. Genetics has had a long history of contributing to the production of microbial products. The tremendous increases in fermentation productivity and the resulting decreases in costs have come about mainly by mutagenesis and screening/selection for higher producing microbial strains and the application of recombinant DNA technology.

Genome-wide analysis of differentially expressed genes from Penicillium chrysogenum grown with a repressing or a non-repressing carbon source

Penicillium chrysogenum is an economically important ascomycete used as industrial producer of penicillin. However, with the exception of penicillin biosynthesis genes, little attention has been paid to the genetics of other aspects of the metabolism of this fungus. In this article we describe the first attempt of systematic analysis of expressed genes in P. chrysogenum, using a suppression subtractive hybridization approach to clone and identify sequences of genes differentially expressed in media with glucose or lactose as carbon source (penicillin-repressing or non-repressing conditions). A total of 167 clones were analysed, 95 from the glucose condition and 72 from the lactose condition. Genes differentially expressed in the glucose condition encode mainly proteins involved in the mitochondrial electron transport chain and primary metabolism. Genes expressed differentially in lactose-containing medium include genes for secondary metabolism (pcbC, isopenicillin N synthase), different hydrolases and a gene encoding a putative hexose transporter or sensor. The results provided information on how the metabolism of this fungus adapts to different carbon sources. The expression patterns of some of the genes support the hypothesis that glucose induces higher rates of respiration in P. chrysogenum while repressing secondary metabolism.

Fungal secondary metabolism — from biochemistry to genomics

Much of natural product chemistry concerns a group of compounds known as secondary metabolites. These low-molecular-weight metabolites often have potent physiological activities. Digitalis, morphine and quinine are plant secondary metabolites, whereas penicillin, cephalosporin, ergotrate and the statins are equally well known fungal secondary metabolites. Although chemically diverse, all secondary metabolites are produced by a few common biosynthetic pathways, often in conjunction with morphological development. Recent advances in molecular biology, bioinformatics and comparative genomics have revealed that the genes encoding specific fungal secondary metabolites are clustered and often located near telomeres. In this review, we address some important questions, including which evolutionary pressures led to gene clustering, why closely related species produce different profiles of secondary metabolites, and whether fungal genomics will accelerate the discovery of new pharmacologically active natural products.

Regulation of secondary metabolism in filamentous fungi

Fungal secondary metabolites are of intense interest to humankind due to their pharmaceutical (antibiotics) and/or toxic (mycotoxins) properties. In the past decade, tremendous progress has been made in understanding the genes that are associated with production of various fungal secondary metabolites. Moreover, the regulatory mechanisms controlling biosynthesis of diverse groups of secondary metabolites have been unveiled. In this review, we present the current understanding of the genetic regulation of secondary metabolism from clustering of biosynthetic genes to global regulators balancing growth, sporulation, and secondary metabolite production in selected fungi with emphasis on regulation of metabolites of agricultural concern. Particularly, the roles of G protein signaling components and developmental regulators in the mycotoxin sterigmatocystin biosynthesis in the model fungus Aspergillus nidulans are discussed in depth.

Expression of cefD2 and the conversion of isopenicillin N into penicillin N by the two-component epimerase system are rate-limiting steps in cephalosporin biosynthesis

The conversion of isopenicillin N into penicillin N in Acremonium chrysogenum is catalyzed by an epimerization system that involves an isopenicillin N-CoA synthethase and isopenicillin N-CoA epimerase, encoded by the genes cefD1 and cefD2. Several transformants containing two to seven additional copies of both genes were obtained. Four of these transformants (TMCD26, TMCD53, TMCD242 and TMCD474) showed two-fold higher IPN epimerase activity than the untransformed A. chrysogenum C10, and produced 80 to 100% more cephalosporin C and deacetylcephalosporin C than the parental strain. A second class of transformants, including TMCD2, TMCD32 and TMCD39, in contrast, showed a drastic reduction in cephalosporin biosynthesis relative to the untransformed control. These transformants had no detectable IPN epimerase activity and did not produce cephalosporin C or deacetylcephalosporin C. They also expressed both endogenous and exogenous cefD2 genes only after long periods (72-96 h) of incubation, as shown by Northern analysis, and were impaired in mycelial branching in liquid cultures. The negative effect of amplification of the cefD1 - cefD2 gene cluster in this second class of transformants is not correlated with high gene dosage, but appears to be due to exogenous DNA integration into a specific locus, which results in a pleiotropic effect on growth and cefD2 expression.

Metabolic engineering of beta-lactam production

Metabolic engineering has become a rational alternative to classical strain improvement in optimisation of beta-lactam production. In metabolic engineering directed genetic modification are introduced to improve the cellular properties of the production strains. This has resulted in substantial increases in the existing beta-lactam production processes. Furthermore, pathway extension, by heterologous expression of novel genes in well-characterised strains, has led to introduction of new fermentation processes that replace environmentally damaging chemical methods. This minireview discusses the recent developments in metabolic engineering and the applications of this approach for improving beta-lactam production.

Unraveling the methionine-cephalosporin puzzle in Acremonium chrysogenum

Methionine has long been known as the major stimulant of the formation of cephalosporin C in Acremonium chrysogenum. Enzymatic and genetic studies of methionine have revealed that it induces four of the enzymes of cephalosporin-C biosynthesis at the level of transcription. It is also converted to cysteine, one of three precursors of cephalosporin C, by cystathionine-gamma-lyase. The main effect of methionine on cephalosporin production results from its regulatory role, which can be duplicated by the non-sulfur analog norleucine. Eliminating cystathionine-gamma-lyase prevents the enhancing precursor effect of methionine on cephalosporin-C production, and cystathionine-gamma-lyase overproduction in moderate doses increases cephalosporin-C formation.

A novel epimerization system in fungal secondary metabolism involved in the conversion of isopenicillin N into penicillin N in Acremonium chrysogenum

The epimerization step that converts isopenicillin N into penicillin N during cephalosporin biosynthesis has remained uncharacterized despite its industrial relevance. A transcriptional analysis of a 9-kb region located downstream of the pcbC gene revealed the presence of two transcripts that correspond to the genes named cefD1 and cefD2 encoding proteins with high similarity to long chain acyl-CoA synthetases and acyl-CoA racemases from Mus musculus, Homo sapiens, and Rattus norvegicus. Both genes are expressed in opposite orientations from a bidirectional promoter region. Targeted inactivation of cefD1 and cefD2 was achieved by the two-marker gene replacement procedure. Disrupted strains lacked isopenicillin N epimerase activity, were blocked in cephalosporin C production, and accumulated isopenicillin N. Complementation in trans of the disrupted nonproducer mutant with both genes restored epimerase activity and cephalosporin biosynthesis. However, when cefD1 or cefD2 were introduced separately into the double-disrupted mutant, no epimerase activity was detected, indicating that the concerted action of both proteins encoded by cefD1 and cefD2 is required for epimerization of isopenicillin N into penicillin N. This epimerization system occurs in eukaryotic cells and is entirely different from the known epimerization systems involved in the biosynthesis of bacterial beta-lactam antibiotics.

Environmentally safe production of 7-aminodeacetoxycephalosporanic acid (7-ADCA) using recombinant strains of Acremonium chrysogenum

Medically useful semisynthetic cephalosporins are made from 7-aminodeacetoxycephalosporanic acid (7-ADCA) or 7-aminocephalosporanic acid (7-ACA). Here we describe a new industrially amenable bioprocess for the production of the important intermediate 7-ADCA that can replace the expensive and environmentally unfriendly chemical method classically used. The method is based on the disruption and one-step replacement of the cefEF gene, encoding the bifunctional expandase/hydroxylase activity, of an actual industrial cephalosporin C production strain of Acremonium chrysogenum. Subsequent cloning and expression of the cefE gene from Streptomyces clavuligerus in A. chrysogenum yield recombinant strains producing high titers of deacetoxycephalosporin C (DAOC). Production level of DAOC is nearly equivalent (75-80%) to the total beta-lactams biosynthesized by the parental overproducing strain. DAOC deacylation is carried out by two final enzymatic bioconversions catalyzed by D-amino acid oxidase (DAO) and glutaryl acylase (GLA) yielding 7-ADCA. In contrast to the data reported for recombinant strains of Penicillium chrysogenum expressing ring expansion activity, no detectable contamination with other cephalosporin intermediates occurred.

Molecular characterization of the Acremonium chrysogenum cefG gene product: the native deacetylcephalosporin C acetyltransferase is not processed into subunits

Constructions starting at each of the three in-frame ATG codons of the Acremonium chrysogenum cefG gene (Met1, Met46 and Met60) were expressed in Escherichia coli, obtaining proteins of 49, 44 and 43 kDa, respectively. All three proteins showed deacetylcephalosporin C (DAC) acetyltransferase activity. The native A. chrysogenum DAC acetyltransferase was purified to electrophoretic homogeneity by immunoaffinity chromatography. It showed a molecular mass of 50 kDa by filtration in calibrated Sephadex G-75 SF or Superose 12 (FPLC) columns. The N-terminal end of the pure DAC acetyltransferase was Met-Leu-Pro-Ser-Ala-Gln-Val-Ala-Arg-Leu, which matched perfectly the deduced amino acid sequence starting at Met1. The putative alpha- and beta-subunits of DAC acetyltransferase were also obtained in E. coli but showed no enzymic activity either separately or in combination. Immunoblotting (Western) analysis revealed that the 50 kDa DAC acetyltransferase showed high protein levels in A. chrysogenum cultures at 72 and 96 h and decreased sharply thereafter, but in all cases no detectable processing of the enzyme into subunits was found. Three different A. chrysogenum strains (including the wild-type Brotzu strain and two high-cephalosporin-producing mutants) showed the same unprocessed 50 kDa DAC acetyltransferase. The non-producer mutant ATCC 20371 showed no DAC acetyltransferase protein band but formed a normal transcript of 1.4 kb.

Molecular characterization and sequence of a methionine biosynthetic locus from Pseudomonas syringae

Two methionine biosynthetic genes in Pseudomonas syringae pv. syringae, metX and metW, were isolated, sequenced, and evaluated for their roles in methionine biosynthesis and bacterial fitness on leaf surfaces. The metXW locus was isolated on a 1.8-kb DNA fragment that was required for both methionine prototrophy and wild-type epiphytic fitness. Sequence analysis identified two consecutive open reading frames (ORFs), and in vitro transcription-translation experiments provided strong evidence that the ORFs encode proteins with the predicted molecular masses of 39 and 22.5 kDa. The predicted amino acid sequence of MetX (39 kDa) showed homology to several known and putative homoserine O-acetyltransferases. This enzyme is the first enzyme in the methionine biosynthetic pathway of fungi, gram-negative bacteria of the genus Leptospira, and several gram-positive bacterial genera. Both metX and metW were required for methionine biosynthesis, and transcription from both genes was not repressed by methionine. MetW (22.5 kDa) did not show significant homology to any known protein, including prokaryotic and eukaryotic methionine biosynthetic enzymes. Several classes of methionine auxotrophs, including metX and metW mutants, exhibit reduced fitness on leaf surfaces, indicating a requirement for methionine prototrophy in wild-type epiphytic fitness. This requirement is enhanced under environmentally stressful conditions, suggesting a role for methionine prototrophy in bacterial stress tolerance.

Molecular regulation of beta-lactam biosynthesis in filamentous fungi

The most commonly used beta-lactam antibiotics for the therapy of infectious diseases are penicillin and cephalosporin. Penicillin is produced as an end product by some fungi, most notably by Aspergillus (Emericella) nidulans and Penicillium chrysogenum. Cephalosporins are synthesized by both bacteria and fungi, e.g., by the fungus Acremonium chrysogenum (Cephalosporium acremonium). The biosynthetic pathways leading to both secondary metabolites start from the same three amino acid precursors and have the first two enzymatic reactions in common. Penicillin biosynthesis is catalyzed by three enzymes encoded by acvA (pcbAB), ipnA (pcbC), and aatA (penDE). The genes are organized into a cluster. In A. chrysogenum, in addition to acvA and ipnA, a second cluster contains the genes encoding enzymes that catalyze the reactions of the later steps of the cephalosporin pathway (cefEF and cefG). Within the last few years, several studies have indicated that the fungal beta-lactam biosynthesis genes are controlled by a complex regulatory network, e. g., by the ambient pH, carbon source, and amino acids. A comparison with the regulatory mechanisms (regulatory proteins and DNA elements) involved in the regulation of genes of primary metabolism in lower eukaryotes is thus of great interest. This has already led to the elucidation of new regulatory mechanisms. Furthermore, such investigations have contributed to the elucidation of signals leading to the production of beta-lactams and their physiological meaning for the producing fungi, and they can be expected to have a major impact on rational strain improvement programs. The knowledge of biosynthesis genes has already been used to produce new compounds.

Autonomously replicating plasmids carrying the AMA1 region in Penicillium chrysogenum

Plasmid vectors containing the AMA1 sequence transformed with high efficiency and replicated autonomously in Penicillium chrysogenum. The efficiency of transformation of P. chrysogenum was related to the length of the AMA1 fragment used for constructing the different autonomously replicating plasmids. One of the two palindromic inverted repeats of AMA1 (the 2.2-kb SalI-HindIII fragment) is sufficient to confer autonomous replication and a high transformation efficiency. Deletion of the 0.6-kb central fragment located between the inverted repeats did not affect either the ability of the plasmids to replicate autonomously or the efficiency of transformation, but did alter the mitotic stability and the plasmid copy number. Deletion of any fragment of the 2.2-kb repeat caused the loss of the ability to replicate autonomously and reduced the transformation efficiency. Most of the transformants retained the original plasmid configuration, as multimers and without reorganization, after several rounds of autonomous replication. The AMA1 region works as an origin of replication in P. chrysogenum and A. nidulans but not apparently in Acremonium chrysogenum.

The penicillin gene cluster is amplified in tandem repeats linked by conserved hexanucleotide sequences

The penicillin biosynthetic genes (pcbAB, pcbC, penDE) of Penicillium chrysogenum AS-P-78 were located in a 106.5-kb DNA region that is amplified in tandem repeats (five or six copies) linked by conserved TTTACA sequences. The wild-type strains P. chrysogenum NRRL 1951 and Penicillium notatum ATCC 9478 (Fleming's isolate) contain a single copy of the 106.5-kb region. This region was bordered by the same TTTACA hexanucleotide found between tandem repeats in strain AS-P-78. A penicillin overproducer strain, P. chrysogenum E1, contains a large number of copies in tandem of a 57.9-kb DNA fragment, linked by the same hexanucleotide or its reverse complementary TGTAAA sequence. The deletion mutant P. chrysogenum npe10 showed a deletion of 57.9 kb that corresponds exactly to the DNA fragment that is amplified in E1. The conserved hexanucleotide sequence was reconstituted at the deletion site. The amplification has occurred within a single chromosome (chromosome I). The tandem reiteration and deletion appear to arise by mutation-induced site-specific recombination at the conserved hexanucleotide sequences.

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.

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.

Molecular characterization of three loss-of-function mutations in the isopenicillin N-acyltransferase gene (penDE) of Penicillium chrysogenum

Five mutants of Penicillium chrysogenum blocked in penicillin biosynthesis (npe) which are deficient in isopenicillin N-acyltransferase were isolated previously. Three of these mutants, npe6, npe7, and npe8, have been characterized at the molecular level and compared with npe10, a deletion mutant. Transcripts of normal size (1.15 kb) of the penDE genes, which encode isopenicillin N-acyltransferase, and also of the pcbAB (11.5 kb) and pcbC (1.1 kb) genes were observed in all mutants except for the npe10 mutant. Immunoblotting studies using antibodies against isopenicillin N-acyltransferase showed that all mutants (except npe10) formed the 40-kDa (unprocessed) protein and the 29-kDa subunit of the isopenicillin N-acyltransferase. The 11-kDa subunit could not be observed in the immunoblots. The mutant penDE genes of strains npe6, npe7, and npe8 were cloned and sequenced. These three strains showed a mutation in the penDE genes which results in a single amino acid change in each modified isopenicillin N-acyltransferase. The mutation in npe6 resulted in a change of Gly-150 to Val, whereas the mutation in both npe7 and npe8 introduced a change of Glu-258 to Lys. Replacement of the Val-150 and Lys-258 mutations by constructing hybrid isopenicillin N-acyltransferase molecules led to the recovery of the isopenicillin N-acyltransferase activity. The mutations in npe6, npe7, and npe8 do not affect the ability of the 40-kDa isopenicillin N-acyltransferase to be processed into the component subunits.

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.