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.

The gene encoding gamma-actin from the cephalosporin producer Acremonium chrysogenum

The nucleotide sequence of a 3240-bp genomic fragment including the gamma-actin-encoding gene from Acremonium chrysogenum has been determined, showing an open reading frame of 1691 bp, interrupted by five introns with fungal consensus splice-site junctions. The untranslated regions of the actA gene contain a consensus TATA box, a CCAAT motif, pyrimidine stretches and the polyadenylation sequence AATAA. The predicted protein (375 amino acids) revealed high identity to gamma-actins from fungi (> 90%). Gene phylogenies constructed using DNA and protein sequences support the grouping of A. chrysogenum actin close to those from the majority of the filamentous fungi. The actA gene is present as a single copy in the genome of A. chrysogenum; and its expression level, opposite to pcbC and cefEF cephalosporin biosynthetic genes, was steady during cephalosporin fermentation, showing a single 1.4-kb transcript.

Production of cephalosporin C by immobilized cells of Cephalosporium acremonium

Cephalosporium acremonium ATCC 48272 cells were immobilized on various adsorbents and in various entrapment matrices. The influence of the incubation period, the best immobilization technique and the optimum concentrations of the selected matrices were investigated. From the results of the repeated batch fermentation in shake flasks, a good level of antibiotic was maintained for a period of about 19 days using 4% calcium alginate and 1% glass wool as entrapment and adsorbent supports, respectively.

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.

Glucose dependent transcriptional expression of the cre1 gene in Acremonium chrysogenum strains showing different levels of cephalosporin C production

The cre1 gene from the beta-lactam producer Acremonium chrysogenum has been isolated and characterized in order to study glucose-dependent gene expression in this biotechnically important fungus. The deduced protein sequence is highly similar to amino-acid sequences of other known glucose repressors from filamentous fungi, and carries conserved zinc-finger and regulatory motifs. Contrary to cre gene expression in Trichoderma reesei and Aspergillus nidulans, the transcript level of the cre1 gene from an A. chrysogenum wild-type strain is increased in the presence of glucose. Remarkably, the glucose-dependent transcriptional upregulation does not take place in another A. chysogenum strain, which displays enhanced production of the beta-lactam antibiotic cephalosporin C. We surmise that the de-regulation of cre1 is connected with the increased production rate in this strain.

On-line and off-line monitoring of the production of cephalosporin C by Acremonium chrysogenum

Process monitoring of cephalosporin C formation by Acremonium chrysogenum in laboratory investigations is considered. The goal of these investigations is the identification of bottlenecks in the biosynthesis and the improvement of the process performance. Based on reports of other research groups and own experience the key parameters were selected, which influence the process performance. They are: dissolved oxygen and pH values. In addition the concentrations of biomass, DNA, glucose and reducing sugars (glucose, maltose, maltotriose and oligosaccharides), methionine, other nitrogen sources (ammonium ion, other amino acids), organic acids, phosphate, sulfate, dissolved organic carbon, proteins, product and precursors in the cell free cultivation medium are monitored. In addition the intracellular concentrations of RNA, DNA, proteins, amino acids as well as the activities of the enzymes of the biosynthesis of cephalosporin C are determined. The influence of these parameters on the biosynthesis is discussed.

Further studies on the bioconversion of penicillin G into deacetoxycephalosporin G by resting cells of Streptomyces clavuligerus NP-1

Resting cells of Streptomyces clavuligerus NP-1, which possess deacetoxycephalosporin C synthase activity, have been shown previously to perform oxidative ring expansion of penicillin G in the presence of iron, ascorbic acid, and alpha-ketoglutaric acid to form deacetoxycephalosporin G. Further studies on this bioconversion indicated that use of MOPS or HEPES buffer at pH 6.5 more than doubled the extent of the reaction observed with the previously used Tris-HCl at pH 7.4. Levels of bioconversion as high as 16.5% were achieved at low penicillin G concentrations. Previously, conversion yields were < 1%.

The NADP-dependent glutamate dehydrogenase gene from Penicillium chrysogenum and the construction of expression vectors for filamentous fungi

The gdhA gene encoding the NADP-dependent glutamate dehydrogenase activity from Penicillium chrysogenum has been isolated and characterized for its use in gene expression. The nucleotide sequence of a 2816-bp genomic fragment was determined, showing an open reading frame of 1600 bp interrupted by two introns, of 160 bp and 57 bp respectively, with fungal consensus splice-site junctions. The predicted amino acid sequence revealed a high degree of identity to glutamate dehydrogenase enzymes, especially to those from the fungi Aspergillus nidulans (82%) and Neurospora crassa (78%). The gdhA gene was found to be present in a single copy in the genome of several P. chrysogenum strains with different penicillin productivity. The use of the gdhA promoter for homologous and heterologous gene expression in fungi and Escherichia coli was analyzed. Heterologous gene expression was ascertained by the construction of gene fusions with the lacZ gene from E. coli and the bleomycin-resistance determinant (bleR) from Streptoalloteichus hindustanus. Homologous gene expression was shown through the use of the penicillin-biosynthetic genes pchC and penDE from P. chrysogenum and the cephalosporin biosynthetic genes cefEF and cefG from Acremonium chrysogenum.

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.

D-amino acid oxidase: its potential in the production of 7-aminocephalosporanic acid

D-Amino acid oxidase (DAAO) used in the preparation of alpha-keto acids, in the determination of D-amino acids and in the resolution of racemic mixture of amino acids is produced by a wide range of microorganisms. In the recent past this enzyme is being recognized for its potential in the commercial production of 7-aminocephalosporanic acid (7-ACA), a starting material for various semisynthetic cephalosporins. Though this enzyme is widespread among microorganisms, very few microbial species have been explored for the production of 7-ACA; this is because cephalosporin C is quantitatively deaminated by limited microbial DAAOs. Comparison of physico-chemical properties of enzyme preparations indicate wide variations, however in general DAAOs are specific for D-configuration of amino acids. Both immobilized enzyme and cell preparations are developed for its various applications. The advantages of DAAO in the production of 7-ACA are discussed.

Cephalosporin C production by Cephalosporium acremonium: the methionine story

More than 40 years ago, it was reported that methionine markedly stimulated production of cephalosporin C by Cephalosporium acremonium. Over the years, many hypotheses were put forth to explain this phenomenon. The accumulating evidence strongly supported the concept that methionine stimulates by inducing enzymes of the biosynthetic pathway such as delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine synthetase, isopenicillin N synthase, and deacetoxycephalosporin C synthase. This mechanism has been strengthened by the finding that transcription of the genes encoding the above enzymes is markedly enhanced by growth with methionine. An effect of methionine in the fermentation unrelated to the titer stimulation is its contribution of the sulfur atom to the cephalosporin molecule. Methionine also stimulates mycelial fragmentation; the relationship between this effect on hyphal differentiation and the induction of the cephalosporin synthases remains to be elucidated.

Transcriptional control of expression of fungal beta-lactam biosynthesis genes

The most commonly used beta-lactam antibiotics for the therapy of infectious diseases are penicillin and cephalosporin. Penicillin is produced as end product by some fungi most notably by Aspergillus (Emericella) nidulans and Penicillium chrysogenum. Cephalosporins are synthesised by several bacteria and fungi, e.g. by the fungus Acremonium chrysogenum (syn. 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. The penicillin biosynthesis is catalysed by three enzymes encoded by acvA (pcbAB), ipnA (pcbC) and aatA (penDE). The genes are organised into a cluster. In A. chrysogenum, in addition to acvA and ipnA, which are also clustered, a second cluster contains the genes for enzymes catalysing the reactions of the later steps of the cephalosporin pathway (cefEF, cefG). Transcription of biosynthesis genes is subject to sophisticated control by nutritional factors (e.g. glucose, nitrogen), amino acids such as lysine and methionine, and ambient pH. Some regulators have been identified such as the A. nidulans pH regulatory protein PACC and the transcriptional complex PENR1. PENR1 is a HAP-like transcriptional complex similar or identical to AnCF. Additional positive regulatory factors seem to be represented by recessive trans-acting mutations of A. nidulans (prgA1, prgB1, npeE1) and P. chrysogenum (carried by mutants Npe2 and Npe3). The GATA-binding factor NRE appears to be involved in the regulation of the penicillin biosynthesis genes by the nitrogen source in P. chrysogenum. Formal genetic evidence suggests the existence of transcriptional repressors as well.

Penicillin and cephalosporin biosynthesis: mechanism of carbon catabolite regulation of penicillin production

Penicillins and cephalosporins are synthesized by a series of enzymatic reactions that form the tripeptide delta-(L-alpha-aminoadipyl)-L-cysteinyl-D-valine and convert this tripeptide into the final penicillin or cephalosporin molecules. One of the enzymes, isopenicillin N synthase has been crystallyzed and its active center identified. The three genes pcbAB, pcbC and penDE involved in penicillin biosynthesis are clustered in Penicillium chrysogenum, Aspergillus nidulans and Penicillium nalgiovense. Carbon catabolite regulation of penicillin biosynthesis is exerted by glucose and other easily utilizable carbon sources but not by lactose. The glucose effect is enhanced by high phosphate concentrations. Glucose represses the biosynthesis of penicillin by preventing the formation of the penicillin biosynthesis enzymes. Transcription of the pcbAB, pcbC and penDE genes of P. chrysogenum is strongly repressed by glucose and the repression is not reversed by alkaline pHs. Carbon catabolite repression of penicillin biosynthesis in A. nidulans is not mediated by CreA and the same appears to be true in P. chrysogenum. The first two genes of the penicillin pathway (pcbAB and pcbC) are expressed from a bidirectional promoter region. Analysis of different DNA fragments of this bidirectional promoter region revealed two important DNA sequences (boxes A and B) for expression and glucose catabolite regulation of the pcbAB gene. Using protein extracts from mycelia grown under carbon catabolite repressing or derepressing conditions DNA-binding proteins that interact with the bidirectional promoter region were purified to near homogeneity.

Allosamidin inhibits the fragmentation of Acremonium chrysogenum but does not influence the cephalosporin-C production of the fungus

The pseudotrisaccharide allosamidin, a potent inhibitor of chitinases, retarded the fragmentation of hyphae but did not affect the fungal growth and cephalosporin-C production in Acremonium chrysogenum. In vitro inhibition of A. chrysogenum cell-bound chitinase(s) by allosamidin revealed that about 47% of the soluble intracellular chitinase activity was resistant to the inhibitory effect of allosamidin. On the other hand, about 76% of the total chitinase activity localised in both the soluble and insoluble enzyme fractions was effectively inhibited by allosamidin. All the chitinase activities were measured using a new procedure based on purified A. chrysogenum chitin as substrate.

New aspects of genes and enzymes for beta-lactam antibiotic biosynthesis

Penicillins, cephalosporins and cephamycins are peptide antibiotics synthesized by condensation of L-alpha-aminoadipic acid, L-cysteine and L-valine to form the tripeptide delta(L-alpha-aminoadipyl)-L-cysteinyl-D-valine (Aad-Cys-Val) by a non-ribosomal peptide synthetase. The genes pcbAB and pcbC, common to all penicillin and cephalosporin producers, that encode the Aad-Cys-Val synthetase and isopenicillin N (IPN) synthase respectively, have been cloned and the encoded enzymes studied in detail. The IPN synthase has been crystallized and its active center identified, providing evidence for the molecular mechanism of cyclization of the tripeptide Aad-Cys-Val to isopenicillin N. The late genes of the penicillin and cephalosporin pathways have also been characterized although some of the molecular mechanisms catalyzed by the encoded enzymes (e.g. IPN acyltransferase) are still obscure. In cephamycin-producing organisms, biosynthesis of the alpha-aminoadipic acid precursor proceeds in two steps catalyzed by lysine 6-aminotransferase and piperideine-6-carboxylic acid dehydrogenase. The gene lat for the first of these enzymes is located in the cephamycin gene cluster, providing an interesting example of association of genes encoding enzymes for the formation of a precursor with genes involved in assembly of the antibiotics. Novel enzymes involved in methoxylation at C-7 and carbamoylation at C-3' of the cephem nucleus were isolated from Nocardia lactamdurans and Streptomyces clavuligerus. The methoxylation system is encoded by two linked genes cmcI-cmcJ and their products (proteins P7 and P8) form a complex that is required for hydroxylation at C-7 and for the subsequent methylation of the 7-hydroxycephem derivative to form the methoxyl group. Carbamoylation at the C-3'-hydroxyl group of the cephem nucleus is catalyzed by a specific carbamoyltransferase encoded by the gene cmcH. Finally, genes for a beta-lactamase (bla), a penicillin-binding protein (pbp) and a transmembrane protein (cmcT) that appears to be involved in cephamycin exportation, are clustered together with the biosynthetic genes in the cephamycin clusters of S. clavuligerus and N. lactamdurans. Availability of the cloned genes allows metabolic engineering of the beta-lactam biosynthetic pathways such as a channelling precursors and directed removal of bottlenecks in the beta-lactam biosynthetic pathways. Several new beta-lactam antibiotics have been discovered in gram-positive and gram-negative bacteria that will provide new genes for combinatorial synthesis of new molecules.

Process models for production of beta-lactam antibiotics

Great progress has been made in the modelling of biotechnical processes using filamentous microorganisms. This paper deals with cultivations of Penicillium chrysogenum for the production of Penicillin and of Acremonium chrysogenum for the production of Cephalosporin C. The properties of the processes and the existing models are reviewed. Models are presented for both processes that consider aspects which are important for industrial cultivation. The process model for Penicillin production is based on a detailed morphological description of growth of hyphal filaments and pellets. The model allows for simulation of the production process including the preculture and considering the inhomogenous pellet population. It opens new possibilities for understanding the complex kinetics of the process and improvement of its control. The structured segregated model for Cephalosporin C production considers soy oil as second carbon source besides sugar. The application of the model for dynamic optimization of feeding strategies by Iterative Dynamic Programming is demonstrated. As an alternative approach, modelling of the Cephalosporin production by an artificial neural network is discussed.

Enzymatic synthesis of diastereospecific carbacephem intermediates using serine hydroxymethyltransferase

The serine hydroxymethyltransferase (SHMT) gene glyA was over-expressed in Escherichia coli and the enzyme was purified to near homogeneity. Reaction conditions for E. coli and rabbit liver SHMTs were optimized using succinic semialdehyde methyl ester (SSAME) and glycine. The catalytic efficiency (kcat/K(m)) of E. coli SHMT for SSAME was 2.8-fold higher than that of rabbit liver enzyme. E. coli SHMT displayed a pH-dependent product distribution different from that of rabbit liver enzyme. For the pyridoxal-5'-phosphate (PLP)-dependent reaction, E. coli and rabbit liver SHMTs showed a high product diastereospecificity. The stoichiometric ratio of PLP to the dimeric E. coli SHMT was 0.5-0.7, indicating a requirement for external PLP for maximal activity. Using SSAME or its analog at a high temperature, E. coli SHMT mediated efficient condensation via a lactone pathway. In contrast, at a low temperature, the enzyme catalyzed efficient conversion of 4-penten-1-al via a non-lactone mechanism. Efficient conversion of either aldehyde type to a desirable diastereospecific product was observed at a pilot scale. E. coli SHMT exhibited a broad specificity toward aldehyde substrates; thus it can be broadly useful in chemo-enzymatic synthesis of a chiral intermediate in the manufacture of an important carbacephem antibiotic.

Expression of the cefG gene is limiting for cephalosporin biosynthesis in Acremonium chrysogenum

The conversion of deacetylcephalosporin C to cephalosporin C is inefficient in most Acremonium chrysogenum strains. The cefG gene, which encodes deacetylcephalosporin C acetyltransferase, is expressed very poorly in A. chrysogenum as compared to other genes of the cephalosporin pathway. Introduction of additional copies of the cefG gene with its native promoter (in two different constructions with upstream regions of 1056 bp and 538 bp respectively) did not produce a significant increase of the steady-state level of the cefG transcript. Expression of the cefG gene from the promoters of (i) the glyceraldehyde-3-phosphate dehydrogenase (gpd) gene of Aspergillus nidulans, (ii) the glucoamylase (gla) gene of Aspergillus niger, (iii) the glutamate dehydrogenase (gdh) and (iv) the isopenicillin N synthase (pcbC) genes of Penicillium chrysogenum, led to very high steady-state levels of cefG transcript and to increased deacetylcephalosporin-C acetyltransferase protein concentration (as shown by immunoblotting) and enzyme activity in the transformants. Southern analysis showed that integration of the new constructions occurred at sites different from that of the endogenous cefG gene. Cephalosporin production was increased two- to threefold in A. chrysogenum C10 transformed with constructions in which the cefG gene was expressed from the gdh or gpd promoters as a result of a more efficient acetylation of deacetylcephalosporin C.

Evolving enzyme technology for pharmaceutical applications: case studies

The case studies focus on two types of enzyme applications for pharmaceutical development. Demethylmacrocin O-methyltransferase, macrocin O-methyltransferase (both putatively rate-limiting) and tylosin reductase were purified from Streptomyces fradiae, characterized and the genes manipulated for increasing tylosin biosynthesis in S. fradiae. The rate-limiting enzyme, deacetoxycephalosporin C (DAOC) synthase/hydroxylase (expandase/ hydroxylase), was purified from Cephalosporium acremonium, its gene over-expressed, and cephalosporin C biosynthesis improved in C. acremonium. Also, heterologous expression of penicillin N epimerase and DAOC synthase (expandase) genes of Streptomyces clavuligerus in Penicillium chrysogenum permitted DAOC production in the fungal strain. Second, serine hydroxymethyltransferase of Escherichia coli and phthalyl amidase of Xanthobacter agilis were employed in chemo-enzymatic synthesis of carbacephem. Similarly, echinocandin B deacylase of Actinoplanes utahensis was used in the second-type synthesis of the ECB antifungal agent.

Partial purification, characterization and nitrogen regulation of the lysine epsilon-aminotransferase of Streptomyces clavuligerus

The L-lysine epsilon-aminotransferase (LAT) of Streptomyces clavuligerus was partially purified and characterized. The 51.3-kDa enzyme exhibited optimal activity at pH 7.0-7.5 and 30 degrees C. It catalyzed transfer of the terminal amino group of L-lysine or L-ornithine to alpha-ketoglutarate. Oxalacetate and pyruvate were also used as acceptors of the amino group but with very low efficiency. Increasing ammonium concentrations added to chemically-defined medium MM enhanced the formation of LAT and decreased production of cephalosporins by S. clavuligerus. In cultures grown in the absence of lysine, greater enhancement of LAT formation by ammonium and less repression of cephalosporin biosynthesis were observed. In the chemically-defined GSPG medium, ammonium ions decreased cephalosporin production without showing an effect on LAT formation.

Lysine epsilon-aminotransferase, the initial enzyme of cephalosporin biosynthesis in actinomycetes

Streptomyces clavuligerus, Streptomyces lipmanii and Nocardia (formerly Streptomyces) lactamdurans are Gram-positive mycelial bacteria that produce medically important beta-lactam antibiotics (penicillins and cephalosporins including cephamycins) that are synthesized through a series of reactions starting from lysine, cysteine and valine. L-lysine epsilon-aminotransferase (LAT) is the initial enzyme in the two-step conversion of L-lysine to L-alpha-aminoadipic acid, a specific precursor of all penicillins and cephalosporins. Whereas S. clavuligerus uses LAT for cephalosporin production, it uses the cadaverine pathway for catabolism when lysine is the nitrogen source for growth. Although the cadaverine path is present in all examined streptomycetes, the LAT pathway appears to exist only in beta-lactam-producing strains. Genetically increasing the level of LAT enhances the production of cephamycin. LAT is the key rate-limiting enzyme in cephalosporin biosynthesis in S. clavuligerus strain NRRL 3585. This review will summarize information on this important enzyme.

Secondary metabolism in simulated microgravity: beta-lactam production by Streptomyces clavuligerus

Rotating bioreactors designed at NASA's Johnson Space Center were used to simulate a microgravity environment in which to study secondary metabolism. The system examined was beta-lactam antibiotic production by Streptomyces clavuligerus. Both growth and beta-lactam production occurred in simulated microgravity. Stimulatory effects of phosphate and L-lysine, previously detected in normal gravity, also occurred in simulated microgravity. The degree of beta-lactam antibiotic production was markedly inhibited by simulated microgravity.

The inhibitory mechanisms of glucose and carbon dioxide on the biosyntheses of penicillins and cephalosporins

The inhibitory mechanism of glucose and CO2 on the biosyntheses of penicillins and cephalosporins is discussed in the present paper. 6-aminopenicillanic acid (6-APA) is considered to be an intermediate product, and the reaction between 6-APA and glucose may play an important role in the yield and rate of biosyntheses of beta-lactam antibiotics. According to this hypothesis the experimental phenomena taking place in biosynthesis of penicillin and cephalosporin, such as the inhibition by glucose and carbon dioxide and the reduction of the yield, can be satisfactorily explained. The stability of 6-aminopenicillanic acid (6-APA) in bicarbonate solution, the reaction of 6-APA with sugars, the determination of the concentration of the 6-APA-sugar compound and the effect of these reactions on the biosynthesis of penicillin G are investigated to present evidences for this hypothesis.