Coordination of glycerol utilization and clavulanic acid biosynthesis to improve clavulanic acid production in Streptomyces clavuligerus

The glycerol utilization (gyl) operon is involved in clavulanic acid (CA) production by Streptomyces clavuligerus, and possibly supplies the glyceraldehyde-3-phosphate (G3P) precursor for CA biosynthesis. The gyl operon is regulated by GylR and is induced by glycerol. To enhance CA production in S. clavuligerus, an extra copy of ccaR expressed from Pgyl (the gyl promoter) was integrated into the chromosome of S. clavuligerus NRRL 3585. This construct coordinated the transcription of CA biosynthetic pathway genes with expression of the gyl operon. In the transformants carrying the Pgyl-controlled regulatory gene ccaR, CA production was enhanced 3.19-fold in glycerol-enriched batch cultures, relative to the control strain carrying an extra copy of ccaR controlled by its own promoter (PccaR). Consistent with enhanced CA production, the transcription levels of ccaR, ceas2 and claR were significantly up-regulated in the transformants containing Pgyl-controlled ccaR.

Proteome-wide alterations in an industrial clavulanic acid producing strain of Streptomyces clavuligerus

The usefulness of genetic/metabolic engineering for further improvement of industrial strains is subject of discussion because of the general lack of knowledge on genetic alterations introduced by iterative cycles of random mutagenesis in such strains.An industrial clavulanic acid(CA)-overproducer Streptomyces clavuligerus DEPA was assessed to understand proteome-wide changes that have occurred in a local industrial CA overproducer developed through succesive mutagenesis programs.The proteins that could be identified corresponded to 33 distinct ORFs for underrepresented ones and 60 ORFs for overrepresented ones.Three CA biosynthetic enzymes were overrepresented in S.clavuligerus DEPA;carboxyethylarginine synthase(Ceas2),clavaldehyde dehydrogenase(Car)and carboxyethyl-arginine betalactam-synthase(Bls2)whereas the enzymes of two other secondary metabolites were underrepresented along with two important global regulators[two-component system(TCS)response regulator(SCLAV_2102)and TetR-family transcriptional regulator(SCLAV_3146)]that might be related with CA production and/or differentiation.g-butyrolactone biosynthetic protein AvaA2 was 2.6 fold underrepresented in S.clavuligerus DEPA.The levels of two glycolytic enzymes,2,3-bisphosphoglycerate-dependent phosphoglycerate mutase and phosophoglycerate kinase were found decreased while those of dihydrolipoyl dehydrogenase(E3)and isocitrate dehydrogenase,with two isoforms were found as significantly increased.A decrease of amino acid metabolism,methionine biosynthesis in particular,as well as S-adenosylmethionine synthetase appeared as one of the prominent mechanisms of success of S.clavuligerus DEPA strain as a prolific producer of CA.The levels of two enzymes of shikimate pathway that leads to the production of aromatic amino acids and aromatic secondary metabolites were also underrepresented.Some of the overrepresented stress proteins in S.clavuligerus DEPA included polynucleotide phosphorylase/polyadenylase(PNPase),ATP-dependent DNA helicase,two isoforms of an anti-sigma factor and thioredoxin reductase.Downregulation of important proteins of cell wall synthesis and division was recorded and a protein with b-lactamase domain(SCLAV_p1007)appeared in 12 isoforms,5 of which were drastically overrepresented in DEPA strain.These results described herein provide useful information for rational engineering to improve CA production in Streptomyces clavuligerus.

Deacetoxycephalosporin C synthase(expandase):Research progress and application potential

Cephalosporins play an indispensable role against bacterial infections.Deacetyloxycephalosporin C synthase(DAOCS),also called expandase,is a key enzyme in cephalosporin biosynthesis that epoxides penicillin to form the hexavalent thiazide ring of cephalosporin.DAOCS in fungus Acremonium chrysogenum was identified as a bifunctional enzyme with both ring expansion and hydroxylation,whereas two separate enzymes in bacteria catalyze these two reactions.In this review,we briefly summarize its source and function,improvement of the conversion rate of penicillin to deacetyloxycephalosporin C through enzyme modification,crystallography features,the prediction of the active site,and application perspective.

Development of a colorimetric assay for rapid quantitative measurement of clavulanic acid in microbial samples

We developed a colorimetric assay to quantify clavulanic acid （CA） in culture broth of Streptomyces clavuligerus, to facilitate screening of a large number of S. clavuligerus mutants. The assay is based on a β-1actamase-catalyzed reaction, in which the yellow substrate nitrocefin （λmax=390 nm） is converted to a red product （λmax=486 nm）. Since CA can irreversibly inhibit β-1actamase activity, the level of CA in a sample can be measured as a function of the A390]A486 ratio in the assay mixture. The sensitivity and detection window of the assay were determined to be 50 μg L -1 and 50 μg L to 10 mg L-1, respectively. The reliability of the assay was confirmed by comparing assay results with those obtained by HPLC. The assay was used to screen a pool of 65 S. clavuligerus mutants and was reliable for identifying CA over-producing mutants. Therefore, the assay saves time and labor in large-scale mutant screening and evaluation tasks. The detection window and the reliability of this assay are markedly better than those of previously reported CA assays. This assay method is suitable for high throughput screening of microbial samples and allows direct visual observation of CA levels on agar plates.