Enhanced FK506 production in Streptomyces clavuligerus CKD1119 by engineering the supply of methylmalonyl-CoA precursor

An erythromycin process improvement using the diethyl methylmalonate-responsive (Dmr) phenotype of the Saccharopolyspora erythraea mutB strain

The Saccharopolyspora erythraea mutB knockout strain, FL2281, having a block in the methylmalonyl-CoA mutase reaction, was found to carry a diethyl methylmalonate-responsive (Dmr) phenotype in an oil-based fermentation medium. The Dmr phenotype confers the ability to increase erythromycin A (erythromycin) production from 250-300% when the oil-based medium is supplemented with 15 mM levels of this solvent. Lower concentrations of the solvent stimulated proportionately less erythromycin production, while higher concentrations had no additional benefit. Although the mutB strain is phenotypically a low-level erythromycin producer, diethyl methylmalonate supplementation allowed it to produce up to 30% more erythromycin than the wild-type (control) strain-a strain that does not show the Dmr phenotype. The Dmr phenotype represents a new class of strain improvement phenotype. A theory to explain the biochemical mechanism for the Dmr phenotype is proposed. Other phenotypes found to be associated with the mutB knockout were a growth defect and hyper-pigmentation, both of which were restored to normal by exposure to diethyl methylmalonate. Furthermore, mutB fermentations did not significantly metabolize soybean oil in the presence of diethyl methylmalonate. Finally, a novel method is proposed for the isolation of additional mutants with the Dmr phenotype.

Enhanced production of ansamitocin P-3 by addition of Mg2+ in fermentation of Actinosynnema pretiosum

The effect of divalent metal ions (i.e., Mn(2+), Mg(2+), Zn(2+), Cu(2+), and Co(2+)) on the production of anticancer ansamitocin P-3 (AP-3) by submerged cultures of Actinosynnema pretiosum in medium containing agro-industrial residues was investigated, and Mg(2+) was found to be the most effective. Under the optimal condition of Mg(2+) addition, the maximal AP-3 production titer reached 85 mg/L, which was 3.0-fold that of the control. The activities of methylmalonyl-CoA carboxyltransferase (MCT) and methylmalonyl-CoA mutase (MCM) were enhanced. The content of two precursors, malonyl-CoA and methylmalonyl-CoA, was lower than that of control. This work demonstrates that Mg(2+) addition is a simple and effective strategy for increasing AP-3 production through the regulation of enzyme activity and pools of precursors. The information obtained can be helpful to its efficient production on large scale.

A combined approach of classical mutagenesis and rational metabolic engineering improves rapamycin biosynthesis and provides insights into methylmalonyl-CoA precursor supply pathway in Streptomyces hygroscopicus ATCC 29253

Rapamycin is a macrocyclic polyketide with immunosuppressive, antifungal, and anticancer activity produced by Streptomyces hygroscopicus ATCC 29253. Rapamycin production by a mutant strain (UV2-2) induced by ultraviolet mutagenesis was improved by approximately 3.2-fold (23.6 mg/l) compared to that of the wild-type strain. The comparative analyses of gene expression and intracellular acyl-CoA pools between wild-type and the UV2-2 strains revealed that the increased production of rapamycin in UV2-2 was due to the prolonged expression of rapamycin biosynthetic genes, but a depletion of intracellular methylmalonyl-CoA limited the rapamycin biosynthesis of the UV2-2 strain. Therefore, three different metabolic pathways involved in the biosynthesis of methylmalonyl-CoA were evaluated to identify the effective precursor supply pathway that can support the high production of rapamycin: propionyl-CoA carboxylase (PCC), methylmalonyl-CoA mutase, and methylmalonyl-CoA ligase. Among them, only the PCC pathway along with supplementation of propionate was found to be effective for an increase in intracellular pool of methylmalonyl-CoA and rapamycin titers in UV2-2 strain (42.8 mg/l), indicating that the PCC pathway is a major methylmalonyl-CoA supply pathway in the rapamycin producer. These results demonstrated that the combined approach involving traditional mutagenesis and metabolic engineering could be successfully applied to the diagnosis of yield-limiting factors and the enhanced production of industrially and clinically important polyketide compounds.

Biosynthesis of rapamycin and its regulation: past achievements and recent progress

Rapamycin and its analogs are clinically important macrolide compounds produced by Streptomyces hygroscopicus. They exhibit antifungal, immunosuppressive, antitumor, neuroprotective and antiaging activities. The core macrolactone ring of rapamycin is biosynthesized by hybrid type I modular polyketide synthase (PKS)/nonribosomal peptide synthetase systems primed with 4,5-dihydrocyclohex-1-ene-carboxylic acid. The linear polyketide chain is condensed with pipecolate by peptide synthetase, followed by cyclization to form the macrolide ring and modified by a series of post-PKS tailoring steps. The aim of this review was to outline past and recent advances in the biosynthesis and regulation of rapamycin, with an emphasis on the distinguished contributions of Professor Demain to the study of rapamycin. In addition, this article describes the biological activities as well as mechanism of action of rapamycin and its derivatives. Recent attempts to improve the productivity of rapamycin and generate diverse rapamycin analogs through mutasynthesis and mutagenesis are also introduced, along with some future perspectives.