Direct fermentative production of acyltylosins by genetically-engineered strains of Streptomyces fradiae

The regulatory genes involved in spiramycin and bitespiramycin biosynthesis

Bitespiramycin (biotechnological spiramycin, Bsm) is a new 16-membered macrolide antibiotic produced by Streptomyces spiramyceticus WSJ-1 integrated exogenous genes. The gene cluster for Bsm biosynthesis consists of two parts: spiramycin biosynthetic gene cluster (92 kb) and two exogenous genes including 4"-O-isovaleryltransferase gene (ist) and a positive regulatory gene (acyB2) from S. thermotolerans. Four putative regulatory genes, bsm2, bsm23, bsm27 and bsm42, were identified by sequence analysis in the spiramycin gene cluster. The inactivation of bsm23 or bsm42 in S. spiramyceticus eliminated spiramycin production, while the deletion of bsm2 and bsm27 did not abolish spiramycin biosynthesis. The acyB2 gene, homologous with bsm42 gene, cannot recover the spiramycin production in Δbsm42 mutant. The high expression of bsm42 significantly increased the spiramycin production, but overexpression of bsm23 inhibited its production in Δbsm23 and wild-type strain. Bsm23 was shown to be involved in the regulation of the expression of bsm42 and acyB2 by electrophoretic mobility shift assays. The bsm42 gene was also positive regulator for ist expression inferred from the improved yield of 4"-isovalerylspiramycins in the S. lividans TK24 biotransformation test, but adding bsm23 decreased the production of 4''-isovalerylspiramycins. These results demonstrated Bsm42 was a pathway-specific activator for spiramycin or Bsm biosynthesis, but overexpression of Bsm23 alone was adverse to produce these antibiotics although Bsm23 was essential for positive regulation of spiramycin production.

Identification of two regulatory genes involved in carbomycin biosynthesis in Streptomyces thermotolerans

Carbomycins are 16-membered macrolide antibiotics produced by Streptomyces thermotolerans ATCC 11416^T. To characterize gene cluster responsible for carbomycin biosynthesis, the draft genome sequences for strain ATCC 11416^T were obtained, from which the partial carbomycin biosynthetic gene cluster was identified. This gene cluster was approximately 40 kb in length, and encoding 30 ORFs. Two putative transcriptional regulatory genes, acyB2 and cbmR, were inactivated by insertion of the apramycin resistance gene, and the resulting mutants were unable to produce carbomycin, thus confirming the involvement of two regulatory genes in carbomycin biosynthesis. Overexpression of acyB2 greatly improved the yield of carbomycin; however, overexpression of cbmR blocked carbomycin production. The qPCR analysis of the carbomycin biosynthetic genes in various mutants indicated that most genes were highly expressed in acyB2-overexpressing strains, but few expressed in cbmR-overexpressing strains. Furthermore, acyB2 co-expression with 4″-isovaleryltransferase gene (ist), resulted in efficient biotransformation of spiramycin into bitespiramycin in S. lividans TK24, whereas ist gene regulated by acyB2 and cbmR would cause the lower efficiency of spiramycin biotransformation. These results indicated that AcyB2 was a pathway-specific positive regulator of carbomycin biosynthesis. However, CbmR played a dual role in the carbomycin biosynthesis by acting as a positive regulator, and as a repressor at cbmR high expression levels.

Pursuing the unlimited potential of microorganisms—progress and prospect of a fermentation company†

Production of pharmaceuticals and chemicals using microbial functions has bestowed numerous benefits onto society. The Nobel Prize awarded to Professor Ōmura, Distinguished Emeritus Professor of Kitasato University, showed the world the importance of the discovery and practical application of microorganisms. Now, increasing attention is turned toward the future path of this field. As people involved in the microorganism industry, we will review the industrial activities thus far and consider the possible future developments in this field and its potential contribution to society.

Immobilization of Streptomyces thermotolerans 11432 on polyurethane foam to improve production of acetylisovaleryltylosin

In this study, polyurethane foam (PUF) was chemically treated to immobilize Streptomyces thermotolerans 11432 for semi-continuous production of acetylisovaleryltylosin (AIV). Based on experimental results, positive cross-linked PUF (PCPUF) was selected as the most effective carrier according to immobilized cell mass. The effect of adsorption time on immobilized mass was investigated. AIV concentration (33.54 mg/l) in batch fermentations with immobilized cells was higher than with free cells (20.34 mg/l). In repeated batch fermentations with immobilized S. thermotolerans 11432 using PCPUF cubes, high AIV concentrations and conversion rates were attained, ranging from 25.56 to 34.37 mg/l and 79.93 to 86.31 %, respectively. Significantly, this method provides a feasible strategy for efficient AIV production and offers the potential for large-scale production.

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.

Recombinant organisms for production of industrial products

A revolution in industrial microbiology was sparked by the discoveries of ther double-stranded structure of DNA and the development of recombinant DNA technology. Traditional industrial microbiology was merged with molecular biology to yield improved recombinant processes for the industrial production of primary and secondary metabolites, protein biopharmaceuticals and industrial enzymes. Novel genetic techniques such as metabolic engineering, combinatorial biosynthesis and molecular breeding techniques and their modifications are contributing greatly to the development of improved industrial processes. In addition, functional genomics, proteomics and metabolomics are being exploited for the discovery of novel valuable small molecules for medicine as well as enzymes for catalysis. The sequencing of industrial microbal genomes is being carried out which bodes well for future process improvement and discovery of new industrial products.

Effect of branched-chain amino acids, valine, isoleucine and leucine on the biosythesis of bitespiramycin 4"-O-acylspiramycins

Bitespiramycin, a group of 4"-O-acylated spiramycins with 4"-O-isovalerylspiramycins as the major components, was produced by recombinant spiramycin-producing strain Streptomyces spiramyceticus harboring a 4"-O-acyltransferase gene. The experiment was initially performed in synthetic medium with 0.5 g l(-1) Valine, Isoleucine or Leucine feeding at 36 h cultivation. When valine was fed, the biological titer of bitespiramycin was 45.3% higher than that of the control group, but the relative content of total isovalerylspiramycin components decreased by 22.5%. In the case of ilecine, the biological titer of bitespiramycin and the total isovalerylspiramycins alone were 85% and 72.1% of the control group, respectively. In contrast, the relative content of other acylated spiramycins increased by 54.41%. However, leucine feeding increased the relative content of total isovalerylspiramycins by 41.9% while the biological titer of bitespiramycin was nearly equal to that of the control group. The improvement effect of leucine on the biosynthesis of isovalerylspiramycins was further confirmed by feeding of 2.0 g l(-1) leucine to the culture with complex medium. After batch feeding with a total amount of 2.0 g l(-1) leucine to the culture from 70 h to 90 h, the biological titer of bitespiramycin was almost unreduced, and the final relative content of total isovalerylspiramycins increased from 31.1% to 46.9%.

Application of a newly identified and characterized 18-o-acyltransferase in chemoenzymatic synthesis of selected natural and nonnatural bioactive derivatives of phoslactomycins

Phoslactomycins (PLMs) and related leustroducsins (LSNs) have been isolated from a variety of bacteria based on antifungal, anticancer, and other biological assays. Streptomyces sp. strain HK 803 produces five PLM analogs (PLM A and PLMs C to F) in which the C-18 hydroxyl substituent is esterified with a range of branched, short-alkyl-chain carboxylic acids. The proposed pathway intermediate, PLM G, in which the hydroxyl residue is not esterified has not been observed at any significant level in fermentation, and the only route to this potentially useful intermediate has been an enzymatic deacylation of other PLMs and LSNs. We report that deletion of plmS(3) from the PLM biosynthetic cluster gives rise to a mutant which accumulates the PLM G intermediate. The 921-bp plmS(3) open reading frame was cloned and expressed as an N-terminally polyhistidine-tagged protein in Escherichia coli and shown to be an 18-O acyltransferase, catalyzing conversion of PLM G to PLM A, PLM C, and PLM E using isobutyryl coenzyme A (CoA), 3-methylbutyryl-CoA, and cyclohexylcarbonyl-CoA, respectively. The efficiency of this process (k(cat) of 28 +/- 3 min(-1) and K(m) of 88 +/- 16 microM) represents a one-step chemoenzymatic alternative to a multistep synthetic process for selective chemical esterification of the C-18 hydroxy residue of PLM G. PlmS(3) was shown to catalyze esterification of PLM G with CoA and N-acetylcysteamine thioesters of various saturated, unsaturated, and aromatic carboxylic acids and thus also to provide an efficient chemoenzymatic route to new PLM analogs.

Leucine improves the component of isovalerylspiramycins for the production of bitespiramycin

Bitespiramycin, a group of 4''-O-acylated spiramycins with 4''-O-isovalerylspiramycins as the major components, is produced by recombinant spiramycin-producing strain Streptomyces spiramyceticus harboring a 4''-O-acyltransferase gene from a carbomycin-producing strain S. mycarofaciens 1748. The effects of leucine feeding on the bitespiramycin fermentation, especially the synthesis of isovalerylspiramycin components, were investigated. The experiment was initially performed in flask culture under the condition of feeding 15.4 mmol/l of leucine at 72 h fermentation, and the culture without leucine feeding was used as control. When 15.4 mmol/l leucine was fed at 72 h, 51.3 +/- 0.33% total isovalerylspiramycins was recorded compared to 40.9 +/- 0.26% under the control condition after 96 h of fermentation. The improvement of total isovalerylspiramycin content was further achieved in 15 l fermentation when 15.4 mmol/l of leucine was supplemented from 65 to 72 h. These results indicated that isovaleryl group derived from leucine catabolism could act as the precursor of the 4'' side chain of bitespiramycin, which profoundly enhanced the synthesis of isovalerylspiramycins in the bitespiramycin complex.

Contributions of microorganisms to industrial biology

Life on earth is not possible without microorganisms. Microbes have contributed to industrial science for over 100 years. They have given us diversity in enzymatic content and metabolic pathways. The advent of recombinant DNA brought many changes to industrial microbiology. New expression systems have been developed, biosynthetic pathways have been modified by metabolic engineering to give new metabolites, and directed evolution has provided enzymes with modified selectability, improved catalytic activity and stability. More and more genomes of industrial microorganisms are being sequenced giving valuable information about the genetic and enzymatic makeup of these valuable forms of life. Major tools such as functional genomics, proteomics, and metabolomics are being exploited for the discovery of new valuable small molecules for medicine and enzymes for catalysis.

Strain improvement for production of pharmaceuticals and other microbial metabolites by fermentation

Microbes have been good to us. They have given us thousands of valuable products with novel structures and activities. In nature, they only produce tiny amounts of these secondary metabolic products as a matter of survival. Thus, these metabolites are not overproduced in nature, but they must be overproduced in the pharmaceutical industry. Genetic manipulations are used in industry to obtain strains that produce hundreds or thousands of times more than that produced by the originally isolated strain. These strain improvement programs traditionally employ mutagenesis followed by screening or selection; this is known as 'brute-force' technology. Today, they are supplemented by modern strategic technologies developed via advances in molecular biology, recombinant DNA technology, and genetics. The progress in strain improvement has increased fermentation productivity and decreased costs tremendously. These genetic programs also serve other goals such as the elimination of undesirable products or analogs, discovery of new antibiotics, and deciphering of biosynthetic pathways.

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.

Hybrid antibiotics

Hybrid antibiotics that do not occur in nature have been obtained by combining structural genes of antibiotic producers. Some of these substances were effective against pathogenic microorganisms resistant against antibiotics produced by the parent strains. The majority of hybrid antibiotics were obtained by combining genes encoding polyketide synthases. Hybrid peptides with new biological properties have also been synthesized.

Deoxysugar Methylation during Biosynthesis of the Antitumor Polyketide Elloramycin by Streptomyces olivaceus

The anthracycline-like polyketide drug elloramycin is produced by Streptomyces olivaceus Tü2353. Elloramycin has antibacterial activity against Gram-positive bacteria and also exhibits antitumor activity. From a cosmid clone (cos16F4) containing part of the elloramycin biosynthesis gene cluster, three genes (elmMI, elmMII, and elmMIII) have been cloned. Sequence analysis and data base comparison showed that their deduced products resembled S-adenosylmethionine-dependent O-methyltransferases. The genes were individually expressed in Streptomyces albus and also coexpressed with genes involved in the biosynthesis of l-rhamnose, the 6-deoxysugar attached to the elloramycin aglycon. The resulting recombinant strains were used to biotransform three different elloramycin-type compounds: l-rhamnosyl-tetracenomycin C, l-olivosyl-tetracenomycin C, and l-oleandrosyl-tetracenomycin, which differ in their 2'-, 3'-, and 4'-substituents of the sugar moieties. When only the three methyltransferase-encoding genes elmMI, elmMII, and elmMIII were individually expressed in S. albus, the methylating activity of the three methyltransferases was also assayed in vitro using various externally added glycosylated substrates. From the combined results of all of these experiments, it is proposed that methyltransferases ElmMI, ElmMII, and ElmMIII are involved in the biosynthesis of the permethylated l-rhamnose moiety of elloramycin. ElmMI, ElmMII, and ElmMIII are responsible for the consecutive methylation of the hydroxy groups at the 2'-, 3'-, and 4'-position, respectively, after the sugar moiety has been attached to the aglycon.