Overproduction of rifamycin B by Amycolatopsis mediterranei and its relationship with the toxic effect of barbital on growth

Continuous carbon source supply is essential for high rifamycin productivity of Amycolatopsis mediterranei in nitrate-stimulated fermentation revealed by a metabolomic study

Amycolatopsis mediterranei U32 is an industrial strain capable of producing therapeutically useful rifamycin SV. In early days of fermentation studies, nitrate was found to increase the yield of rifamycin along with globally, affecting both carbon and nitrogen metabolism in favor of antibiotic biosynthesis; thus, the nitrate-stimulating effect (NSE) hypothesis was proposed. Although GlnR is likely the master regulator of the pleotropic effect of NSE, the global metabolism affected by NSE has never been systematically examined. In this study, we use mass spectrometry-based metabolomics to quantitatively monitor the metabolomic responses of A. mediterranei U32 to nitrate supplementation. The concentrations of many metabolites involved in central carbon metabolism, including glucose 6-phosphate, glucose 1-phosphate, UDP-glucose, and acetyl-coenzyme A, decrease significantly after the addition of 80 mM potassium nitrate to the medium. We find that the rifamycin SV production yield could be increased by the addition of glucose during the logarithmic growth phase. Moreover, at multiple time points during glucose supplementation in the mid- and late-exponential phases, the yield of rifamycin SV further increases, reaching 354.3%. Quantitative real-time PCR assays of the key genes corresponding to the synthesis of the rifamycin SV precursor combined with data from metabolomics analysis confirm that carbon source deficiency is compensated for after glucose supplementation and that the expression of genes involved in the pathway of 3-amino-5-hydroxybenzoic acid synthesis by UDP-glucose and glutamine is significantly increased. This preliminary exploration of dynamic metabolomic profiles has the potential to increase our understanding of the NSE.

Identification of Antimicrobial Compounds in Two Streptomyces sp. Strains Isolated From Beehives

The World Health Organization warns that the alarming increase in antibiotic resistant bacteria will lead to 2.7 million deaths annually due to the lack of effective antibiotic therapies. Clearly, there is an urgent need for short-term alternatives that help to alleviate these alarming figures. In this respect, the scientific community is exploring neglected ecological niches from which the prototypical antibiotic-producing bacteria Streptomycetes are expected to be present. Recent studies have reported that honeybees and their products carry Streptomyces species that possess strong antibacterial activity. In this study, we have investigated the antibiotic profile of two Streptomycetes strains that were isolated from beehives. One of the isolates is the strain Streptomyces albus AN1, which derives from pollen, and shows potent antimicrobial activity against Candida albicans. The other isolate is the strain Streptomyces griseoaurantiacus AD2, which was isolated from honey, and displays a broad range of antimicrobial activity against different Gram-positive bacteria, including pathogens such as Staphylococcus aureus and Enterococus faecalis. Cultures of S. griseoaurantiacus AD2 have the capacity to produce the antibacterial compounds undecylprodigiosin and manumycin, while those of S. albus AN1 accumulate antifungal compounds such as candicidins and antimycins. Furthermore, genome and dereplication analyses suggest that the number of putative bioactive metabolites produced by AD2 and AN1 is considerably high, including compounds with anti-microbial and anti-cancer properties. Our results postulate that beehives are a promising source for the discovery of novel bioactive compounds that might be of interest to the agri-food sector and healthcare pharmaceuticals.

CRISPR-Cas12a-Assisted Genome Editing in Amycolatopsis mediterranei

Amycolatopsis mediterranei U32 is an industrial producer of rifamycin SV, whose derivatives have long been the first-line antimycobacterial drugs. In order to perform genetic modification in this important industrial strain, a lot of efforts have been made in the past decades and a homologous recombination-based method was successfully developed in our laboratory, which, however, requires the employment of an antibiotic resistance gene for positive selection and did not support convenient markerless gene deletion. Here in this study, the clustered regularly interspaced short palindromic repeat (CRISPR) system was employed to establish a genome editing system in A. mediterranei U32. Specifically, the Francisella tularensis subsp. novicida Cas12a (FnCas12a) gene was first integrated into the U32 genome to generate target-specific double-stranded DNA (dsDNA) breaks (DSBs) under the guidance of CRISPR RNAs (crRNAs). Then, the DSBs could be repaired by either the non-homologous DNA end-joining (NHEJ) system or the homology-directed repair (HDR) pathway, generating inaccurate or accurate mutations in target genes, respectively. Besides of A. mediterranei, the present work may also shed light on the development of CRISPR-assisted genome editing systems in other species of the Amycolatopsis genus.

GlnR Dominates Rifamycin Biosynthesis by Activating the rif Cluster Genes Transcription Both Directly and Indirectly in Amycolatopsis mediterranei

Because of the remarkable efficacy in treating mycobacterial infections, rifamycin and its derivatives are still first-line antimycobacterial drugs. It has been intensely studied to increase rifamycin yield from Amycolatopsis mediterranei, and nitrate is found to provide a stable and remarkable stimulating effect on the rifamycin production, a phenomenon known as "nitrate-stimulating effect (NSE)". Although the NSE has been widely used for the industrial production of rifamycin, its detailed molecular mechanism remains ill-defined. And our previous study has established that the global nitrogen regulator GlnR may participate in the NSE, but the underlying mechanism is still enigmatic. Here, we demonstrate that GlnR directly controls rifamycin biosynthesis in A. mediterranei and thus plays an essential role in the NSE. Firstly, GlnR specifically binds to the upstream region of rifZ, which leads us to uncover that rifZ has its own promoter. As RifZ is a pathway-specific activator for the whole rif cluster, GlnR indirectly upregulates the whole rif cluster transcription by directly activating the rifZ expression. Secondly, GlnR specifically binds to the upstream region of rifK, which is also characterized to have its own promoter. It is well-known that RifK is a 3-amino-5-hydroxybenzoic acid (AHBA, the starter unit of rifamycin) synthase, thus GlnR can promote the supply of the rifamycin precursor by directly activating the rifK transcription. Notably, GlnR and RifZ independently activate the rifK transcription through binding to different sites in rifK promoter region, which suggests that the cells have a sophisticated regulatory mechanism to control the AHBA biosynthesis. Collectively, this study reveals that GlnR activates the rif cluster transcription in both direct (for rifZ and rifK) and indirect (for the whole rif cluster) manners, which well interprets the phenomenon that the NSE doesn't occur in the glnR null mutant. Furthermore, this study deepens our understanding about the molecular mechanism of the NSE.

Gutierrez L, Reyes AG, Absalón AE, Kelly S. Improving rifamycin production in Amycolatopsis mediterranei by expressing a Vitreoscilla hemoglobin (vhb) gene fused to a cytochrome P450 monooxygenase domain

Expression of the vhb gene encoding hemoglobin from Vitreoscilla stercoraria in several organisms, clearly enhances oxygen-dependent product formation. In a previous work, we expressed the vhb gene that encodes hemoglobin from V. stercoraria in Amycolatopsis mediterranei, resulting in an increase (oxygen-dependent formation) in rifamycin B production. In the present work, we first confirm; by heterologous expression in Escherichia coli, that rif-orf5 from the rifamycin biosynthetic gene cluster, really encodes a cytochrome P450 enzyme, which is the key step for oxygen incorporation in the final biosynthetic product. Likewise, we fused rif-orf5 to the vhb gene, as part of a genetic engineering strategy. The fused genes were used to generate an Amycolatopsis mediterranei transformant (Msb-HbCYP5). Interestingly, the fermentation of Msb-HbCYP5 manifested 1.5-fold higher rifamicin B production than the transformant with only the hemoglobin gene, and 2.2-fold higher than the parental strain.

GlnR positive transcriptional regulation of the phosphate-specific transport system pstSCAB in Amycolatopsis mediterranei U32

Amycolatopsis mediterranei U32 is an important industrial strain for the production of rifamycin SV. Rifampicin, a derivative of rifamycin SV, is commonly used to treat mycobacterial infections. Although phosphate has long been known to affect rifamycin biosynthesis, phosphate transport, metabolism, and regulation are poorly understood in A. mediterranei. In this study, the functional phosphate transport system pstSCAB was isolated by RNA sequencing and inactivated by insertion mutation in A. mediterranei U32. The mycelium morphology changed from a filamentous shape in the wild-type and pstS1+ strains to irregular swollen shape at the end of filamentous in the ΔpstS1 strain. RT-PCR assay revealed that pstSCAB genes are co-transcribed as a polycistronic messenger. The pstSCAB transcription was significantly activated by nitrate supplementation and positively regulated by GlnR which is a global regulator of nitrogen metabolism in actinomycetes. At the same time, the yield of rifamycin SV decreased after mutation (ΔpstS1) compared with wild-type U32, which indicated a strong connection among phosphate metabolism, nitrogen metabolism, and rifamycin production in actinomycetes.

A feedback regulatory model for RifQ-mediated repression of rifamycin export in Amycolatopsis mediterranei

BACKGROUND

Due to the important role of rifamycin in curing tuberculosis infection, the study on rifamycin has never been stopped. Although RifZ, which locates within the rifamycin biosynthetic cluster, has recently been characterized as a pathway-specific regulator for rifamycin biosynthesis, little is known about the regulation of rifamycin export.

RESULTS

In this work, we proved that the expression of the rifamycin efflux pump (RifP) was regulated by RifQ, a TetR-family transcriptional regulator. Deletion of rifQ had little impact on bacterial growth, but resulted in improved rifamycin production, which was consistent with the reverse transcription PCR results that RifQ negatively regulated rifP's transcription. With electrophoretic mobility shift assay and DNase I Footprinting assay, RifQ was found to directly bind to the promoter region of rifP, and a typical inverted repeat was identified within the RifQ-protected sequences. The transcription initiation site of rifP was further characterized and found to be upstream of the RifQ binding sites, well explaining the RifQ-mediated repression of rifP's transcription in vivo. Moreover, rifamycin B (the end product of rifamycin biosynthesis) remarkably decreased the DNA binding affinity of RifQ, which led to derepression of rifamycin export, reducing the intracellular concentration of rifamycin B as well as its toxicity against the host.

CONCLUSIONS

Here, we proved that the export of rifamycin B was repressed by RifQ in Amycolatopsis mediterranei, and the RifQ-mediated repression could be specifically relieved by rifamycin B, the end product of rifamycin biosynthesis, based on which a feedback model was proposed for regulation of rifamycin export. With the findings here, one could improve the antibiotic yield by simply inactivating the negative regulator of the antibiotic transporter.

Conjugation of ϕBT1-derived integrative plasmid pDZL802 in Amycolatopsis mediterranei U32

The genus Amycolatopsis is well known for its ability to produce antibiotics, and an increasing number of valuable biotechnological applications, such as bioremediation, biodegradation, bioconversion, and potentially biofuel, that use this genus have been developed. Amycolatopsis mediterranei is an industrial-scale producer of the important antibiotic rifamycin, which plays a vital role in antimycobacterial therapy. Genetic studies of Amycolatopsis species have progressed slowly due to the lack of efficient transformation methods and stable plasmid vectors. In A. mediterranei U32, electroporation and replicable plasmid vectors have been developed. Here, we establish a simple and efficient conjugal system by transferring integrative plasmid pDZL802 from ET12567 (pUZ8002) to A. mediterranei U32, with an efficiency of 4 × 10^-5 CFU per recipient cell. This integrative vector, based on the ϕBT1 int-attP locus, is a stable and versatile tool for A. mediterranei U32, and it may also be applicable to various other Amycolatopsis species for strain improvement, heterologous protein expression, and synthetic biology experiments.

RifZ (AMED_0655) Is a Pathway-Specific Regulator for Rifamycin Biosynthesis in Amycolatopsis mediterranei

Rifamycin and its derivatives are particularly effective against the pathogenic mycobacteria Mycobacterium tuberculosis and Mycobacterium leprae Although the biosynthetic pathway of rifamycin has been extensively studied in Amycolatopsis mediterranei, little is known about the regulation in rifamycin biosynthesis. Here, an in vivo transposon system was employed to identify genes involved in the regulation of rifamycin production in A. mediterranei U32. In total, nine rifamycin-deficient mutants were isolated, among which three mutants had the transposon inserted in AMED_0655 (rifZ, encoding a LuxR family regulator). The rifZ gene was further knocked out via homologous recombination, and the transcription of genes in the rifamycin biosynthetic gene cluster (rif cluster) was remarkably reduced in the rifZ null mutant. Based on the cotranscription assay results, genes within the rif cluster were grouped into 10 operons, sharing six promoter regions. By use of electrophoretic mobility shift assay and DNase I footprinting assay, RifZ was proved to specially bind to all six promoter regions, which was consistent with the fact that RifZ regulated the transcription of the whole rif cluster. The binding consensus sequence was further characterized through alignment using the RifZ-protected DNA sequences. By use of bionformatic analysis, another five promoters containing the RifZ box (CTACC-N8-GGATG) were identified, among which the binding of RifZ to the promoter regions of both rifK and orf18 (AMED_0645) was further verified. As RifZ directly regulates the transcription of all operons within the rif cluster, we propose that RifZ is a pathway-specific regulator for the rif cluster.IMPORTANCE To this day, rifamycin and its derivatives are still the first-line antituberculosis drugs. The biosynthesis of rifamycin has been extensively studied, and most biosynthetic processes have been characterized. However, little is known about the regulation of the transcription of the rifamycin biosynthetic gene cluster (rif cluster), and no regulator has been characterized. Through the employment of transposon screening, we here characterized a LuxR family regulator, RifZ, as a direct transcriptional activator for the rif cluster. As RifZ directly regulates the transcription of the entire rif cluster, it is considered a pathway-specific regulator for rifamycin biosynthesis. Therefore, as the first regulator characterized for direct regulation of rif cluster transcription, RifZ may provide a new clue for further engineering of high-yield industrial strains.

A preliminary study of the mechanism of nitrate-stimulated remarkable increase of rifamycin production in Amycolatopsis mediterranei U32 by RNA-seq

BACKGROUND

Rifamycin is an important antibiotic for the treatment of infectious disease caused by Mycobacteria tuberculosis. It was found that in Amycolatopsis mediterranei U32, an industrial producer for rifamycin SV, supplementation of nitrate into the medium remarkably stimulated the yield of rifamycin SV. However, the molecular mechanism of this nitrate-mediated stimulation remains unknown.

RESULTS

In this study, RNA-sequencing (RNA-seq) technology was employed for investigation of the genome-wide differential gene expression in U32 cultured with or without nitrate supplementation. In the presence of nitrate, U32 maintained a high transcriptional level of genes both located in the rifamycin biosynthetic cluster and involved in the biosynthesis of rifamycin precursors, including 3-amino-5-dihydroxybenzoic acid, malonyl-CoA and (S)-methylmalonyl-CoA. However, when nitrate was omitted from the medium, the transcription of these genes declined sharply during the transition from the mid-logarithmic phase to the early stationary phase. With these understandings, one may easily propose that nitrate stimulates the rifamycin SV production through increasing both the precursors supply and the enzymes for rifamycin biosynthesis.

CONCLUSION

It is the first time to thoroughly illustrate the mechanism of the nitrate-mediated stimulation of rifamycin production at the transcriptional level, which may facilitate improvement of the industrial production of rifamycin SV, e.g. through optimizing the global rifamycin biosynthetic pathways on the basis of RNA-seq data.

Improved Rifamycin B Production by Nocardia mediterranei MTCC 14 under Solid-State Fermentation through Process Optimization

Optimization of various production parameters using response surface methodology (RSM) was performed to assess maximum yield of rifamycin B from Nocardia mediterranei MTCC 14. Plackett-Burman design test was applied to determine the significant effects of various production parameters such as glucose, maltose, ribose, galactose, beef extract, peanut meal, ammonium chloride, ammonium sulphate, barbital, pH, and moisture content on production of rifamycin B. Among the eleven variables tested, galactose, ribose, glucose, and pH were found to have significant effect on rifamycin B production. Optimum levels of the significant variables were decided by using a central composite design. The most appropriate condition for production of rifamycin B was found to be a single step production at galactose (8% w/w), ribose (3% w/w), glucose (9% w/w), and pH (7.0). At these optimum production parameters, the maximum yield of rifamycin B obtained experimentally (9.87 g/kgds dry sunflower oil cake) was found to be very close to its predicted value of 10.35 g/kgds dry sunflower oil cake. The mathematical model developed was found to fit greatly with the experimental data of rifamycin B production.

GlnR negatively regulates the transcription of the alanine dehydrogenase encoding gene ald in Amycolatopsis mediterranei U32 under nitrogen limited conditions via specific binding to its major transcription initiation site

Ammonium assimilation is catalyzed by two enzymatic pathways, i.e., glutamine synthetase/glutamate synthase (GS/GOGAT) and alanine dehydrogenase (AlaDH) in Amycolatopsis mediterranei U32. Under nitrogen-rich conditions, the AlaDH pathway is the major route for ammonium assimilation, while the GS/GOGAT pathway takes over when the extracellular nitrogen supply is limited. The global nitrogen regulator GlnR was previously characterized to activate the transcription of the GS encoding gene glnA in response to nitrogen limitation and is demonstrated in this study as a repressor for the transcription of the AlaDH encoding gene ald, whose regulation is consistent with the switch of the ammonium assimilation pathways from AlaDH to GS/GOGAT responding to nitrogen limitation. Three transcription initiation sites (TISs) of ald were determined with primer extension assay, among which transcription from aldP2 contributed the major transcripts under nitrogen-rich conditions but was repressed to an undetectable level in response to nitrogen limitation. Through DNase I footprinting assay, two separate regions were found to be protected by GlnR within ald promoter, within which three GlnR binding sites (a1, b1 sites in region I and a2 site in region II) were defined. Interestingly, the major TIS aldP2 is located in the middle of a2 site within region II. Therefore, one may easily conclude that GlnR represses the transcription of ald via specific binding to the GlnR binding sites, which obviously blocks the transcription initiation from aldP2 and therefore reduces ald transcripts.

Atypical OmpR/PhoB subfamily response regulator GlnR of actinomycetes functions as a homodimer, stabilized by the unphosphorylated conserved Asp-focused charge interactions

The OmpR/PhoB subfamily protein GlnR of actinomycetes is an orphan response regulator that globally coordinates the expression of genes related to nitrogen metabolism. Biochemical and genetic analyses reveal that the functional GlnR from Amycolatopsis mediterranei is unphosphorylated at the potential phosphorylation Asp(50) residue in the N-terminal receiver domain. The crystal structure of this receiver domain demonstrates that it forms a homodimer through the α4-β5-α5 dimer interface highly similar to the phosphorylated typical response regulator, whereas the so-called "phosphorylation pocket" is not conserved, with its space being occupied by an Arg(52) from the β3-α3 loop. Both in vitro and in vivo experiments confirm that GlnR forms a functional homodimer via its receiver domain and suggest that the charge interactions of Asp(50) with the highly conserved Arg(52) and Thr(9) in the receiver domain may be crucial in maintaining the proper conformation for homodimerization, as also supported by molecular dynamics simulations of the wild type GlnR versus the deficient mutant GlnR(D50A). This model is backed by the distinct phenotypes of the total deficient GlnR(R52A/T9A) double mutant versus the single mutants of GlnR (i.e. D50N, D50E, R52A and T9A), which have only minor effects upon both dimerization and physiological function of GlnR in vivo, albeit their DNA binding ability is weakened compared with that of the wild type. By integrating the supportive data of GlnRs from the model Streptomyces coelicolor and the pathogenic Mycobacterium tuberculosis, we conclude that the actinomycete GlnR is atypical with respect to its unphosphorylated conserved Asp residue being involved in the critical Arg/Asp/Thr charge interactions, which is essential for maintaining the biologically active homodimer conformation.

Three of four GlnR binding sites are essential for GlnR-mediated activation of transcription of the Amycolatopsis mediterranei nas operon

In Amycolatopsis mediterranei U32, genes responsible for nitrate assimilation formed one operon, nasACKBDEF, whose transcription is induced by the addition of nitrate. Here, we characterized GlnR as a direct transcriptional activator for the nas operon. The GlnR-protected DNA sequences in the promoter region of the nas operon were characterized by DNase I footprinting assay, the previously deduced Streptomyces coelicolor double 22-bp GlnR binding consensus sequences comprising a1, b1, a2, and b2 sites were identified, and the sites were then mutated individually to test their roles in both the binding of GlnR in vitro and the GlnR-mediated transcriptional activation in vivo. The results clearly showed that only three GlnR binding sites (a1, b1, and b2 sites) were required by GlnR for its specific binding to the nas promoter region and efficient activation of the transcription of the nas operon in U32, while the a2 site seemed unnecessary.

Identification and functional analysis of a nitrate assimilation operon nasACKBDEF from Amycolatopsis mediterranei U32

Nitrate assimilation has been well studied for Gram-negative bacteria but not so much in the Gram-positive actinomycetes up to date. In a rifamycin SV-producing actinomycete, Amycolatopsis mediterranei strain U32, nitrate not only can be used as a sole nitrogen source but also remarkably stimulates the antibiotic production along with regulating the related metabolic enzymes. A gene cluster of nasACKBDEF was cloned from a U32 genomic library by in situ hybridization screening with a heterogeneous nasB probe and confirmed later by whole genome sequence, corresponding to the protein coding genes of AMED_1121 to AMED_1127. These genes were co-transcribed as an operon, concomitantly repressed by ammonium while activated with supplement of either nitrate or nitrite. Genetic and biochemical analyses identified the essential nitrate/nitrite assimilation functions of the encoded proteins, orderly, the assimilatory nitrate reductase catalytic subunit (NasA), nitrate reductase electron transfer subunit (NasC), nitrate/nitrite transporter (NasK), assimilatory nitrite reductase large subunit (NasB) and small subunit (NasD), bifunctional uroporphyrinogen-III synthase (NasE), and an unknown function protein (NasF). Comparing rifamycin SV production and the level of transcription of nasB and rifE from U32 and its individual nas mutants in Bennet medium with or without nitrate indicated that nitrate assimilation function encoded by the nas operon played an essential role in the "nitrate stimulated" rifamycin production but had no effect upon the transcription regulation of the primary and secondary metabolic genes related to rifamycin biosynthesis.

Development of balanced medium composition for improved rifamycin B production by isolated Amycolatopsis sp. RSP-3

AIM

To develop optimum fermentation environment for enhanced rifamycin B production by isolated Amycolatopsis sp. RSP-3.

METHODS AND RESULTS

The impact of different fermentation parameters on rifamycin B production by isolated Amycolatopsis sp. RSP-3 was investigated using Taguchi methodology. Controlling fermentation factors were selected based on one variable at a time methodology. The isolated strain revealed more than 25% higher production compared to literature reports. Five different nutritional components (soyabean meal, glucose, potassium nitrate, calcium carbonate and barbital) and inoculum concentration showed impact on rifamycin B production at individual and interactive level. At optimized environment, 65% contribution was observed from selected fermentation parameters.

CONCLUSIONS

Soyabean meal and calcium carbonate were the most significant factors among the selected factors followed by barbital and potassium nitrate. Glucose, however, showed the least significance on rifamycin B production with this strain. A maximum of 5.12 g l(-1) rifamycin B production was achieved with optimized medium containing (g l(-1)) soyabean meal, 27; glucose, 100; potassium nitrate, 4; calcium carbonate, 3 and barbital, 1.2.

SIGNIFICANCE AND IMPACT OF THE STUDY

The present study signifies identification of balanced medium component concentrations for improved rifamycin B production by isolated Amycolatopsis sp. RSP-3. This strain requires organic and inorganic nitrogen sources for effective product yield. Yet at individual level, organic nitrogen source has c. nine-fold higher influence compared to inorganic one.

RifP; a membrane protein involved in rifamycin export in Amycolatopsis mediterranei

The rifamycin gene cluster in Amycolatopsis mediterranei includes the gene rifP, whose role in antibiotic production has not yet been established. In this work, the rifP gene was silenced and the results indicated that it codes for a protein to export rifamycin, avoiding its accumulation inside the cell. An antisense cassette was constructed by inserting the rifP gene in an antisense orientation downstream from the modified ermE* promoter, and upstream of the Tasd terminator (aspartate semialdehyde dehydrogenase of A. lactamdurans). Partial silencing of the rifP gene by the use of the antisense cassette, cloned in the plasmid pUAMAE5, resulted in a 70% decrease in the extracellular rifamycin B. A protein of 53 kDa was absent in the membrane fraction of the silenced strain. This is the same size of the expected product from the rifP gene. The 2D structure analysis indicated it belongs to a Drug:H+ antiporter family which includes a wide number of membrane transport proteins.

Bacterial type I glutamine synthetase of the rifamycin SV producing actinomycete, Amycolatopsis mediterranei U32, is the only enzyme responsible for glutamine synthesis under physiological conditions

The structural gene for glutamine synthetase, glnA, from Amycolatopsis mediterranei U32 was cloned via screening a genomic library using the analog gene from Streptomyces coelicolor. The clone was functionally verified by complementing for glutamine requirement of an Escherichia coli glnA null mutant under the control of a lac promoter. Sequence analysis showed an open reading frame encoding a protein of 466 amino acid residues. The deduced amino acid sequence bears significant homologies to other bacterial type I glutamine synthetases, specifically, 71% and 72% identical to the enzymes of S. coelicolor and Mycobacterium tuberculosis, respectively. Disruption of this glnA gene in A. mediterranei U32 led to glutamine auxotrophy with no detectable glutamine synthetase activity in vivo. In contrast, the cloned glnA gene can complement for both phenotypes in trans. It thus suggested that in A. mediterranei U32, the glnA gene encoding glutamine synthetase is uniquely responsible for in vivo glutamine synthesis under our laboratory defined physiological conditions.

Replication and inheritance ofNocardiaplasmid pC1

Nocardia sp. C-14-1, isolated from acrylic fiber wastewater, can degrade long-chain alkanes and succinonitrile efficiently. Here we report the characterization of an indigenous plasmid pC1. The overall nucleotide sequence of pC1 consisted of 5841 bp. The five ORFs, encoding a DNA recombinase, replication protein (Rep(pC1)) and three proteins of unknown function, were predicted on pC1. The Rep(pC1) displayed its homology with the Rep of Rhodococcus large plasmid p33701, suggesting a theta type of replication. An Escherichia coli plasmid (containing the single rep(pC1) gene) propagated autonomously in low copy number in Nocardia or Rhodococcus, suggesting that rep(pC1) was an essential gene for plasmid replication. The plasmid (containing the single rep(pC1) gene) presented as inheritance unstable hints that other pC1 loci were required for the stable inheritance of plasmids. By comparison of the plasmid-borne Rep proteins, we classify Rhodococcus or Nocardia plasmids into four groups.

Cloning and characterization of the chromosomal replication origin region of Amycolatopsis mediterranei U32

The chromosomal replication origins (oriC) of gram positive, acid-fast actinomycetes have been investigated in streptomycetes and mycobacteria. A 1339 bp DNA fragment of the putative oriC region from the rifamycin SV producer Amycolatopsis mediterranei U32 was cloned by PCR amplification employing primers designed based on the conserved flanking genes of dnaA and dnaN. The 884 bp sequence of the intergenic region between dnaA and dnaN genes consists of 19 DnaA-boxes and two 13-mer AT-rich sequences, which is similar to the oriC structure of Streptomyces lividans. A mini-chromosome constructed by cloning the putative U32 oriC DNA fragment into an Escherichia coli plasmid was able to replicate autonomously, but was unstable, in A. mediterranei U32 with an estimated copy number of two per cell. Although efficient replication of the mini-chromosome in U32 requires the complete set of DnaA-boxes and AT-rich regions, only one of the AT-rich sequences together with part of the DnaA-boxes is sufficient, suggesting the presence of combinatorial alternatives for a functional oriC region of A. mediterranei U32. Phylogenetic analysis based on definite oriC sequences among eubacteria reflects well the relationship between these species.

Vector systems allowing efficient autonomous or integrative gene cloning in Micromonospora sp. strain 40027

Vector systems allowing autonomous or site-specific integrative gene cloning were developed for Micromonospora sp. strain 40027, a producer of the antibiotic fortimicin A. The autonomous system depends on the discovery of a low-copy-number, self-transmissible covalently closed circular plasmid, pJTU112 (ca. 14.1 kb), which was shown to be present in the progenitor strain in both integrated and autonomous states. The copy numbers of both wild-type pJTU112 and three derivatives of it can be amplified at least sixfold by addition of streptomycin to the culture medium. The integrative system was developed by the use of a pBR322-derived Escherichia coli plasmid vector, pSET152, mediated by the attP site of the Streptomyces phage PhiC31. Both vectors can be transferred by conjugation from E. coli into Micromonospora sp. strain 40027. The heterologous cloning and expression of the dnd gene cluster originating from Streptomyces lividans 1326 into Micromonospora sp. strain 40027 demonstrated the use of the two systems.

Biochemical mechanism of the effect of barbital on rifamycin B biosynthesis by Amycolatopsis mediterranei (M18 strain)

It is well known that 5,5-diethylbarbituric acid (barbital) in the culture medium can stimulate the production of rifamycin B by Amycolatopsis mediterranei, particularly in industrial processes. However, the mechanism by which barbital exerts this effect is unknown. Results in this work show that the barbital effect is only evident under low aeration conditions (50-ml microfermentors with 7 ml of medium, 0.08 l/h air flow). Under these conditions, cultures with barbital showed similar CO2 production (in relation to a control without barbital), but higher oxygen uptake indicated that the extra O2 consumed was used in the increased rifamycin biosynthesis. Moreover, using a resting cell system where no antibiotic is produced, it was possible to show that barbital inhibits the respiratory chain, since O2 uptake decreased by 30%. Finally, we present biochemical results that suggest that a cytochrome P450-type monoxygenase, which can use atmospheric oxygen, is induced by barbital in an industrial-type strain of A. mediterranei.

Efficient isolation of total RNA from antibiotic-producing bacterium Amycolatopsis mediterranei

RNA extraction from antibiotic-producing actinomycetes can be a difficult and time-consuming process due to their special peptidoglycans cell wall composition and the short life of RNA. Hence, the rapidity of cellular lysis and complete inhibition of RNase are of particular importance for isolating intact RNA of high quality. The genus of Amycolatopsis mediterranei produces many clinically important antibiotics, such as rifamycin and vancomycin; however, the available methods for bacterial RNA isolation did not work very well with this genus. In this report, we described a new method for RNA isolation using the combination of LiCl, urea and guanidinium thiocyanate to disrupt the cell wall of Amycolatopsis. Compared with earlier published RNA isolation methods, the method gave higher yields of pure and intact RNA. About 1 microg total RNA free of DNA contamination can be obtained from 1 mg wet weight of A. mediterranei. The integrity of the RNA was demonstrated by formaldehyde agarose gel electrophoresis and Northern blot analyses.

Effect of uracil on rifamycin SV production by Amycolatopsis mediterranei MV35R

The effect of different organic nitrogen compounds on the production of rifamycin SV by Amycolatopsis mediterranei MV35R and their optimum concentrations have been described. Results obtained indicate that rifamycin SV production increased from 4020 mg l-1 to 4575 mg l-1 when organic nitrogen compound uracil was added at 0.2% (w/v) concentration to the fermentation medium by A. mediterranei MV35R. The rifamycin SV yield was enhanced by 505 mg l-1 using uracil (2 g l-1) when compared with barbital.