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Comparative Genomics Reveals New Molecular targets for Accelerated Improvement of Erythromycin-producing Strains

ABSTRACT: Information about molecular mechanisms underlying improvement of antibiotic-producing microorganisms with traditional mutation and screening approach is largely missing. This information is essential to develop rational approaches to strain improvement. In this study by using comparative genomic analysis we have identified all genetic changes that have occurred during development of an erythromycin overproducer, which was obtained by the traditional mutate-and-screen method. Compared with parental Saccharopolyspora erythraea NRRL 2338, a total of 117 deletion, 78 insertion and 12 transposition sites were found across the genome of the overproducer. Among them, 71 insertion/deletion sites mapped within coding sequences (CDSs) generating frame-shift mutations. Moreover, single nucleotide variations affecting a total of 144 CDSs were identified between the two genomes. Overall, variations affect a total of 227 proteins in the genome of the overproducer. The analysis of metabolic pathways demonstrated that a considerable number of mutations affect genes coding for key enzymes involved in central carbon and nitrogen metabolism, and biosynthesis of secondary metabolites, redirecting common precursors toward erythromycin biosynthesis. Interestingly, several mutations inactivate genes coding for proteins that play fundamental roles in basic transcription and translation machineries including the transcription anti-termination factor NusB and the transcription elongation factor Efp. These mutations, along with those affecting genes coding for pleiotropic or pathway-specific regulators, may affect global expression profile. Consistent transcriptomic data were obtained from a comparative analysis between NRRL 2338 and the erythromycin overproducer gene expression profiling performed with DNA microarray. Genomic data also indicated that the mutate-and-screen process might have been accelerated by mutations in DNA repair genes. Our findings, largely unanticipated, reveal new targets suitable for rationale improvement of antibiotic-producing strains. According to a rough estimate, actinomycetes, which are among the most abundant bacteria in soil, produce over 70% of naturally occurring antibiotics and other biologically active substances including anti-tumour agents and immunosuppressants. However, these microorganisms must often be genetically improved for higher production before they can be used in the industry. Strain improvement has traditionally relied on multiple rounds of random mutagenesis and screening. This method is essentially empirical, and notably time-consuming and expansive. Currently, the availability of molecular genetics tools and useful information about the biosynthetic pathways and genetic control for most of biologically active substances has opened the way for improving strains by rational engineering. These rational strain improvement strategies benefit of the support of genomic and post-genomic technologies. In this study by using comparative genomic analysis we have identified all genetic changes that have occurred during development of an erythromycin overproducer, which was obtained by the traditional mutate-and-screen method. Our findings, largely unanticipated, reveal new molecular targets suitable for rationale improvement of antibiotic-producing strains by recombinant technologies, and support the evidence that combining classical and recombinant strain improvement with a solid fermentation development program is the best way to improve production of biologically active substances.

ORGANISM(S): Saccharopolyspora erythraea

PROVIDER: GSE30600 | GEO | 2012/05/24

SECONDARY ACCESSION(S): PRJNA144545

REPOSITORIES: GEO

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Project description:Information about molecular mechanisms underlying improvement of antibiotic-producing microorganisms with traditional mutation and screening approach is largely missing. This information is essential to develop rational approaches to strain improvement. In this study by using comparative genomic analysis we have identified all genetic changes that have occurred during development of an erythromycin overproducer, which was obtained by the traditional mutate-and-screen method. Compared with parental Saccharopolyspora erythraea NRRL 2338, a total of 117 deletion, 78 insertion and 12 transposition sites were found across the genome of the overproducer. Among them, 71 insertion/deletion sites mapped within coding sequences (CDSs) generating frame-shift mutations. Moreover, single nucleotide variations affecting a total of 144 CDSs were identified between the two genomes. Overall, variations affect a total of 227 proteins in the genome of the overproducer. The analysis of metabolic pathways demonstrated that a considerable number of mutations affect genes coding for key enzymes involved in central carbon and nitrogen metabolism, and biosynthesis of secondary metabolites, redirecting common precursors toward erythromycin biosynthesis. Interestingly, several mutations inactivate genes coding for proteins that play fundamental roles in basic transcription and translation machineries including the transcription anti-termination factor NusB and the transcription elongation factor Efp. These mutations, along with those affecting genes coding for pleiotropic or pathway-specific regulators, may affect global expression profile. Consistent transcriptomic data were obtained from a comparative analysis between NRRL 2338 and the erythromycin overproducer gene expression profiling performed with DNA microarray. Genomic data also indicated that the mutate-and-screen process might have been accelerated by mutations in DNA repair genes. Our findings, largely unanticipated, reveal new targets suitable for rationale improvement of antibiotic-producing strains. According to a rough estimate, actinomycetes, which are among the most abundant bacteria in soil, produce over 70% of naturally occurring antibiotics and other biologically active substances including anti-tumour agents and immunosuppressants. However, these microorganisms must often be genetically improved for higher production before they can be used in the industry. Strain improvement has traditionally relied on multiple rounds of random mutagenesis and screening. This method is essentially empirical, and notably time-consuming and expansive. Currently, the availability of molecular genetics tools and useful information about the biosynthetic pathways and genetic control for most of biologically active substances has opened the way for improving strains by rational engineering. These rational strain improvement strategies benefit of the support of genomic and post-genomic technologies. In this study by using comparative genomic analysis we have identified all genetic changes that have occurred during development of an erythromycin overproducer, which was obtained by the traditional mutate-and-screen method. Our findings, largely unanticipated, reveal new molecular targets suitable for rationale improvement of antibiotic-producing strains by recombinant technologies, and support the evidence that combining classical and recombinant strain improvement with a solid fermentation development program is the best way to improve production of biologically active substances. Erythromycin over-producing Strain at various time points

Project description:In the present study, we have used a genomic approach to understand how the classical mutate-and-screen method actually generated an improved rifamycin B producer. Compared with the reference strains Amycolatopsis mediterranei S699 (rifamycin B producer) and U32 (rifamycin SV producer), a total of 250 variations affecting a total of 227 coding sequences (CDS) were found in rifamycin B overproducing strain HP-130. One hundred nine CDS variations were specific to HP-130 as they were absent in both S699 and U32. A lot of variations affected genes coding for fatty acid (an lipid) metabolism, which is tightly interconnected with rifamycin biosynthesis by common metabolic precursors (malonyl-CoA, methylmalonyl-CoA). Interestingly, a nonsense mutation was mapped within mutB coding for methylmalonyl-CoA mutase suggesting the importance of metabolic re-direction of carbon flow toward rifamycin biosynthesis in the over-producing phenotype of HP-130. Other key mutations were: i.) a missense mutation affecting ppk, which encodes a polyphosphate kinase and was previously shown to play a negative role in the control of antibiotic biosynthesis in Streptomyces lividans; ii.) a missense mutation in argS2 affecting one of the two arginyl tRNA synthetases of A. mediterranei; iii.) a missense mutation in rifN coding for a protein belonging to the ROK family of transcriptional regulators with kanosamine kinase activity. Microarray analysis of the transcriptome of HP-130 as compared to that of S699 was useful to understand the effects of several mutations on global gene expression profile. Genomic and transcriptomic data were used to improve rifamycin B production in S699 by genetic engineering thus proving the causative effect of the above-mentioned mutations on the overproducing phenotype. In this study by using comparative genomic analysis we have identified all genetic changes that have occurred during development of a rifamycin B overproducer (HP-130), which was obtained by the traditional mutate-and-screen method. To gain insight about the mechanisms underlying improved rifamycin B production in HP-130, DNA microarray of A. mediterranei were manufactured and used for comparative analysis of the gene expression profile in HP-130 and S699. In DNA microarray experiments the two strains were cultivated under standard batch-culture conditions in modified RFB 2244 fermentation medium, and samples were collected at different time points (24-72 h) for RNA extraction. Gene expression data were analyzed to identify transcripts modulated during the growth curve. Amycolatopsis mediterranei S699 (WT) and the improved rifamycin B producer (HP-130) were profiled at 5 time points. For each time point two biological replicates are provided.

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Comparative Genomics Reveals New Molecular targets for Accelerated Improvement of Erythromycin-producing Strains

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