Enzyme Systems Involved in Antibiotic Synthesis

Abstract

Antibiotic synthesis is a complex biochemical process regulated by specialized enzyme systems. These include Non-Ribosomal Peptide Synthetases (NRPSs), Polyketide Synthases (PKSs), and hybrid NRPS-PKS systems, each orchestrating the stepwise assembly of bioactive compounds. These multifunctional enzyme complexes catalyze the formation of structurally diverse antibiotics such as penicillins, tetracyclines, erythromycin, and vancomycin. Recent advances in genome mining and synthetic biology have deepened our understanding of these enzymatic pathways, enabling the rational design of novel antibiotics. This review outlines the molecular mechanisms of the principal enzyme systems involved in antibiotic biosynthesis, focusing on their structure, function, and biotechnological applications.

Keywords:Antibiotic biosynthesis, Non-ribosomal peptide synthetase, Polyketide synthase, Enzyme systems, Natural products, Secondary metabolism

Introduction

The discovery of antibiotics revolutionized medicine, yet the rising threat of antimicrobial resistance demands the continuous search for new antimicrobial compounds. Most clinically important antibiotics are derived from natural sources, particularly filamentous bacteria such as Streptomyces and fungi like Penicillium. The biosynthesis of these complex molecules is mediated by sophisticated enzyme systems that coordinate the sequential transformation of simple precursors into pharmacologically active compounds [1]. Understanding the enzymatic machinery behind antibiotic synthesis is crucial for bioengineering novel antibiotics and enhancing yield in industrial fermentation.

The discovery of antibiotics marked a pivotal milestone in medical history, drastically reducing mortality from bacterial infections and enabling the advancement of modern clinical procedures such as surgery, chemotherapy, and organ transplantation. However, the escalating threat of Antimicrobial Resistance (AMR) has placed unprecedented pressure on the scientific community to discover and develop new antimicrobial agents. This challenge is compounded by the fact that the rate of new antibiotic discovery has declined since the golden age of antibiotic research in the mid-20thcentury [1].

A significant proportion of clinically important antibiotics are derived from natural sources, particularly filamentous bacteria of the genus Streptomyces and various fungal species, including Penicillium and Cephalosporium. These microorganisms inhabit diverse ecological niches, particularly soil environments, where interspecies competition has driven the evolution of complex secondary metabolic capabilities. As a result, these organisms have become prolific producers of structurally diverse and biologically potent compounds, many of which function as antibiotics [2].

The biosynthesis of antibiotics in these organisms is orchestrated by elaborate enzymatic systems encoded within Biosynthetic Gene Clusters (BGCs). These clusters encompass genes for core biosynthetic enzymes, regulatory proteins, resistance factors, and enzymes responsible for post-synthetic modifications. The core biosynthetic machinery often involves modular megasynthases such as Polyketide Synthases (PKSs) and Non-Ribosomal Peptide Synthetases (NRPSs), which operate in a highly organized, assembly- line fashion to construct the molecular scaffolds of antibiotics from simple acyl-CoA or amino acid building blocks [3].

In Streptomyces species, for instance, type I PKSs are responsible for the production of macrolide antibiotics such as erythromycin. These enzymes consist of multiple modules, each containing catalytic domains like Ketosynthase (KS), Acyltransferase (AT), and Acyl Carrier Protein (ACP), along with optional modifying domains such as Ketoreductase (KR), Dehydratase (DH), and Enoylreductase (ER). The sequential action of these modules results in the elongation and modification of polyketide chains, ultimately yielding structurally complex antibiotics [4].

Similarly, NRPSs catalyze the synthesis of non-ribosomal peptides such as vancomycin and daptomycin, which exhibit potent antibacterial activity. Each NRPS module incorporates one specific amino acid through a combination of Adenylation (A), Thiolation (T), and Condensation (C) domains. These systems can also incorporate non-proteinogenic amino acids, D-isomers, or chemically modified residues, contributing to the high degree of structural and functional diversity of peptide antibiotics [5].

Tailoring enzymes play a pivotal role in refining the pharmacological properties of antibiotic molecules. Glycosyltransferases, methyltransferases, oxidoreductases, and halogenases introduce site-specific modifications such as glycosylation, methylation, oxidation, and halogenation. These alterations enhance the solubility, stability, and bioactivity of the core antibiotic scaffold and can significantly influence its spectrum of antimicrobial activity [6].

In fungi, β-lactam antibiotics like penicillin and cephalosporin are synthesized through a distinct biosynthetic route. The key step in penicillin biosynthesis involves the formation of the tripeptide δ-(L-α-Aminoadipyl)-L-Cysteinyl-D-Valine (ACV) by the NRPS enzyme ACV synthetase. This intermediate is subsequently cyclized by isopenicillin N synthase, forming the characteristic β-lactam ring. Additional steps, including acylation and oxidation, convert isopenicillin N into bioactive penicillins or cephalosporins with varying side chains and pharmacological properties [7].

Understanding these biosynthetic systems has far-reaching implications for antibiotic discovery and development. Genetic and enzymatic manipulation of biosynthetic pathways enables the production of “unnatural natural products”-structural analogs of known antibiotics with improved activity or resistance profiles. Additionally, advances in synthetic biology and metabolic engineering have facilitated the heterologous expression of BGCs in amenable microbial hosts, allowing for the scalable production of novel antibiotics that were previously inaccessible [8].

Thus, detailed knowledge of the enzyme systems involved in antibiotic biosynthesis not only enhances our understanding of microbial metabolism but also provides powerful tools for addressing the global health crisis posed by antimicrobial resistance.

Among the most remarkable enzymatic systems involved in antibiotic biosynthesis are Non-Ribosomal Peptide Synthetases (NRPSs), which are large, multifunctional enzymes responsible for the assembly of a diverse array of bioactive peptide antibiotics. In contrast to conventional protein synthesis, NRPS-mediated peptide assembly occurs independently of the ribosome and is not constrained by the standard genetic code. This allows NRPSs to incorporate both proteinogenic and non-proteinogenic amino acids- including D-isomers, β-amino acids, hydroxy acids, and other chemically modified substrates-into structurally complex and pharmacologically potent molecules such as vancomycin, daptomycin, tyrocidine, and bacitracin [5].

These enzymatic complexes function in a modular fashion, with each module corresponding to the incorporation of a single amino acid residue. A canonical NRPS module comprises three essential catalytic domains. The Adenylation (A) domain is responsible for the specific recognition and activation of an amino acid substrate. It catalyzes the ATP-dependent conversion of the amino acid into an aminoacyl-adenylate intermediate, which is then transferred to the adjacent Thiolation (T) domain. Also known as the Peptidyl Carrier Protein (PCP), the T domain covalently binds the activated amino acid via a phosphopantetheine arm. The Condensation (C) domain subsequently catalyzes peptide bond formation between adjacent amino acid residues, facilitating the stepwise elongation of the peptide chain [9,10].

In addition to these core domains, many NRPS modules contain accessory domains that introduce critical chemical modifications to the growing peptide chain. Epimerization (E) domains convert L-amino acids into their D-isomeric forms, a feature often associated with enhanced resistance to proteolytic degradation and increased bioactivity. Methylation (M) domains catalyze N- or O-methylation reactions, while Cyclization (Cy) domains facilitate the formation of thiazole, oxazole, or other heterocyclic ring structures that contribute to the rigidity and functional specificity of the final product. These structural refinements are frequently essential for antibiotic activity [11].

Upon completion of peptide assembly, the product is typically released from the NRPS complex by a terminal Thioesterase (TE) domain, which catalyzes either hydrolytic cleavage or macrocyclization, depending on the structural demands of the antibiotic. The precise control of this release step is crucial for determining the final conformation and activity of the synthesized compound [12].

NRPS biosynthetic gene clusters are usually organized into operons and often encode additional tailoring enzymes that carry out post-synthetic modifications. These include hydroxylases, glycosyltransferases, halogenases, and acyltransferases, which can dramatically influence the solubility, membrane permeability, and target specificity of the antibiotic molecule. For example, glycosylation of vancomycin-related compounds plays a crucial role in improving their pharmacokinetics and reducing toxicity [13].

The tightly regulated expression of NRPS gene clusters ensures that energy-intensive peptide synthesis occurs only under appropriate environmental conditions. Regulatory genes encoded within or adjacent to the operons typically respond to nutrient availability, population density, or interspecies competition. Understanding the regulatory logic and enzymatic architecture of NRPSs has enabled synthetic biologists to design hybrid pathways and generate novel “non-natural” peptide antibiotics with customized properties by swapping or engineering individual modules and domains [14].

Taken together, NRPSs represent a versatile and highly programmable platform for the biosynthesis of complex peptide antibiotics. Their modularity and catalytic precision allow the generation of structurally diverse molecules with remarkable biological activities. Deciphering and manipulating these systems remain at the forefront of antibiotic discovery and synthetic biology.

Another major class of enzyme systems involved in the biosynthesis of antibiotics is the Polyketide Synthases (PKSs), which are responsible for generating a broad spectrum of structurally diverse and clinically valuable polyketide antibiotics, including erythromycin, tetracycline, chloramphenicol, and rifamycin. These multifunctional enzymes catalyze the sequential condensation of simple acyl- CoA-derived building blocks, typically acetyl-CoA and malonyl-CoA, into complex polyketide backbones. While the enzymology of PKSs shares mechanistic similarities with Fatty Acid Synthases (FASs), PKSs exhibit far greater structural diversity due to their ability to accommodate a wider range of substrates and to incorporate varied reduction, cyclization, and methylation steps into their biosynthetic programs [15].

Polyketide synthases are categorized into three main types based on their structural organization and catalytic mechanism. Type I PKSs are large, multifunctional polypeptides composed of multiple enzymatic modules, each responsible for a single round of polyketide chain elongation. Each module typically contains a Ketosynthase (KS) domain that catalyzes carbon–carbon bond formation, an Acyltransferase (AT) domain that selects and loads specific acyl-CoA substrates, and an Acyl Carrier Protein (ACP) domain that tethers the growing intermediate through a covalent phosphopantetheinyl arm. Additional domains such as Ketoreductase (KR), Dehydratase (DH), and Enoylreductase (ER) may be present to modify β-keto intermediates through a process of controlled reduction, dehydration, and full saturation, ultimately influencing the oxidation state and functionalization pattern of the final molecule. Erythromycin, a macrolide antibiotic produced by Saccharopolyspora erythraea, is a prototypical product of the modular Type I PKS system, known as the 6-Deoxyerythronolide B Synthase (DEBS) [4,16].

In contrast, Type II PKSs operate as dissociated multienzyme complexes rather than as a single polypeptide. These enzymes rely on a minimal set of catalytic components that act iteratively to elongate the polyketide chain. The minimal complex typically includes a discrete KS-CLF (chain length factor) heterodimer, a stand-alone ACP, and accessory enzymes that control cyclization and aromatization of the polyketide scaffold. Tetracycline and actinorhodin are classic examples of aromatic polyketides synthesized by Type II PKS systems found in Streptomyces species [17]. Despite the simplicity of their catalytic cores, Type II systems are capable of generating highly complex, polycyclic compounds, largely due to post-synthetic tailoring steps involving oxidases, methyltransferases, and glycosyltransferases.

Type III PKSs, also known as chalcone synthase-like enzymes, represent the simplest of the PKS families. These enzymes function as homodimeric proteins that catalyze multiple rounds of Claisenlike condensation reactions directly on acyl-CoA substrates without the use of ACPs. They are primarily found in plants but also occur in some bacterial species and contribute to the biosynthesis of small polyketides and flavonoid precursors. Unlike Type I and II systems, Type III PKSs do not rely on modular architecture but instead achieve product diversity through substrate selection and spontaneous cyclization events [18].

The domain architecture and programming logic of PKSs are pivotal determinants of the chemical structure and bioactivity of the resulting polyketide. Variations in the order, specificity, and activity of individual domains and modules can produce a vast range of chemical scaffolds, making these enzymes ideal platforms for rational engineering. For instance, swapping AT domains or modifying substrate specificity loops within KS domains has been shown to redirect biosynthetic pathways toward novel antibiotics with improved pharmacological profiles [19]. Advances in bioinformatics, synthetic biology, and combinatorial biosynthesis have further expanded the potential to exploit PKS systems for the production of next-generation antimicrobials, especially in the face of rising resistance to conventional therapies.

Several clinically important antibiotics, such as rapamycin, rifamycin, and bleomycin, are biosynthesized through hybrid enzyme systems that integrate both Non-Ribosomal Peptide Synthetases (NRPSs) and Polyketide Synthases (PKSs). These hybrid biosynthetic pathways combine the catalytic capabilities of both systems, allowing for the assembly of structurally complex and highly bioactive compounds by incorporating both amino acid-derived and polyketide-derived building blocks into a single molecular framework. This convergence of biosynthetic logics results in antibiotics with unique mechanisms of action and enhanced pharmacological profiles [20].

These hybrid systems are encoded within large gene clusters organized into alternating NRPS and PKS modules, each responsible for the activation, extension, and modification of specific molecular units. The coordination of these enzymatic modules is tightly regulated to ensure the fidelity of biosynthetic steps and the structural integrity of the final antibiotic molecule. In the case of bleomycin, for instance, the polyketide portion is synthesized by a PKS module and subsequently joined to the peptidic moiety via NRPS modules, resulting in a glycopeptide molecule capable of cleaving DNA strands through oxidative mechanisms [21].

Similarly, the biosynthesis of rifamycin involves a hybrid pathway where polyketide intermediates are extended and modified by NRPS enzymes, producing a potent inhibitor of bacterial RNA polymerase [22].

One of the major advantages of hybrid NRPS-PKS pathways lies in their modular architecture, which makes them amenable to genetic engineering. Advances in synthetic biology and molecular genetics have enabled researchers to recombine or redesign modules from different biosynthetic clusters to create “unnatural” natural products-novel antibiotics with enhanced spectrum, stability, or pharmacokinetics. For example, targeted modifications of PKSNRPS interfaces have successfully generated rapamycin analogues with improved binding affinity to mTOR complexes, expanding their utility beyond immunosuppression into oncology [4].

Furthermore, studies on the evolutionary plasticity of these clusters reveal that nature frequently employs module-swapping and gene duplication events to evolve new compounds. Understanding these evolutionary principles enables rational design of biosynthetic pathways and facilitates the generation of diverse chemical libraries. Such libraries are particularly valuable in combating the global challenge of antimicrobial resistance, where structurally novel antibiotics are urgently needed.

In summary, hybrid NRPS-PKS systems exemplify the remarkable biosynthetic potential of microbial secondary metabolism. Their ability to generate structurally diverse and pharmacologically potent molecules underscores their value in antibiotic discovery and development. Ongoing efforts to decode, manipulate, and reprogram these pathways offer promising avenues for the creation of next-generation therapeutics against multidrug-resistant pathogens.

The biosynthesis of antibiotics is not solely governed by core synthetases such as NRPSs and PKSs; rather, it requires the concerted action of various regulatory and tailoring enzymes that ensure the structural maturation, bioactivity, and self-protection of the producing organism. These auxiliary components play crucial roles in modulating gene expression, enzymatic specificity, and final structural modifications of the antibiotic molecules.

A central component of biosynthetic regulation involves transcriptional regulators that are responsive to environmental and intracellular signals. These include global regulatory proteins, sigma factors, and pathway-specific transcriptional activators or repressors. For instance, many actinomycetes regulate antibiotic Biosynthetic Gene Clusters (BGCs) in response to nutrient availability, oxidative stress, or quorum sensing signals. The Streptomyces genus, a prolific antibiotic producer, often employs Streptomyces Antibiotic Regulatory Proteins (SARPs), TetR-family repressors, and two-component regulatory systems to fine-tune the timing and level of antibiotic production [23]. These mechanisms are tightly linked to the organism’s metabolic state and ensure that the energy-intensive process of secondary metabolite synthesis occurs only under favorable conditions.

Beyond regulation, tailoring enzymes significantly expand the chemical diversity and potency of antibiotics through post-synthetic modifications. These include hydroxylation, methylation, glycosylation, acylation, halogenation, and cross-linking reactions. For example, glycopeptide antibiotics such as vancomycin and teicoplanin undergo elaborate oxidative crosslinking catalyzed by cytochrome P450 monooxygenases, as well as chlorination by flavin- dependent halogenases. These transformations are critical for the correct three-dimensional structure and antimicrobial function of the molecule [13]. Methyltransferases, acting on specific hydroxyl or amino groups, influence both solubility and binding affinity to bacterial targets. In erythromycin biosynthesis, the methylation of desosamine sugar moieties by DesVIII family methyltransferases enhances ribosomal binding and bioactivity [14].

Many of these tailoring enzymes act after the core scaffold has been assembled by NRPS or PKS enzymes, and are often encoded within the same biosynthetic gene cluster. Their sequential activity is sometimes rate-limiting, making them prime targets for metabolic engineering aimed at improving production yields. Genetic manipulation of these enzymes-such as overexpression, replacement, or deletion-has been used to create novel antibiotic analogs with altered properties or to increase fermentation efficiency in industrial strains [3].

Additionally, antibiotic-producing organisms encode self-resistance genes within their BGCs to avoid autotoxicity. These may include target-modifying enzymes, antibiotic-inactivating proteins, or efflux pumps. For example, the vanHAX gene cluster in Streptomyces species confers resistance to vancomycin by modifying the peptidoglycan precursor from D-Ala-D-Ala to D-Ala-D-Lac, thereby reducing drug binding affinity [24]. Similarly, chloramphenicol- producing bacteria harbor acetyltransferases that inactivate the compound by acetylation, and these resistance genes are tightly co-regulated with biosynthetic genes to prevent premature host damage [25].

Overall, the presence and coordinated activity of regulatory and tailoring enzymes are indispensable for successful antibiotic biosynthesis. They enable the generation of chemically diverse and bioactive molecules, while also ensuring that the producing organism is protected from the toxic effects of its own metabolites. Unraveling the complexity of these accessory enzymes not only provides insights into microbial evolution but also offers powerful tools for synthetic biology and industrial biotechnology.

Advancements in biotechnology have revolutionized the study and exploitation of antibiotic biosynthesis, particularly through modern techniques such as genome mining, CRISPR-Cas9 mediated gene editing, and heterologous expression systems. Genome mining allows researchers to systematically analyze vast datasets of microbial genomes and metagenomes to identify Biosynthetic Gene Clusters (BGCs) encoding Non-Ribosomal Peptide Synthetases (NRPS), Polyketide Synthases (PKS), or hybrid pathways that may produce novel bioactive compounds. This approach has greatly expanded the repertoire of potential antibiotic candidates by uncovering “cryptic” or silent gene clusters that are not expressed under standard laboratory conditions [26].

The advent of CRISPR-Cas9 technology has provided a powerful tool for precise manipulation of biosynthetic genes within native or heterologous hosts. By enabling targeted deletions, insertions, or modifications in NRPS and PKS gene clusters, CRISPR-based approaches facilitate functional characterization of enzymatic domains and regulatory elements, as well as pathway refactoring to enhance production yields. For example, targeted editing of promoter regions or transcriptional regulators can activate silent clusters, while domain replacement can be used to alter substrate specificity and generate novel chemical scaffolds [27].

Heterologous expression platforms, such as Streptomyces coelicolor or Escherichia coli, are widely employed to express BGCs derived from uncultivable or slow-growing microorganisms. These model organisms are genetically tractable and can be engineered to supply necessary precursors, cofactors, and regulatory proteins to support efficient antibiotic biosynthesis. Successful heterologous production of complex NRPS and PKS-derived compounds has enabled detailed biochemical studies and scalable production of rare or new antibiotics [28].

Synthetic biology approaches have further expanded the capacity to engineer antibiotic biosynthesis through rational design strategies. Given the modular architecture of NRPS and PKS enzymes, domain swapping and module recombination techniques allow researchers to reprogram assembly lines to incorporate alternative substrates or generate entirely novel molecules. This modularity provides a versatile framework for combinatorial biosynthesis, where modules from different sources are combined to yield “unnatural” natural products with improved pharmacological profiles, including enhanced potency, reduced toxicity, or broader antimicrobial spectra [4]. For instance, chimeric NRPS-PKS systems have been constructed to produce novel macrolide or lipopeptide antibiotics with tailored functionalities.

Despite these promising developments, challenges remain in optimizing inter-domain communication, maintaining enzyme stability, and achieving high yields of engineered products. However, ongoing advances in computational modeling, high-throughput screening, and metabolomics are expected to overcome these obstacles, accelerating the translation of engineered antibiotic biosynthetic pathways into clinically relevant therapies. Thus, the integration of genome mining, precise genetic editing, heterologous expression, and synthetic biology holds immense potential for addressing the global threat of antibiotic resistance by facilitating the discovery and production of new antimicrobial agents.

Conclusion

Enzyme systems such as NRPSs, PKSs, and their hybrids are central to antibiotic biosynthesis. Their modular and programmable nature makes them attractive targets for engineering novel antibiotics to combat antimicrobial resistance. A deeper understanding of their structure and mechanism continues to transform the field of natural product chemistry and pharmaceutical biotechnology

Acknowledgement

None.

Conflict of Interest

None.

References

1. Hutchings MI, Truman AW, Wilkinson B (2019) Antibiotics: past, present and future. Current Opinion in Microbiology 51: 72-80.
2. Barka EA, Vatsa P, Sanche, L, Nathalie Gaveau Vaillant, Cedric Jacquard, et al. (2016) Taxonomy, physiology, and natural products of Actinobacteria. Microbiology and Molecular Biology Reviews 80(1): 1-43.
3. Medema MH, Fischbach MA (2015) Computational approaches to natural product discovery. Nature Chemical Biology 11: 639-648.
4. Staunton J, Weissman KJ (2001) Polyketide biosynthesis: a millennium review. Natural Product Reports 18(4): 380-416.
5. Süssmuth RD, Mainz A (2017) Nonribosomal peptide synthesis-principles and prospects. Angewandte Chemie International Edition 56(14): 3770-3821.
6. Stephanie Galanie, David Entwistle, James Lalonde (2020) Engineering biosynthetic enzymes for industrial natural product synthesis. Nat Prod Rep 37(8): 1122-1143.
7. Brakhage AA (2013) Regulation of fungal secondary metabolism. Nature Reviews Microbiology 11: 21-32.
8. Yim G, Thaker MN, Koteva K, Wright GD (2014) Glycopeptide antibiotic biosynthesis. Journal of Antibiotics 67(1): 31-41.
9. Finking R, Marahiel MA (2004) Biosynthesis of nonribosomal peptides. Annual Review of Microbiology 58: 453-488.
10. Hur GH, Vickery CR, Burkart MD (2012) Explorations of catalytic domains in non-ribosomal peptide synthetase enzymology. Natural Product Reports 29(10): 1074-1098.
11. Strieker M, Tanović A, Marahiel MA (2010) Nonribosomal peptide synthetases: structures and dynamics. Current Opinion in Structural Biology 20(2): 234-240.
12. Sieber SA, Marahiel MA (2005) Molecular mechanisms underlying nonribosomal peptide synthesis: approaches to new antibiotics. Chemical Reviews 105(2): 715-738.
13. Walsh CT, Fischbach MA (2010) Natural products version 2.0: connecting genes to molecules. Journal of the American Chemical Society 132(8): 2469-2493.
14. Weissman KJ (2016) Genetic engineering of modular PKSs: from combinatorial biosynthesis to synthetic biology. Natural Product Reports 33(2): 203-230.
15. Hertweck C (2009) The biosynthetic logic of polyketide diversity. Angewandte Chemie International Edition 48(26): 4688-4716.
16. Cortés J, SF Haydock, GA Roberts, DJ Bevitt, PF Leadlay, et al. (1990). An unusually large multifunctional polypeptide in the erythromycin-producing polyketide synthase of Saccharopolyspora erythraea. Nature 348(6297): 176-178.
17. Gavin J Williams (2013) Engineering polyketide synthases and nonribosomal peptide synthetases. Curr Opin Struct Biol 23(4): 603-612.
18. Austin MB, Noel JP (2003) The chalcone synthase superfamily of type III polyketide synthases. Natural Product Reports 20(1): 79–110.
19. Weissman KJ, Leadlay PF (2005) Combinatorial biosynthesis of reduced polyketides. Nature Reviews Microbiology 3(12): 925-936.
20. Fischbach MA, Walsh CT (2006) Assembly-line enzymology for polyketide and nonribosomal peptide antibiotics: logic, machinery, and mechanisms. Chemical Reviews 106(8): 3468-3496.
21. Ben Shen, Liangcheng Du, Cesar Sanchez, Daniel J Edwards, Mei Chen, et al. (2002) Cloning and characterization of the bleomycin biosynthetic gene cluster from Streptomyces verticillus ATCC15003. J Nat Prod 65(3): 422-31.
22. Ayuso-Sacido A, Genilloud O (2005) New PCR primers for the screening of NRPS and PKS-I systems in actinomycetes: detection and distribution of these biosynthetic gene sequences in major taxonomic groups. Microbial Ecology 49(1): 10-24.
23. Helga U van der Heul, Bohdan L Bilyk, Kenneth J McDowall, Ryan F Seipke, Gilles P van Wezel (2018) Regulation of antibiotic production in Actinobacteria: new perspectives from the post-genomic era. Nat Prod Rep 35(6): 575-604.
24. Arthur M, Courvalin P (1993) Genetics and mechanisms of glycopeptide resistance in enterococci. Antimicrobial Agents and Chemotherapy 37(8): 1563-1571.
25. Cundliffe E (1989) How antibiotic-producing organisms avoid suicide. Annual Review of Microbiology 43(1): 207-233.
26. CimermancicP, Marnix H Medema, Jan Claesen, Kenji Kurita, Laura C Wieland Brown, et al. (2014) Insights into secondary metabolism from a global analysis of prokaryotic biosynthetic gene clusters. Cell 158(2): 412-421.
27. Cobb RE, Wang Y, Zhao H (2015) High-efficiency multiplex genome editing of Streptomyces species using an engineered CRISPR/Cas system. ACS Synthetic Biology 4(6): 723-728.
28. Gomez-Escribano JP, Bibb MJ (2011) Engineering Streptomyces coelicolor for heterologous expression of secondary metabolite gene clusters. Microbial Biotechnology 4(2): L207-215.