The Streptomyces leeuwenhoekii genome: de novo sequencing and assembly in single contigs of the chromosome, circular plasmid pSLE1 and linear plasmid pSLE2

Antimicrobials: An update on new strategies to diversify treatment for bacterial infections

Ninety-five years after Fleming's discovery of penicillin, a bounty of antibiotic compounds have been discovered, modified, or synthesised. Diversification of target sites, improved stability and altered activity spectra have enabled continued antibiotic efficacy, but overwhelming reliance and misuse has fuelled the global spread of antimicrobial resistance (AMR). An estimated 1.27 million deaths were attributable to antibiotic resistant bacteria in 2019, representing a major threat to modern medicine. Although antibiotics remain at the heart of strategies for treatment and control of bacterial diseases, the threat of AMR has reached catastrophic proportions urgently calling for fresh innovation. The last decade has been peppered with ground-breaking developments in genome sequencing, high throughput screening technologies and machine learning. These advances have opened new doors for bioprospecting for novel antimicrobials. They have also enabled more thorough exploration of complex and polymicrobial infections and interactions with the healthy microbiome. Using models of infection that more closely resemble the infection state in vivo, we are now beginning to measure the impacts of antimicrobial therapy on host/microbiota/pathogen interactions. However new approaches are needed for developing and standardising appropriate methods to measure efficacy of novel antimicrobial combinations in these contexts. A battery of promising new antimicrobials is now in various stages of development including co-administered inhibitors, phages, nanoparticles, immunotherapy, anti-biofilm and anti-virulence agents. These novel therapeutics need multidisciplinary collaboration and new ways of thinking to bring them into large scale clinical use.

Draft Genome Sequence of the Marine-Derived, Anticancer Compound-Producing Bacterium Streptomyces sp. Strain GMY01

The marine Streptomyces sp. strain GMY01 was isolated from Indonesian marine sediment. Genome mining analysis revealed that GMY01 has 28 biosynthetic gene clusters, dominated by genes encoding nonribosomal peptide synthetase and polyketide synthase.

Next-Generation Sequencing Applications for the Study of Fungal Pathogens

Next-generation sequencing (NGS) has become a widely used technology in biological research. NGS applications for clinical pathogen detection have become vital technologies. It is increasingly common to perform fast, accurate, and specific detection of clinical specimens using NGS. Pathogenic fungi with high virulence and drug resistance cause life-threatening clinical infections. NGS has had a significant biotechnological impact on detecting bacteria and viruses but is not equally applicable to fungi. There is a particularly urgent clinical need to use NGS to help identify fungi causing infections and prevent negative impacts. This review summarizes current research on NGS applications for fungi and offers a visual method of fungal detection. With the development of NGS and solutions for overcoming sequencing limitations, we suggest clinicians test specimens as soon as possible when encountering infections of unknown cause, suspected infections in vital organs, or rapidly progressive disease.

Revealing Genome-Based Biosynthetic Potential of Streptomyces sp. BR123 Isolated from Sunflower Rhizosphere with Broad Spectrum Antimicrobial Activity

Actinomycetes, most notably the genus Streptomyces, have great importance due to their role in the discovery of new natural products, especially for finding antimicrobial secondary metabolites that are useful in the medicinal science and biotechnology industries. In the current study, a genome-based evaluation of Streptomyces sp. isolate BR123 was analyzed to determine its biosynthetic potential, based on its in vitro antimicrobial activity against a broad range of microbial pathogens, including gram-positive and gram-negative bacteria and fungi. A draft genome sequence of 8.15 Mb of Streptomyces sp. isolate BR123 was attained, containing a GC content of 72.63% and 8103 protein coding genes. Many antimicrobial, antiparasitic, and anticancerous compounds were detected by the presence of multiple biosynthetic gene clusters, which was predicted by in silico analysis. A novel metabolite with a molecular mass of 1271.7773 in positive ion mode was detected through a high-performance liquid chromatography linked with mass spectrometry (HPLC-MS) analysis. In addition, another compound, meridamycin, was also identified through a HPLC-MS analysis. The current study reveals the biosynthetic potential of Streptomyces sp. isolate BR123, with respect to the synthesis of bioactive secondary metabolites through genomic and spectrometric analysis. Moreover, the comparative genome study compared the isolate BR123 with other Streptomyces strains, which may expand the knowledge concerning the mechanism involved in novel antimicrobial metabolite synthesis.

Genome editing reveals that pSCL4 is required for chromosome linearity in Streptomyces clavuligerus

Streptomyces clavuligerus is an industrially important actinomycete whose genetic manipulation is limited by low transformation and conjugation efficiencies, low levels of recombination of introduced DNA, and difficulty in obtaining consistent sporulation. We describe the construction and application of versatile vectors for Cas9-mediated genome editing of this strain. To design spacer sequences with confidence, we derived a highly accurate genome assembly for an isolate of the type strain (ATCC 27064). This yielded a chromosome assembly (6.75 Mb) plus assemblies for pSCL4 (1795 kb) and pSCL2 (149 kb). The strain also carries pSCL1 (12 kb), but its small size resulted in only partial sequence coverage. The previously described pSCL3 (444 kb) is not present in this isolate. Using our Cas9 vectors, we cured pSCL4 with high efficiency by targeting the plasmid's parB gene. Five of the resulting pSCL4-cured isolates were characterized and all showed impaired sporulation. Shotgun genome sequencing of each of these derivatives revealed large deletions at the ends of the chromosomes in all of them, and for two clones sufficient sequence data was obtained to show that the chromosome had circularized. Taken together, these data indicate that pSCL4 is essential for the structural stability of the linear chromosome.

Streptomyces venezuelae NRRL B-65442: genome sequence of a model strain used to study morphological differentiation in filamentous actinobacteria

For over a decade, Streptomyces venezuelae has been used to study the molecular mechanisms that control morphological development in streptomycetes and it is now a well-established model strain. Its rapid growth and ability to sporulate in a near-synchronised manner in liquid culture, unusual among streptomycetes, greatly facilitates the application of modern molecular techniques such as ChIP-seq and RNA-seq, as well as fluorescence time-lapse imaging of the complete Streptomyces life cycle. Here we describe a high-quality genome sequence of our isolate of the strain (NRRL B-65442) consisting of an 8.2 Mb chromosome and a 158 kb plasmid, pSVJI1, which had not been reported previously. Surprisingly, while NRRL B-65442 yields green spores on MYM agar, the ATCC type strain 10712 (from which NRRL B-65442 was derived) produces grey spores. While comparison of the genome sequences of the two isolates revealed almost total identity, it did reveal a single nucleotide substitution in a gene, vnz_33525, likely to be involved in spore pigment biosynthesis. Replacement of the vnz_33525 allele of ATCC 10712 with that of NRRL B-65442 resulted in green spores, explaining the discrepancy in spore pigmentation. We also applied CRISPR-Cas9 to delete the essential parB of pSVJI1 to cure the plasmid from the strain without obvious phenotypic consequences.

Antibacterial Performance of a Streptomyces spectabilis Strain Producing Metacycloprodigiosin

After separation of bacterial colonies on solid plates, purification, and screening through the agar cup-plate method, an antibiotic-resistant bacterial isolate was obtained, and named strain L20190601, the 16S rRNA gene sequence data of strain L20190601 to GenBank, NCBI have provided GenBank accession number MW931615. 16S rRNA gene sequencing revealed that this isolate was highly similar to a number of Streptomyces species. Among them, the homology with S. spectabilis was the highest, reaching 99.9, together with curved hyphal morphology and biochemical tests, allowed us to identify strain L20190601 as S. spectabilis. The red pigment produced by S. spectabilis strain L20190601 was structurally identified. An acid-base color reaction assay showed that when this pigment was dissolved in a solution at pH 3.0 and 9.0, the color of the solution was red and yellow, respectively. In addition, the analysis of absorption spectra revealed that at pH 8.0 and 3.0, the maximum absorption peaks were at 466 and 531 nm, respectively. These results are consistent with the spectral absorption characteristics of metacycloprodigiosin reported in the literature. Moreover, the retention time of purified pigments was identical to those of standard metacycloprodigiosin solutions. Mass spectrometry analysis revealed that the molecular weight of the red compound was 392.2 [M + H]⁺. Finally, metacycloprodigiosin was found to be effective against eight clinically common pathogens: Staphylococcus aureus, Bacillus subtilis, Escherichia coli, Streptococcus pyogenes, Pseudomonas aeruginosa, Bacillus typhi, Candida albicans, and Trichophyton rubrum. In summary, metacycloprodigiosin exhibited strong antibacterial activity and a broad antibacterial spectrum, and thus is a promising compound for the development of a new type of antibacterial drug.

Characterization of a Deep Sea Bacillus toyonensis Isolate: Genomic and Pathogenic Features

Bacillus toyonensis is a group of Gram-positive bacteria belonging to the Bacillus cereus group and used in some cases as probiotics or biocontrol agents. To our knowledge, B. toyonensis from the deep sea (depth >1,000 m) has not been documented. Here, we report the isolation and characterization of a B. toyonensis strain, P18, from a deep sea hydrothermal field. P18 is aerobic, motile, and able to grow at low temperatures (4°C) and high concentrations of NaCl (8%). P18 possesses a circular chromosome of 5,250,895 bp and a plasmid of 536,892 bp, which encode 5,380 and 523 genes, respectively. Of these genes, 2,229 encode hypothetical proteins that could not be annotated based on the COG database. Comparative genomic analysis showed that P18 is most closely related to the type strain of B. toyonensis, BCT-7112^T. Compared to BCT-7112^T, P18 contains 1,401 unique genes, 441 of which were classified into 20 COG functional categories, and the remaining 960 genes could not be annotated. A total of 319 putative virulence genes were identified in P18, including toxin-related genes, and 24 of these genes are absent in BCT-7112^T. P18 exerted strong cytopathic effects on fish and mammalian cells that led to rapid cell death. When inoculated via injection into fish and mice, P18 rapidly disseminated in host tissues and induced acute infection and mortality. Histopathology revealed varying degrees of tissue lesions in the infected animals. Furthermore, P18 could survive in fish and mouse sera and possessed hemolytic activity. Taken together, these results provide the first evidence that virulent B. toyonensis exists in deep sea environments.

Genome-guided investigation of secondary metabolites produced by a potential new strain Streptomyces BA2 isolated from an endemic plant rhizosphere in Turkey

Terrestrial actinomycetes are the important sources of secondary metabolites that serve as a major source of drugs. Recent advances in genome mining have revealed that Streptomyces genomes have a wide range of undiscovered secondary metabolite biosynthetic gene clusters. In the present study, genome mining was employed to discover biosynthetic potential of plant-associated strain Streptomyces BA2. Based on 16S rRNA gene sequencing, this strain was found to be closely related to Streptomyces durmitorensis, Streptomyces alboniger, and Streptomyces kanamyceticus with similarity of 99.71%, 99.64%, and 99.56%, respectively. The genome of BA2 contained 10.043.478 base pairs with G + C content of 69.92%. The annotation results revealed the presence of 9.056 protein coding genes, 88 tRNA and 18 rRNA genes. The dDDH and ANI values of genome sequences between strain BA2 and closely related type strains were considerably lower than the recommended threshold values. A total of 33 secondary metabolite biosynthetic gene clusters responsible for the biosynthesis of known and/or novel secondary metabolites, including non-ribosomal peptides, polyketides, terpenes, siderophores, bacteriocins, ectoines, and lassopeptides were identified. Metabolic profiling of Streptomyces sp. BA2 grown in three different culture media was determined by a non-targeted LC-MS/MS approach coupled with spectral networking. Significant bioactive natural products such as actinomycin D, desferrioxamine E, malyngamide K, and bouillonamide B were detected. Malyngamide K and bouillonamide B, known as marine cyanobacterial-derived compounds, were first reported from a Streptomyces strain in this study. Our study demonstrated the potentially novel strain Streptomyces sp. BA2 as a valuable source of new bioactive secondary metabolites.

Streptomyces harenosi sp. nov., a home for a gifted strain isolated from Indonesian sand dune soil

A polyphasic study was undertaken to establish the position of a Streptomyces strain, isolate PRKS01-65T, recovered from sand dune soil collected at Parangkusumo, Yogyakarta Province, Java, Indonesia. A combination of chemotaxonomic, cultural and morphological properties confirmed its position in the genus of Streptomyces. Comparative 16S rRNA gene sequence analyses showed that the isolate was most closely related to Streptomyces leeuwenhoekii C34T (99.9 % similarity) and loosely associated with the type strains of Streptomyces chiangmaiensis (98.7 % similarity) and Streptomyces glomeratus (98.9 % similarity). Multilocus sequence analyses based on five conserved housekeeping gene alleles confirmed the close relationship between the isolate and S. leeuwenhoekii C34T, although both strains belonged to a well-supported clade that encompassed the type strains of S. glomeratus, Streptomyces griseomycini, Streptomyces griseostramineus, Streptomyces labedae, Streptomyces lomondensis and Streptomyces spinoverrucosus. A comparison of the draft genome sequence generated for the isolate with corresponding whole genome sequences of its closest phylogenomic neighbours showed that it formed a well-separated lineage with S. leeuwenhoekii C34T. These strains can also be distinguished using a combination of phenotypic properties and by average nucleotide identity and digital DNA-DNA hybridization similarities of 94.3 and 56 %, values consistent with their classification in different species. Based on this wealth of data it is proposed that isolate PRKS01-65T (=NCIMB 15211T=CCMM B1302T=ICEBB-03T) be classified as Streptomyces harenosi sp. nov. The genome of the isolate contains several biosynthetic gene clusters with the potential to produce new natural products.

Dark, rare and inspirational microbial matter in the extremobiosphere: 16 000 m of bioprospecting campaigns

The rationale of our bioprospecting campaigns is that the extremobiosphere, particularly the deep sea and hyper-arid deserts, harbours undiscovered biodiversity that is likely to express novel chemistry and biocatalysts thereby providing opportunities for therapeutic drug and industrial process development. We have focused on actinobacteria because of their frequent role as keystone species in soil ecosystems and their unrivalled track record as a source of bioactive compounds. Population numbers and diversity of actinobacteria in the extremobiosphere are traditionally considered to be low, although they often comprise the dominant bacterial biota. Recent metagenomic evaluation of 'the uncultured microbial majority' has now revealed enormous taxonomic diversity among 'dark' and 'rare' actinobacteria in samples as diverse as sediments from the depths of the Mariana Trench and soils from the heights of the Central Andes. The application of innovative culture and screening options that emphasize rigorous dereplication at each stage of the analysis, and strain prioritization to identify 'gifted' organisms, have been deployed to detect and characterize bioactive hit compounds and sought-after catalysts from this hitherto untapped resource. The rewards include first-in-a-class chemical entities with novel modes of action, as well as a growing microbial seed bank that represents a potentially enormous source of biotechnological and therapeutic innovation.

Complete genome sequences of Streptomyces spp. isolated from disease-suppressive soils

Background

Bacteria within the genus Streptomyces remain a major source of new natural product discovery and as soil inoculants in agriculture where they promote plant growth and protect from disease. Recently, Streptomyces spp. have been implicated as important members of naturally disease-suppressive soils. To shine more light on the ecology and evolution of disease-suppressive microbial communities, we have sequenced the genome of three Streptomyces strains isolated from disease-suppressive soils and compared them to previously sequenced isolates. Strains selected for sequencing had previously showed strong phenotypes in competition or signaling assays.

Results

Here we present the de novo sequencing of three strains of the genus Streptomyces isolated from disease-suppressive soils to produce high-quality complete genomes. Streptomyces sp. GS93–23, Streptomyces sp. 3211–3, and Streptomyces sp. S3–4 were found to have linear chromosomes of 8.24 Mb, 8.23 Mb, and greater than 7.5 Mb, respectively. In addition, two of the strains were found to have large, linear plasmids. Each strain harbors between 26 and 38 natural product biosynthetic gene clusters, on par with previously sequenced Streptomyces spp. We compared these newly sequenced genomes with those of previously sequenced organisms. We see substantial natural product biosynthetic diversity between closely related strains, with the gain/loss of episomal DNA elements being a primary driver of genome evolution.

Conclusions

Long read sequencing data facilitates large contig assembly for high-GC Streptomyces genomes. While the sample number is too small for a definitive conclusion, we do not see evidence that disease suppressive soil isolates are particularly privileged in terms of numbers of biosynthetic gene clusters. The strong sequence similarity between GS93–23 and previously isolated Streptomyces lydicus suggests that species recruitment may contribute to the evolution of disease-suppressive microbial communities.

Heterologous Expression of a Cryptic Gene Cluster from Streptomyces leeuwenhoekii C34T Yields a Novel Lasso Peptide, Leepeptin

Recent developments in genome sequencing combined with bioinformatic analysis have revealed that actinomycetes contain a plethora of unexpected BGCs and thus have the potential to produce many more natural products than previously thought. This reflects the inability to detect the production of these compounds under laboratory conditions, perhaps through the use of inappropriate growth media or the absence of the environmental cues required to elicit expression of the corresponding BGCs. One approach to overcoming this problem is to circumvent the regulatory mechanisms that control expression of the BGC in its natural host by deploying heterologous expression. The generally compact nature of lasso peptide BGCs makes them particularly amenable to this approach, and, in the example given here, analysis revealed a new member of the lasso peptide family of RiPPs. This approach should be readily applicable to other cryptic lasso peptide gene clusters and would also facilitate the design and production of nonnatural variants by changing the sequence encoding the core peptide, as has been achieved with other classes of RiPPs.

Analysis of the genome sequence of Streptomyces leeuwenhoekii C34^T identified biosynthetic gene clusters (BGCs) for three different lasso peptides (Lp1, Lp2, and Lp3) which were not known to be made by the strain. Lasso peptides represent relatively new members of the RiPP (ribosomally synthesized and posttranslationally modified peptides) family of natural products and have not been extensively studied. Lp3, whose production could be detected in culture supernatants from S. leeuwenhoekii C34^T and after heterologous expression of its BGC in Streptomyces coelicolor, is identical to the previously characterized chaxapeptin. Lp1, whose production could not be detected or achieved heterologously, appears to be identical to a recently identified member of the citrulassin family of lasso peptides. Since production of Lp2 by S. leeuwenhoekii C34^T was not observed, its BGC was also expressed in S. coelicolor. The lasso peptide was isolated and its structure confirmed by mass spectrometry and nuclear magnetic resonance analyses, revealing a novel structure that appears to represent a new family of lasso peptides.

IMPORTANCE Recent developments in genome sequencing combined with bioinformatic analysis have revealed that actinomycetes contain a plethora of unexpected BGCs and thus have the potential to produce many more natural products than previously thought. This reflects the inability to detect the production of these compounds under laboratory conditions, perhaps through the use of inappropriate growth media or the absence of the environmental cues required to elicit expression of the corresponding BGCs. One approach to overcoming this problem is to circumvent the regulatory mechanisms that control expression of the BGC in its natural host by deploying heterologous expression. The generally compact nature of lasso peptide BGCs makes them particularly amenable to this approach, and, in the example given here, analysis revealed a new member of the lasso peptide family of RiPPs. This approach should be readily applicable to other cryptic lasso peptide gene clusters and would also facilitate the design and production of nonnatural variants by changing the sequence encoding the core peptide, as has been achieved with other classes of RiPPs.

Atacama Database: a platform of the microbiome of the Atacama Desert

The Atacama Desert is one of the oldest and driest places on Earth. In the last decade, microbial richness and diversity has been acknowledged as an important biological resource of this region. Owing to the value of the microbial diversity apparent in potential biotechnology applications and conservation purposes, it is necessary to catalogue these microbial communities to promote research activities and help to preserve the wide range of ecological niches of the Atacama region. A prototype Atacama Database has been designed and it provides a description of the rich microbial diversity of the Atacama Desert, and helps to visualise available literature resources. Data has been collected, curated, and organised into several categories to generate a single record for each organism in the database that covers classification, isolation metadata, morphology, physiology, genome and metabolism information. The current version of Atacama Database contains 2302 microorganisms and includes cultured and uncultured organisms retrieved from different environments within the desert between 1984 and 2016. These organisms are distributed in bacterial, archaeal or eukaryotic domains, along with those that are unclassified taxonomically. The initial prototype of the Atacama Database includes a basic search and taxonomic and advanced search tools to allow identification and comparison of microbial populations, and space distribution within this biome. A geolocation search was implemented to visualise the microbial diversity of the ecological niches defined by sectors and extract general information of the sampling sites. This effort will aid understanding of the microbial ecology of the desert, microbial population dynamics, seasonal behaviour, impact of climate change over time, and reveal further biotechnological applications of these microorganisms. The Atacama Database is freely available at: https://www.atacamadb.cl.

Comparative Genomics of Marine Sponge-Derived Streptomyces spp. Isolates SM17 and SM18 With Their Closest Terrestrial Relatives Provides Novel Insights Into Environmental Niche Adaptations and Secondary Metabolite Biosynthesis Potential

The emergence of antibiotic resistant microorganisms has led to an increased need for the discovery and development of novel antimicrobial compounds. Frequent rediscovery of the same natural products (NPs) continues to decrease the likelihood of the discovery of new compounds from soil bacteria. Thus, efforts have shifted toward investigating microorganisms and their secondary metabolite biosynthesis potential, from diverse niche environments, such as those isolated from marine sponges. Here we investigated at the genomic level two Streptomyces spp. strains, namely SM17 and SM18, isolated from the marine sponge Haliclona simulans, with previously reported antimicrobial activity against clinically relevant pathogens; using single molecule real-time (SMRT) sequencing. We performed a series of comparative genomic analyses on SM17 and SM18 with their closest terrestrial relatives, namely S. albus J1074 and S. pratensis ATCC 33331 respectively; in an effort to provide further insights into potential environmental niche adaptations (ENAs) of marine sponge-associated Streptomyces, and on how these adaptations might be linked to their secondary metabolite biosynthesis potential. Prediction of secondary metabolite biosynthetic gene clusters (smBGCs) indicated that, even though the marine isolates are closely related to their terrestrial counterparts at a genomic level; they potentially produce different compounds. SM17 and SM18 displayed a better ability to grow in high salinity medium when compared to their terrestrial counterparts, and further analysis of their genomes indicated that they possess a pool of 29 potential ENA genes that are absent in S. albus J1074 and S. pratensis ATCC 33331. This ENA gene pool included functional categories of genes that are likely to be related to niche adaptations and which could be grouped based on potential biological functions such as osmotic stress, defense; transcriptional regulation; symbiotic interactions; antimicrobial compound production and resistance; ABC transporters; together with horizontal gene transfer and defense-related features.

Extreme Environment Streptomyces: Potential Sources for New Antibacterial and Anticancer Drug Leads?

Antimicrobial resistance (AR) is recognized as one of the greatest threats to public health and in global concern. Consequently, the increased morbidity and mortality, which are associated with multidrug resistance bacteria, urgently require the discovery of novel and more efficient drugs. Conversely, cancer is a growing complex human disease that demands new drugs with no or fewer side effects. Most of the drugs currently used in the health care systems were of Streptomyces origin or their synthetic forms. Natural product researches from Streptomyces have been genuinely spectacular over the recent years from extreme environments. It is because of technical advances in isolation, fermentation, spectroscopy, and genomic studies which led to the efficient recovering of Streptomyces and their new chemical compounds with distinct activities. Expanding the use of the last line of antibiotics and demand for new drugs will continue to play an essential role for the potent Streptomyces from previously unexplored environmental sources. In this context, deep-sea, desert, cryo, and volcanic environments have proven to be a unique habitat of more extreme, and of their adaptation to extreme living, environments attribute to novel antibiotics. Extreme Streptomyces have been an excellent source of a new class of compounds which include alkaloids, angucycline, macrolide, and peptides. This review covers novel drug leads with antibacterial and cytotoxic activities isolated from deep-sea, desert, cryo, and volcanic environment Streptomyces from 2009 to 2019. The structure and chemical classes of the compounds, their relevant bioactivities, and the sources of organisms are presented.

The complete genomic sequence of Streptomyces spectabilis NRRL-2792 and identification of secondary metabolite biosynthetic gene clusters

This is the first report of a fully annotated genomic sequence of Streptomyces spectabilis NRRL-2792, isolated and identified by The Upjohn Company in 1961. The genome was assembled into a single scaffold for annotation and analysis. The chromosome is linear, 9.5 Mb in size which is one of the largest Streptomyces genomes yet described, has a G+C content of 72%, and encodes for approximately 7943 genes. Antibiotic Secondary Metabolite Analysis Shell (antiSMASH) and Basic Local Alignment Search Tool (BLAST) bioinformatics analyses identified six complete secondary metabolite biosynthetic gene clusters for ectoine, melanin, albaflavenone, spectinomycin, 2-methylisoborneol and coelichelin. Additionally, biosynthetic clusters were identified that shared ≥ 90% gene content with complestatin, hopene, neoaureothin, or undecylprodigiosin. Thirty-one other likely secondary metabolite gene clusters were identified by antiSMASH. BLAST identified two subsets of undecylprodigiosin biosynthetic genes at polar opposites of the chromosome; their duplication was subsequently confirmed by primer walking.

Natural product drug discovery in the genomic era: realities, conjectures, misconceptions, and opportunities

Natural product discovery from microorganisms provided important sources for antibiotics, anti-cancer agents, immune-modulators, anthelminthic agents, and insecticides during a span of 50 years starting in the 1940s, then became less productive because of rediscovery issues, low throughput, and lack of relevant new technologies to unveil less abundant or not easily detected drug-like natural products. In the early 2000s, it was observed from genome sequencing that Streptomyces species encode about ten times as many secondary metabolites as predicted from known secondary metabolomes. This gave rise to a new discovery approach—microbial genome mining. As the cost of genome sequencing dropped, the numbers of sequenced bacteria, fungi and archaea expanded dramatically, and bioinformatic methods were developed to rapidly scan whole genomes for the numbers, types, and novelty of secondary metabolite biosynthetic gene clusters. This methodology enabled the identification of microbial taxa gifted for the biosynthesis of drug-like secondary metabolites. As genome sequencing technology progressed, the realities relevant to drug discovery have emerged, the conjectures and misconceptions have been clarified, and opportunities to reinvigorate microbial drug discovery have crystallized. This perspective addresses these critical issues for drug discovery.

Impacts of horizontal gene transfer on the compact genome of the clavulanic acid-producing Streptomyces strain F613-1

Mobile genetic elements involved in mediating horizontal transfer events contribute to bacterial evolution, and bacterial genomic plasticity and instability result in variation in functional genetic information in Streptomyces secondary metabolism. In a previous study, we reported the complete genome sequence of the industrial Streptomyces strain F613-1, which produces high yields of clavulanic acid. In this study, we used comparative genomics and bioinformatics to investigate the unique genomic features of this strain. Taken together, comparative genomics were used to systematically investigate secondary metabolism capabilities and indicated that frequent exchange of genetic materials between Streptomyces replicons may shape the remarkable diversities in their secondary metabolite repertoires. Moreover, a 136.9-kb giant region of plasticity (RGP) was found in the F613-1 chromosome, and the chromosome and plasmid pSCL4 are densely packed with an exceptionally large variety of potential secondary metabolic gene clusters, involving several determinants putatively accounting for antibiotic production. In addition, the differences in the architecture and size of plasmid pSCL4 between F613-1 and ATCC 27064 suggest that the pSCL4 plasmid could evolve from pSCL4-like and pSCL2-like extrachromosomal replicons. Furthermore, the genomic analyses revealed that strain F613-1 has developed specific genomic architectures and genetic patterns that are well suited to meet the requirements of industrial innovation processes.

Mining the Genome of Streptomyces leeuwenhoekii: Two New Type I Baeyer-Villiger Monooxygenases From Atacama Desert

Actinobacteria are an important source of commercial (bio)compounds for the biotechnological and pharmaceutical industry. They have also been successfully exploited in the search of novel biocatalysts. We set out to explore a recently identified actinomycete, Streptomyces leeuwenhoekii C34, isolated from a hyper-arid region, the Atacama desert, for Baeyer–Villiger monooxygenases (BVMOs). Such oxidative enzymes are known for their broad applicability as biocatalysts by being able to perform various chemical reactions with high chemo-, regio-, and/or enantioselectivity. By choosing this specific Actinobacterium, which comes from an extreme environment, the respective enzymes are also expected to display attractive features by tolerating harsh conditions. In this work, we identified two genes in the genome of S. leeuwenhoekii (sle_13190 and sle_62070) that were predicted to encode for Type I BVMOs, the respective flavoproteins share 49% sequence identity. The two genes were cloned, overexpressed in E. coli with phosphite dehydrogenase (PTDH) as fusion partner and successfully purified. Both flavin-containing proteins showed NADPH-dependent Baeyer–Villiger oxidation activity for various ketones and sulfoxidation activity with some sulfides. Gratifyingly, both enzymes were found to be rather robust by displaying a relatively high apparent melting temperature (45°C) and tolerating water-miscible cosolvents. Specifically, Sle_62070 was found to be highly active with cyclic ketones and displayed a high regioselectivity by producing only one lactone from 2-phenylcyclohexanone, and high enantioselectivity by producing only normal (-)-1S,5R and abnormal (-)-1R,5S lactones (ee > 99%) from bicyclo[3.2.0]hept-2-en-6-one. These two newly discovered BVMOs add two new potent biocatalysts to the known collection of BVMOs.

Blastococcus atacamensis sp. nov., a novel strain adapted to life in the Yungay core region of the Atacama Desert

A polyphasic study was undertaken to establish the taxonomic status of a Blastococcus strain isolated from an extreme hyper-arid Atacama Desert soil. The isolate, strain P6^T, was found to have chemotaxonomic and morphological properties consistent with its classification in the genus Blastococcus. It was shown to form a well-supported branch in the Blastococcus 16S rRNA gene tree together with the type strains of Blastococcus capsensis and Blastococcus saxobsidens and was distinguished from the latter, its close phylogenetic neighbour, by a broad range of phenotypic properties. The draft genome sequence of isolate P6^T showed 84.6 % average nucleotide identity, 83.0 % average amino acid identity and a digital DNA-DNA hybridisation value of 27.8 % in comparison with the genome sequence of B. saxobsidens DSM 44509^T, values consistent with its assignment to a separate species. Based on these data it is proposed that isolate P6^T (NCIMB 15090^T=NRRL B-65468^T) be assigned to the genus Blastococcus as Blastococcus atacamensis sp. nov. Analysis of the whole genome sequence of B. atacamensis P6^T, with 3778 open reading frames and a genome size of 3.9 Mb showed the presence of genes and gene clusters that encode for properties that reflect its adaptation to the extreme environmental conditions that prevail in Atacama Desert soils.

Rare taxa and dark microbial matter: novel bioactive actinobacteria abound in Atacama Desert soils

An "in house" taxonomic approach to drug discovery led to the isolation of diverse actinobacteria from hyper-arid, extreme hyper-arid and very high altitude Atacama Desert soils. A high proportion of the isolates were assigned to novel taxa, with many showing activity in standard antimicrobial plug assays. The application of more advanced taxonomic and screening strategies showed that strains classified as novel species of Lentzea and Streptomyces synthesised new specialised metabolites thereby underpinning the premise that the extreme abiotic conditions in the Atacama Desert favour the development of a unique actinobacterial diversity which is the basis of novel chemistry. Complementary metagenomic analyses showed that the soils encompassed an astonishing degree of actinobacterial 'dark matter', while rank-abundance analyses showed them to be highly diverse habitats mainly composed of rare taxa that have not been recovered using culture-dependent methods. The implications of these pioneering studies on future bioprospecting campaigns are discussed.

Analysis of metabolic networks of Streptomyces leeuwenhoekii C34 by means of a genome scale model: Prediction of modifications that enhance the production of specialized metabolites

The first genome scale model (GSM) for Streptomyces leeuwenhoekii C34 was developed to study the biosynthesis pathways of specialized metabolites and to find metabolic engineering targets for enhancing their production. The model, iVR1007, consists of 1,722 reactions, 1,463 metabolites, and 1,007 genes, it includes the biosynthesis pathways of chaxamycins, chaxalactins, desferrioxamines, ectoine, and other specialized metabolites. iVR1007 was validated using experimental information of growth on 166 different sources of carbon, nitrogen and phosphorous, showing an 83.7% accuracy. The model was used to predict metabolic engineering targets for enhancing the biosynthesis of chaxamycins and chaxalactins. Gene knockouts, such as sle03600 (L-homoserine O-acetyltransferase), and sle39090 (trehalose-phosphate synthase), that enhance the production of the specialized metabolites by increasing the pool of precursors were identified. Using the algorithm of flux scanning based on enforced objective flux (FSEOF) implemented in python, 35 and 25 over-expression targets for increasing the production of chaxamycin A and chaxalactin A, respectively, that were not directly associated with their biosynthesis routes were identified. Nineteen over-expression targets that were common to the two specialized metabolites studied, like the over-expression of the acetyl carboxylase complex (sle47660 (accA) and any of the following genes: sle44630 (accA_1) or sle39830 (accA_2) or sle27560 (bccA) or sle59710) were identified. The predicted knockouts and over-expression targets will be used to perform metabolic engineering of S. leeuwenhoekii C34 and obtain overproducer strains.

The 'gifted' actinomycete Streptomyces leeuwenhoekii

Streptomyces leeuwenhoekii strains C34^T, C38, C58 and C79 were isolated from a soil sample collected from the Chaxa Lagoon, located in the Salar de Atacama in northern Chile. These streptomycetes produce a variety of new specialised metabolites with antibiotic, anti-cancer and anti-inflammatory activities. Moreover, genome mining performed on two of these strains has revealed the presence of biosynthetic gene clusters with the potential to produce new specialised metabolites. This review focusses on this new clade of Streptomyces strains, summarises the literature and presents new information on strain C34^T.

Complete genome sequence of Streptomyces formicae KY5, the formicamycin producer

Here we report the complete genome of the new species Streptomyces formicae KY5 isolated from Tetraponera fungus growing ants. S. formicae was sequenced using the PacBio and 454 platforms to generate a single linear chromosome with terminal inverted repeats. Illumina MiSeq sequencing was used to correct base changes resulting from the high error rate associated with PacBio. The genome is 9.6 Mbps, has a GC content of 71.38% and contains 8162 protein coding sequences. Predictive analysis shows this strain encodes at least 45 gene clusters for the biosynthesis of secondary metabolites, including a type 2 polyketide synthase encoding cluster for the antibacterial formicamycins. Streptomyces formicae KY5 is a new, taxonomically distinct Streptomyces species and this complete genome sequence provides an important marker in the genus of Streptomyces.

Synthetic biology, genome mining, and combinatorial biosynthesis of NRPS-derived antibiotics: a perspective

Combinatorial biosynthesis of novel secondary metabolites derived from nonribosomal peptide synthetases (NRPSs) has been in slow development for about a quarter of a century. Progress has been hampered by the complexity of the giant multimodular multienzymes. More recently, advances have been made on understanding the chemical and structural biology of these complex megaenzymes, and on learning the design rules for engineering functional hybrid enzymes. In this perspective, I address what has been learned about successful engineering of complex lipopeptides related to daptomycin, and discuss how synthetic biology and microbial genome mining can converge to broaden the scope and enhance the speed and robustness of combinatorial biosynthesis of NRPS-derived natural products for drug discovery.

Complete Genome Sequence of Streptomyces sp. TN58, a Producer of Acyl Alpha-l-Rhamnopyranosides

Streptomyces sp. TN58, isolated from a Tunisian soil sample, produces several natural products, including acyl alpha-l-rhamnopyranosides. It possesses a 7.6-Mb linear chromosome. This is, to our knowledge, the first genome sequence of a microorganism known to produce acyl alpha-l-rhamnopyranosides, and it will be helpful to study the biosynthesis of these specialized metabolites.

Actinobacterial Rare Biospheres and Dark Matter Revealed in Habitats of the Chilean Atacama Desert

The Atacama Desert is the most extreme non-polar biome on Earth, the core region of which is considered to represent the dry limit for life and to be an analogue for Martian soils. This study focused on actinobacteria because they are keystone species in terrestrial ecosystems and are acknowledged as an unrivalled source of bioactive compounds. Metagenomic analyses of hyper-arid and extreme hyper-arid soils in this desert revealed a remarkable degree of actinobacterial 'dark matter', evidenced by a detected increase of 34% in families against those that are validly published. Rank-abundance analyses indicated that these soils were high-diversity habitats and that the great majority of designated 'rare' genera (up to 60% of all phylotypes) were always rare. These studies have enabled a core actinobacterial microbiome common to both habitats to be defined. The great majority of detected taxa have not been recovered by culture dependent methods, neither, with very few exceptions, has their functional ecology been explored. A microbial seed bank of this magnitude has significance not just for Atacama soil ecosystem resilience but represents an enormous untapped resource for biotechnology discovery programmes in an era where resistance to existing antibiotics is rapidly becoming a major threat to global health.

Whole genome sequence of two Rathayibacter toxicus strains reveals a tunicamycin biosynthetic cluster similar to Streptomyces chartreusis

Rathayibacter toxicus is a forage grass associated Gram-positive bacterium of major concern to food safety and agriculture. This species is listed by USDA-APHIS as a plant pathogen select agent because it produces a tunicamycin-like toxin that is lethal to livestock and may be vectored by nematode species native to the U.S. The complete genomes of two strains of R. toxicus, including the type strain FH-79, were sequenced and analyzed in comparison with all available, complete R. toxicus genomes. Genome sizes ranged from 2,343,780 to 2,394,755 nucleotides, with 2079 to 2137 predicted open reading frames; all four strains showed remarkable synteny over nearly the entire genome, with only a small transposed region. A cluster of genes with similarity to the tunicamycin biosynthetic cluster from Streptomyces chartreusis was identified. The tunicamycin gene cluster (TGC) in R. toxicus contained 14 genes in two transcriptional units, with all of the functional elements for tunicamycin biosynthesis present. The TGC had a significantly lower GC content (52%) than the rest of the genome (61.5%), suggesting that the TGC may have originated from a horizontal transfer event. Further analysis indicated numerous remnants of other potential horizontal transfer events are present in the genome. In addition to the TGC, genes potentially associated with carotenoid and exopolysaccharide production, bacteriocins and secondary metabolites were identified. A CRISPR array is evident. There were relatively few plant-associated cell-wall hydrolyzing enzymes, but there were numerous secreted serine proteases that share sequence homology to the pathogenicity-associated protein Pat-1 of Clavibacter michiganensis. Overall, the genome provides clear insight into the possible mechanisms for toxin production in R. toxicus, providing a basis for future genetic approaches.

The Atacama Desert: Technical Resources and the Growing Importance of Novel Microbial Diversity

The Atacama Desert of northern Chile is the oldest and most arid nonpolar environment on Earth. It is a coastal desert covering approximately 180,000 km(2), and together with the greater Atacama region it comprises a dramatically wide range of ecological niches. Long known and exploited for its mineral resources, the Atacama Desert harbors a rich microbial diversity that has only recently been discovered; the great majority of it has not yet been recovered in culture or even taxonomically identified. This review traces the progress of microbiology research in the Atacama and dispels the popular view that this region is virtually devoid of life. We examine reasons for such research activity and demonstrate that microbial life is the latest recognized and least explored resource in this inspiring biome.

Dual Induction of New Microbial Secondary Metabolites by Fungal Bacterial Co-cultivation

The frequent re-isolation of known compounds is one of the major challenges in drug discovery. Many biosynthetic genes are not expressed under standard culture conditions, thus limiting the chemical diversity of microbial compounds that can be obtained through fermentation. On the other hand, the competition during co-cultivation of two or more different microorganisms in most cases leads to an enhanced production of constitutively present compounds or an accumulation of cryptic compounds that are not detected in axenic cultures of the producing strain under different fermentation conditions. Herein, we report the dual induction of newly detected bacterial and fungal metabolites by the co-cultivation of the marine-derived fungal isolate Aspergillus fumigatus MR2012 and two hyper-arid desert bacterial isolates Streptomyces leeuwenhoekii strain C34 and strain C58. Co-cultivation of the fungal isolate MR2012 with the bacterial strain C34 led to the production of luteoride D, a new luteoride derivative and pseurotin G, a new pseurotin derivative in addition to the production of terezine D and 11-O-methylpseurotin A which were not traced before from this fungal strain under different fermentation conditions. In addition to the previously detected metabolites in strain C34, the lasso peptide chaxapeptin was isolated under co-culture conditions. The gene cluster for the latter compound had been identified through genome scanning, but it had never been detected before in the axenic culture of strain C34. Furthermore, when the fungus MR2012 was co-cultivated with the bacterial strain C58, the main producer of chaxapeptin, the titre of this metabolite was doubled, while additionally the bacterial metabolite pentalenic acid was detected and isolated for the first time from this strain, whereas the major fungal metabolites that were produced under axenic culture were suppressed. Finally, fermentation of the MR2012 by itself led to the isolation of the new diketopiperazine metabolite named brevianamide X.

Streptomyces aridus sp. nov., isolated from a high altitude Atacama Desert soil and emended description of Streptomyces noboritoensis Isono et al. 1957

A polyphasic study was undertaken to determine the taxonomic status of a Streptomyces strain which had been isolated from a high altitude Atacama Desert soil and shown to have bioactive properties. The strain, isolate H9^T, was found to have chemotaxonomic, cultural and morphological properties that place it in the genus Streptomyces. 16S rRNA gene sequence analyses showed that the isolate forms a distinct branch at the periphery of a well-delineated subclade in the Streptomyces 16S rRNA gene tree together with the type strains of Streptomyces crystallinus, Streptomyces melanogenes and Streptomyces noboritoensis. Multi-locus sequence analysis (MLSA) based on five house-keeping gene alleles showed that isolate H9^T is closely related to the latter two type strains and to Streptomyces polyantibioticus NRRL B-24448^T. The isolate was distinguished readily from the type strains of S. melanogenes, S. noboritoensis and S. polyantibioticus using a combination of phenotypic properties. Consequently, the isolate is considered to represent a new species of Streptomyces for which the name Streptomyces aridus sp. nov. is proposed; the type strain is H9^T (=NCIMB 14965^T=NRRL B65268^T). In addition, the MLSA and phenotypic data show that the S. melanogenes and S. noboritoensis type strains belong to a single species, it is proposed that S. melanogenes be recognised as a heterotypic synonym of S. noboritoensis for which an emended description is given.

Understanding the Pathogenicity of Burkholderia contaminans, an Emerging Pathogen in Cystic Fibrosis

Several bacterial species from the Burkholderia cepacia complex (Bcc) are feared opportunistic pathogens that lead to debilitating lung infections with a high risk of developing fatal septicemia in cystic fibrosis (CF) patients. However, the pathogenic potential of other Bcc species is yet unknown. To elucidate clinical relevance of Burkholderia contaminans, a species frequently isolated from CF respiratory samples in Ibero-American countries, we aimed to identify its key virulence factors possibly linked with an unfavorable clinical outcome. We performed a genome-wide comparative analysis of two isolates of B. contaminans ST872 from sputum and blood culture of a female CF patient in Argentina. RNA-seq data showed significant changes in expression for quorum sensing-regulated virulence factors and motility and chemotaxis. Furthermore, we detected expression changes in a recently described low-oxygen-activated (lxa) locus which encodes stress-related proteins, and for two clusters responsible for the biosynthesis of antifungal and hemolytic compounds pyrrolnitrin and occidiofungin. Based on phenotypic assays that confirmed changes in motility and in proteolytic, hemolytic and antifungal activities, we were able to distinguish two phenotypes of B. contaminans that coexisted in the host and entered her bloodstream. Whole genome sequencing revealed that the sputum and bloodstream isolates (each representing a distinct phenotype) differed by over 1,400 mutations as a result of a mismatch repair-deficient hypermutable state of the sputum isolate. The inferred lack of purifying selection against nonsynonymous mutations and the high rate of pseudogenization in the derived isolate indicated limited evolutionary pressure during evolution in the nutrient-rich, stable CF sputum environment. The present study is the first to examine the genomic and transcriptomic differences between longitudinal isolates of B. contaminans. Detected activity of a number of putative virulence factors implies a genuine pathogenic nature of this novel Bcc species.

Isolation and anti-HIV-1 integrase activity of lentzeosides A-F from extremotolerant lentzea sp. H45, a strain isolated from a high-altitude Atacama Desert soil

The extremotolerant isolate H45 was one of several actinomycetes isolated from a high-altitude Atacama Desert soil collected in northwest Chile. The isolate was identified as a new Lentzea sp. using a combination of chemotaxonomic, morphological and phylogenetic properties. Large scale fermentation of the strain in two different media followed by chromatographic purification led to the isolation of six new diene and monoene glycosides named lentzeosides A-F, together with the known compound (Z)-3-hexenyl glucoside. The structures of the new compounds were confirmed by HRESIMS and NMR analyses. Compounds 1-6 displayed moderate inhibitory activity against HIV integrase.

Function, expression, specificity, diversity and incompatibility of actinobacteriophage parABS systems

More than 180 individual phages infecting hosts in the phylum Actinobacteria have been sequenced and grouped into Cluster A because of their similar overall nucleotide sequences and genome architectures. These Cluster A phages are either temperate or derivatives of temperate parents, and most have an integration cassette near the centre of the genome containing an integrase gene and attP. However, about 20% of the phages lack an integration cassette, which is replaced by a 1.4 kbp segment with predicted partitioning functions, including plasmid-like parA and parB genes. Phage RedRock forms stable lysogens in Mycobacterium smegmatis in which the prophage replicates at 2.4 copies/chromosome and the partitioning system confers prophage maintenance. The parAB genes are expressed upon RedRock infection of M. smegmatis, but are downregulated once lysogeny is established by binding of RedRock ParB to parS-L, one of two centromere-like sites flanking the parAB genes. The RedRock parS-L and parS-R sites are composed of eight directly repeated copies of an 8 bp motif that is recognized by ParB. The actinobacteriophage parABS cassettes span considerable sequence diversity and specificity, providing a suite of tools for use in mycobacterial genetics.

Next Generation Sequencing of Actinobacteria for the Discovery of Novel Natural Products

Like many fields of the biosciences, actinomycete natural products research has been revolutionised by next-generation DNA sequencing (NGS). Hundreds of new genome sequences from actinobacteria are made public every year, many of them as a result of projects aimed at identifying new natural products and their biosynthetic pathways through genome mining. Advances in these technologies in the last five years have meant not only a reduction in the cost of whole genome sequencing, but also a substantial increase in the quality of the data, having moved from obtaining a draft genome sequence comprised of several hundred short contigs, sometimes of doubtful reliability, to the possibility of obtaining an almost complete and accurate chromosome sequence in a single contig, allowing a detailed study of gene clusters and the design of strategies for refactoring and full gene cluster synthesis. The impact that these technologies are having in the discovery and study of natural products from actinobacteria, including those from the marine environment, is only starting to be realised. In this review we provide a historical perspective of the field, analyse the strengths and limitations of the most relevant technologies, and share the insights acquired during our genome mining projects.

Deciphering the streamlined genome of Streptomyces xiamenensis 318 as the producer of the anti-fibrotic drug candidate xiamenmycin

Streptomyces xiamenensis 318, a moderate halophile isolated from a mangrove sediment, produces the anti-fibrotic compound xiamenmycin. The whole genome sequence of strain 318 was obtained through long-read single-molecule real-time (SMRT) sequencing, high-throughput Illumina HiSeq and 454 pyrosequencing technologies. The assembled genome comprises a linear chromosome as a single contig of 5,961,401-bp, which is considerably smaller than other reported complete genomes of the genus Streptomyces. Based on the antiSMASH pipeline, a total of 21 gene clusters were predicted to be involved in secondary metabolism. The gene cluster responsible for the biosynthesis of xiamenmycin resides in a strain-specific 61,387-bp genomic island belonging to the left-arm region. A core metabolic network consisting of 104 reactions that supports xiamenmycin biosynthesis was constructed to illustrate the necessary precursors derived from the central metabolic pathway. In accordance with the finding of a putative ikarugamycin gene cluster in the genome, the targeted chemical profiling of polycyclic tetramate macrolactams (PTMs) resulted in the identification of ikarugamycin. A successful genome mining for bioactive molecules with different skeletons suggests that the naturally minimized genome of S. xiamenensis 318 could be used as a blueprint for constructing a chassis cell with versatile biosynthetic capabilities for the production of secondary metabolites.

Biosynthesis of the Novel Macrolide Antibiotic Anthracimycin

We report the identification of the biosynthetic gene cluster for the unusual antibiotic anthracimycin (atc) from the marine derived producer strain Streptomyces sp. T676 isolated off St. John's Island, Singapore. The 53 253 bps atc locus includes a trans-acyltransferase (trans-AT) polyketide synthase (PKS), and heterologous expression in Streptomyces coelicolor resulted in anthracimycin production. Analysis of the atc cluster revealed that anthracimycin is likely generated by four PKS gene products AtcC-AtcF without involvement of post-PKS tailoring enzymes, and a biosynthetic pathway is proposed. The availability of the atc cluster provides a basis for investigating the biosynthesis of anthracimycin and its subsequent bioengineering to provide novel analogues with improved pharmacological properties.

Identification and Heterologous Expression of the Chaxamycin Biosynthesis Gene Cluster from Streptomyces leeuwenhoekii

Streptomyces leeuwenhoekii, isolated from the hyperarid Atacama Desert, produces the new ansamycin-like compounds chaxamycins A to D, which possess potent antibacterial activity and moderate antiproliferative activity. We report the development of genetic tools to manipulate S. leeuwenhoekii and the identification and partial characterization of the 80.2-kb chaxamycin biosynthesis gene cluster, which was achieved by both mutational analysis in the natural producer and heterologous expression in Streptomyces coelicolor A3(2) strain M1152. Restoration of chaxamycin production in a nonproducing ΔcxmK mutant (cxmK encodes 3-amino-5-hydroxybenzoic acid [AHBA] synthase) was achieved by supplementing the growth medium with AHBA, suggesting that mutasynthesis may be a viable approach for the generation of novel chaxamycin derivatives.