Structure elucidation of the syringafactin lipopeptides provides insight in the evolution of nonribosomal peptide synthetases

A chemical radar allows bacteria to detect and kill predators

Amoebal predation exerts a strong evolutionary selection pressure on bacteria, thus driving the development of effective predator-defense strategies. However, little is known about the molecular interplay between bacteria and predators, particularly how bacteria can sense and kill their microbial predators. We show how the ubiquitous bacterium Pseudomonas syringae detects and kills the social amoeba Polysphondylium pallidum. Combining comparative genomics, molecular biology, and chemical analyses, we identified a chemical radar system. The system relies on P. syringae secreting the lipopeptide syringafactin, which is deacylated by the amoeba. The resulting peptides are sensed via the bacterial sensor protein chemical radar regulator (CraR) that activates genes for converting the predator-derived signal into the amoebicide pyrofactin. This system is widespread in P. syringae and enables bacteria to infect A. thaliana in the presence of amoebae. Our study advances the understanding of microbial sensing and opens new avenues for the discovery of natural products.

Pangenome Analysis of the Plant Pathogen Pseudomonas syringae Reveals Unique Natural Products for Niche Adaptation

Pseudomonas syringae is a soil-dwelling bacterium that exhibits remarkable niche adaptability, and it is known for its devastating impact as a plant pathogen. This bacterium has an outstanding capability to produce a wide array of biologically active natural products. P. syringae coexists with amoebal predators and fungal strains, which drives the production of secondary metabolites for predator evasion in addition to niche adaptation. In this study, we conducted a broad pangenomic analysis of 18 taxonomically distinct P. syringae strains, leading to the identification of 231 biosynthetic gene clusters (BGCs). Among these, nonribosomal peptide synthetases (NRPSs) were particularly abundant, indicating their potential significance within this ecological context. We discovered and elucidated the structures of two novel classes of bioactive compounds, the syrilipamides and chlorosecimides. Furthermore, a bioinformatic analysis enabled the identification of an undescribed halogenase, SecA, essential for the chlorination of secimide A. We observed that syrilipamides and secimides and in particular mixtures thereof, exhibit amoebicidal activities. Additionally, secimides showed selective antifungal activity. These findings provide valuable insights into the ecological roles of P. syringae natural products and highlight their potential for biotechnological and therapeutic applications.

Total substitution and partial modification of the set of non-ribosomal peptide synthetases clusters lead to pyoverdine diversity in the Pseudomonas fluorescens complex

Pyoverdines are high affinity siderophores produced by most Pseudomonas with a wide role in microbial interspecies interactions. They are primarily composed of a conserved chromophore moiety, an acyl side chain and a peptide backbone which may be highly variable among strains. Upon ferric iron sequestration, pyoverdines are internalized through specialized receptors. The peptide precursor of pyoverdine, termed ferribactin, is synthesized by a set of non-ribosomal peptide synthetase (NRPS) enzymes and further modified by tailoring enzymes. While PvdL, the NRPS responsible for the synthesis of the peptide moiety that derives into the chromophore is conserved, the NRPSs for the peptide backbone are different across fluorescent Pseudomonas. Although the variation of pyoverdine is a widely recognized characteristic within the genus, the evolutionary events associated with the diversity and distribution of this trait remain mostly unknown. This study analyzed the NRPSs clusters for the biosynthesis of the peptide backbone of ferribactin in the genomes of a representative subset of strains of the Pseudomonas fluorescens complex. Bioinformatic analysis of the specificity of adenylation domains of the NRPSs allowed the prediction of 30 different pyoverdine variants. Phylogenetic reconstruction and mapping of the NRPS clusters pinpointed two different general levels of modifications. In the first level, a complete replacement of the set of NRPRs by horizontal transfer occurs. In the second level, the original set of NRPSs is modified through different mechanisms, including partial substitution of the NRPS genes by horizontal transfer, adenylation domain specificity change or NRPS accessory domain gain/loss.

Evolution-inspired engineering of nonribosomal peptide synthetases

Many clinically used drugs are derived from or inspired by bacterial natural products that often are produced through nonribosomal peptide synthetases (NRPSs), megasynthetases that activate and join individual amino acids in an assembly line fashion. In this work, we describe a detailed phylogenetic analysis of several bacterial NRPSs that led to the identification of yet undescribed recombination sites within the thiolation (T) domain that can be used for NRPS engineering. We then developed an evolution-inspired "eXchange Unit between T domains" (XUT) approach, which allows the assembly of NRPS fragments over a broad range of GC contents, protein similarities, and extender unit specificities, as demonstrated for the specific production of a proteasome inhibitor designed and assembled from five different NRPS fragments.

Stereomeric Lipopeptides from a Single Non-Ribosomal Peptide Synthetase as an Additional Source of Structural and Functional Diversification in Pseudomonas Lipopeptide Biosynthesis

In Pseudomonas lipopeptides, the D-configuration of amino acids is generated by dedicated, dual-function epimerization/condensation (E/C) domains. The increasing attention to stereochemistry in lipopeptide structure elucidation efforts has revealed multiple examples where epimerization does not occur, even though an E/C-type domain is present. While the origin of the idle epimerization in those E/C-domains remains elusive, epimerization activity has so far shown a binary profile: it is either 'on' (active) or 'off' (inactive). Here, we report the unprecedented observation of an E/C-domain that acts 'on and off', giving rise to the production of two diastereoisomeric lipopeptides by a single non-ribosomal peptide synthetase system. Using dereplication based on solid-phase peptide synthesis and NMR fingerprinting, we first show that the two cyclic lipopeptides produced by Pseudomonas entomophila COR5 correspond to entolysin A and B originally described for P. entomophila L48. Next, we prove that both are diastereoisomeric homologues differing only in the configuration of a single amino acid. This configurational variability is maintained in multiple Pseudomonas strains and typically occurs in a 3:2 ratio. Bioinformatic analysis reveals a possible correlation with the composition of the flanking sequence of the N-terminal secondary histidine motif characteristic for dual-function E/C-type domains. In permeabilization assays, using propidium iodide entolysin B has a higher antifungal activity compared to entolysin A against Botrytis cinerea and Pyricularia oryzae spores. The fact that configurational homologues are produced by the same NRPS system in a Pseudomonas strain adds a new level of structural and functional diversification to those already known from substrate flexibility during the recruitment of the amino acids and fatty acids and underscores the importance of complete stereochemical elucidation of non-ribosomal lipopeptide structures.

Biomimetic engineering of nonribosomal peptide synthesis

Nonribosomal peptides (NRPs) have gained attention due to their diverse biological activities and potential applications in medicine and agriculture. The natural diversity of NRPs is a result of evolutionary processes that have occurred over millions of years. Recent studies have shed light on the mechanisms by which nonribosomal peptide synthetases (NRPSs) evolve, including gene duplication, recombination, and horizontal transfer. Mimicking natural evolution could be a useful strategy for engineering NRPSs to produce novel compounds with desired properties. Furthermore, the emergence of antibiotic-resistant bacteria has highlighted the urgent need for new drugs, and NRPs represent a promising avenue for drug discovery. This review discusses the engineering potential of NRPSs in light of their evolutionary history.

Discovery of Cyclic Lipopeptides Ralstopeptins A and B from Ralstonia solanacearum Species Complex and Analysis of Biosynthetic Gene Evolution

Ralstonia solanacearum species complex (RSSC) strains are plant pathogens that produce lipopeptides (ralstonins and ralstoamides) by the polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) enzyme hybrid. Recently, ralstonins were found to be key molecules in the parasitism of RSSC to other hosts, Aspergillus and Fusarium fungi. The PKS-NRPS genes of RSSC strains in the GenBank database suggest the production of additional lipopeptides, although it has not been confirmed to date. Here, we report the genome-driven and mass-spectrometry-guided discovery, isolation, and structural elucidation of ralstopeptins A and B from strain MAFF 211519. Ralstopeptins were found to be cyclic lipopeptides with two amino acid residues less than ralstonins. The partial deletion of the gene encoding PKS-NRPS obliterated the production of ralstopeptins in MAFF 211519. Bioinformatic analyses suggested possible evolutionary events of the biosynthetic genes of RSSC lipopeptides, where intragenomic recombination may have occurred within the PKS-NRPS genes, reducing the gene size. The chlamydospore-inducing activities of ralstopeptins A and B, ralstonins A and B, and ralstoamide A in the fungus Fusarium oxysporum indicated a structural preference for ralstonins. Altogether, we propose a model for the evolutionary processes that contribute to the chemical diversity of RSSC lipopeptides and its relation to the endoparasitism of RSSC in fungi.

Charting the Lipopeptidome of Nonpathogenic Pseudomonas

A major source of pseudomonad-specialized metabolites is the nonribosomal peptide synthetases (NRPSs) assembling siderophores and lipopeptides. Cyclic lipopeptides (CLPs) of the Mycin and Peptin families are frequently associated with, but not restricted to, phytopathogenic species. We conducted an in silico analysis of the NRPSs encoded by lipopeptide biosynthetic gene clusters in nonpathogenic Pseudomonas genomes, covering 13 chemically diversified families. This global assessment of lipopeptide production capacity revealed it to be confined to the Pseudomonas fluorescens lineage, with most strains synthesizing a single type of CLP. Whereas certain lipopeptide families are specific for a taxonomic subgroup, others are found in distant groups. NRPS activation domain-guided peptide predictions enabled reliable family assignments, including identification of novel members. Focusing on the two most abundant lipopeptide families (Viscosin and Amphisin), a portion of their uncharted diversity was mapped, including characterization of two novel Amphisin family members (nepenthesin and oakridgin). Using NMR fingerprint matching, known Viscosin-family lipopeptides were identified in 15 (type) species spread across different taxonomic groups. A bifurcate genomic organization predominates among Viscosin-family producers and typifies Xantholysin-, Entolysin-, and Poaeamide-family producers but most families feature a single NRPS gene cluster embedded between cognate regulator and transporter genes. The strong correlation observed between NRPS system phylogeny and rpoD-based taxonomic affiliation indicates that much of the structural diversity is linked to speciation, providing few indications of horizontal gene transfer. The grouping of most NRPS systems in four superfamilies based on activation domain homology suggests extensive module dynamics driven by domain deletions, duplications, and exchanges. IMPORTANCE Pseudomonas species are prominent producers of lipopeptides that support proliferation in a multitude of environments and foster varied lifestyles. By genome mining of biosynthetic gene clusters (BGCs) with lipopeptide-specific organization, we mapped the global Pseudomonas lipopeptidome and linked its staggering diversity to taxonomy of the producers, belonging to different groups within the major Pseudomonas fluorescens lineage. Activation domain phylogeny of newly mined lipopeptide synthetases combined with previously characterized enzymes enabled assignment of predicted BGC products to specific lipopeptide families. In addition, novel peptide sequences were detected, showing the value of substrate specificity analysis for prioritization of BGCs for further characterization. NMR fingerprint matching proved an excellent tool to unequivocally identify multiple lipopeptides bioinformatically assigned to the Viscosin family, by far the most abundant one in Pseudomonas and with stereochemistry of all its current members elucidated. In-depth analysis of activation domains provided insight into mechanisms driving lipopeptide structural diversification.

Ecological Niche-Inspired Genome Mining Leads to the Discovery of Crop-Protecting Nonribosomal Lipopeptides Featuring a Transient Amino Acid Building Block

Investigating the ecological context of microbial predator-prey interactions enables the identification of microorganisms, which produce multiple secondary metabolites to evade predation or to kill the predator. In addition, genome mining combined with molecular biology methods can be used to identify further biosynthetic gene clusters that yield new antimicrobials to fight the antimicrobial crisis. In contrast, classical screening-based approaches have limitations since they do not aim to unlock the entire biosynthetic potential of a given organism. Here, we describe the genomics-based identification of keanumycins A-C. These nonribosomal peptides enable bacteria of the genus Pseudomonas to evade amoebal predation. While being amoebicidal at a nanomolar level, these compounds also exhibit a strong antimycotic activity in particular against the devastating plant pathogen Botrytis cinerea and they drastically inhibit the infection of Hydrangea macrophylla leaves using only supernatants of Pseudomonas cultures. The structures of the keanumycins were fully elucidated through a combination of nuclear magnetic resonance, tandem mass spectrometry, and degradation experiments revealing an unprecedented terminal imine motif in keanumycin C extending the family of nonribosomal amino acids by a highly reactive building block. In addition, chemical synthesis unveiled the absolute configuration of the unusual dihydroxylated fatty acid of keanumycin A, which has not yet been reported for this lipodepsipeptide class. Finally, a detailed genome-wide microarray analysis of Candida albicans exposed to keanumycin A shed light on the mode-of-action of this potential natural product lead, which will aid the development of new pharmaceutical and agrochemical antifungals.

The Diversity of Lipopeptides in the Pseudomonas syringae Complex Parallels Phylogeny and Sheds Light on Structural Diversification during Evolutionary History

Pseudomonas spp. colonize diverse aquatic and terrestrial habitats and produce a wide variety of secondary metabolites, including lipopeptides. However, previous studies have often examined a limited number of lipopeptide-producing strains. In this study, we performed a systematic analysis of lipopeptide production across a wide data set of strains of the Pseudomonas syringae complex (724) by using a combined bioinformatics, mass spectrometry, and phylogenetics approach. The large P. syringae complex, which is composed of 13 phylogroups, is known to produce factins (including syringafactin-like lipopeptides), mycins (including syringomycin-like lipopeptides), and peptins (such as syringopeptins). We found that 80.8% of P. syringae strains produced lipopeptides and that factins were the most frequently produced (by 96% of the producing strains). P. syringae strains were either factin monoproducers or factin, mycin, and peptin coproducers or lipopeptide nonproducers in relation to their phylogenetic group. Our analyses led to the discovery of 42 new lipopeptides, bringing the number of lipopeptides identified in the P. syringae complex to 75. We also highlighted that factins have high structural resemblance and are widely distributed among the P. syringae complex, while mycins and peptins are highly structurally diverse and patchily distributed. IMPORTANCE This study provides an insight into the P. syringae metabolome that emphasizes the high diversity of lipopeptides produced within the P. syringae complex. The production profiles of strains are closely related to their phylogenetic classification, indicating that structural diversification of lipopeptides parallels the phylogeny of this bacterial complex, thereby further illustrating the inherent importance of lipopeptides in the ecology of this group of bacteria throughout its evolutionary history. Furthermore, this overview of P. syringae lipopeptides led us to propose a refined classification that could be extended to the lipopeptides produced by other bacterial groups.

Proof-Reading Thioesterase Boosts Activity of Engineered Nonribosomal Peptide Synthetase

Nonribosomal peptide synthetases (NRPSs) are a vast source of valuable natural products, and re-engineering them is an attractive path toward structurally diversified active compounds. NRPS engineering often requires heterologous expression, which is hindered by the enormous size of NRPS proteins. Protein splitting and docking domain insertion have been proposed as a strategy to overcome this limitation. Here, we have applied the splitting strategy to the gramicidin S NRPS: Despite better production of the split proteins, gramicidin S production almost ceased. However, the addition of type II thioesterase GrsT boosted production. GrsT is an enzyme encoded in the gramicidin S biosynthetic gene cluster that we have produced and characterized for this purpose. We attribute the activity enhancement to the removal of a stalled intermediate from the split NRPS that is formed due to misinitiation. These results highlight type II thioesterases as useful tools for NRPS engineering.

An Nuclear Magnetic Resonance Fingerprint Matching Approach for the Identification and Structural Re-Evaluation of Pseudomonas Lipopeptides

Cyclic lipopeptides (CLiPs) are secondary metabolites secreted by a range of bacterial phyla. CLiPs from Pseudomonas in particular, display diverse structural variations in terms of the number of amino acid residues, macrocycle size, amino acid identity, and stereochemistry (e.g., d- versus l-amino acids). Reports detailing the discovery of novel or already characterized CLiPs from new sources appear regularly in literature. Increasingly, however, the lack of detailed characterization threatens to cause considerable confusion, especially if configurational heterogeneity is present for one or more amino acids. Using Pseudomonas CLiPs from the Bananamide, Orfamide, and Xantholysin groups as test cases, we demonstrate and validate that the combined 1H and 13C Nuclear Magnetic Resonance (NMR) chemical shifts of CLiPs constitute a spectral fingerprint that is sufficiently sensitive to differentiate between possible diastereomers of a particular sequence even when they only differ in a single d/l configuration. Rapid screening, involving simple matching of the NMR fingerprint of a newly isolated CLiP with that of a reference CLiP of known stereochemistry, can then be applied to resolve dead-ends in configurational characterization and avoid the much more cumbersome chemical characterization protocols. Even when the stereochemistry of a particular reference CLiP remains to be established, its spectral fingerprint allows to quickly verify whether a newly isolated CLiP is novel or already present in the reference collection. We show NMR fingerprinting leads to a simple approach for early on dereplication which should become more effective as more fingerprints are collected. To benefit research involving CLiPs, we have made a publicly available data repository accompanied by a 'knowledge base' at https://www.rhizoclip.be, where we present an overview of published NMR fingerprint data of characterized CLiPs, together with literature data on the originally determined structures. IMPORTANCE Pseudomonas CLiPs are ubiquitous specialized metabolites, impacting the producer's lifestyle and interactions with the (a)biotic environment. Consequently, they generate interest for agricultural and clinical applications. Establishing structure-activity relationships as a premise to their development is hindered because full structural characterization including stereochemical information requires labor-intensive analyses, without guarantee for success. Moreover, increasing use of superficial comparison with previously characterized CLiPs introduces or propagates erroneous attributions, clouding further scientific progress. We provide a generally applicable characterization methodology based on matching NMR spectral fingerprints of newly isolated CLiPs to natural and synthetic reference compounds with (un)known stereochemistry. In addition, NMR fingerprinting is shown to provide a suitable basis for structural dereplication. A publicly available reference compound repository promises to facilitate participation of the lipopeptide research community in structural assessment and dereplication of newly isolated CLiPs, which should also support further developments in genome mining for novel CLiPs.

Recent research progress of biologically active peptides

With the rapid development of molecular biology and biochemical technology, great progress has been made in the study of peptides. Peptides are easy to digest and absorb, with lowering of blood pressure and cholesterol, improving immunity, regulating hormones, antibacterial, and antiviral effects. Peptides also have physiological regulation and biological metabolism functions with applications in the fields of feed production and biomedical research. In the future, the research focus of bioactive peptides will focus on their efficient preparation and application. This article introduces a comprehensive review of the types, synthesis, functionalization, and bio-related applications of bioactive peptides. For this aim, we introduced in detail various biopeptides and then presented the production methods of bioactive peptides, such as enzymatic synthesis, microbial fermentation, chemical synthesis, and others. The applications of bioactive peptides for anticancers, immune therapy, antibacterial, and other applications have been introduced and discussed. And discussed the development prospects of biologically active peptides.

Gene editing enables rapid engineering of complex antibiotic assembly lines

Re-engineering biosynthetic assembly lines, including nonribosomal peptide synthetases (NRPS) and related megasynthase enzymes, is a powerful route to new antibiotics and other bioactive natural products that are too complex for chemical synthesis. However, engineering megasynthases is very challenging using current methods. Here, we describe how CRISPR-Cas9 gene editing can be exploited to rapidly engineer one of the most complex megasynthase assembly lines in nature, the 2.0 MDa NRPS enzymes that deliver the lipopeptide antibiotic enduracidin. Gene editing was used to exchange subdomains within the NRPS, altering substrate selectivity, leading to ten new lipopeptide variants in good yields. In contrast, attempts to engineer the same NRPS using a conventional homologous recombination-mediated gene knockout and complementation approach resulted in only traces of new enduracidin variants. In addition to exchanging subdomains within the enduracidin NRPS, subdomains from a range of NRPS enzymes of diverse bacterial origins were also successfully utilized.

Pan-genome analysis identifies intersecting roles for Pseudomonas specialized metabolites in potato pathogen inhibition

Agricultural soil harbors a diverse microbiome that can form beneficial relationships with plants, including the inhibition of plant pathogens. Pseudomonas spp. are one of the most abundant bacterial genera in the soil and rhizosphere and play important roles in promoting plant health. However, the genetic determinants of this beneficial activity are only partially understood. Here, we genetically and phenotypically characterize the Pseudomonas fluorescens population in a commercial potato field, where we identify strong correlations between specialized metabolite biosynthesis and antagonism of the potato pathogens Streptomyces scabies and Phytophthora infestans. Genetic and chemical analyses identified hydrogen cyanide and cyclic lipopeptides as key specialized metabolites associated with S. scabies inhibition, which was supported by in planta biocontrol experiments. We show that a single potato field contains a hugely diverse and dynamic population of Pseudomonas bacteria, whose capacity to produce specialized metabolites is shaped both by plant colonization and defined environmental inputs.

Potato scab and blight are two major diseases which can cause heavy crop losses. They are caused, respectively, by the bacterium Streptomyces scabies and an oomycete (a fungus-like organism) known as Phytophthora infestans.

Fighting these disease-causing microorganisms can involve crop management techniques – for example, ensuring that a field is well irrigated helps to keep S. scabies at bay. Harnessing biological control agents can also offer ways to control disease while respecting the environment. Biocontrol bacteria, such as Pseudomonas, can produce compounds that keep S. scabies and P. infestans in check. However, the identity of these molecules and how irrigation can influence Pseudomonas population remains unknown.

To examine these questions, Pacheco-Moreno et al. sampled and isolated hundreds of Pseudomonas strains from a commercial potato field, closely examining the genomes of 69 of these. Comparing the genetic information of strains based on whether they could control the growth of S. scabies revealed that compounds known as cyclic lipopeptides are key to controlling the growth of S. scabies and P. infestans. Whether the field was irrigated also had a large impact on the strains forming the Pseudomonas population.

Working out how Pseudomonas bacteria block disease could speed up the search for biological control agents. The approach developed by Pacheco-Moreno et al. could help to predict which strains might be most effective based on their genetic features. Similar experiments could also work for other combinations of plants and diseases.

Transporter Gene-mediated Typing for Detection and Genome Mining of Lipopeptide-producing Pseudomonas

Pseudomonas lipopeptides (LPs) are involved in diverse ecological functions and have biotechnological application potential associated with their antimicrobial and/or antiproliferative activities. They are synthesized by multimodular nonribosomal peptide synthetases which, together with transport and regulatory proteins, are encoded by large biosynthetic gene clusters (BGCs). These secondary metabolites are classified in distinct families based on the sequence and length of the oligopeptide and size of the macrocycle, if present. The phylogeny of PleB, the MacB-like transporter that is part of a dedicated ATP-dependent tripartite efflux system driving export of Pseudomonas LPs, revealed a strong correlation with LP chemical diversity. As each LP BGC carries its cognate pleB, PleB is suitable as a diagnostic sequence for genome mining, allowing assignment of the putative metabolite to a particular LP family. In addition, pleB proved to be a suitable target gene for an alternative PCR method for detecting LP-producing Pseudomonas sp. and did not rely on amplification of catalytic domains of the biosynthetic enzymes. Combined with amplicon sequencing, this approach enabled typing of Pseudomonas strains as potential producers of a LP belonging to one of the known LP families, underscoring its value for strain prioritization. This finding was validated by chemical characterization of known LPs from three different families secreted by novel producers isolated from the rice or maize rhizosphere, namely, the type strains of Pseudomonas fulva (putisolvin), Pseudomonas zeae (tensin), and Pseudomonas xantholysinigenes (xantholysin). In addition, a new member of the Bananamide family, prosekin, was discovered in the type strain of Pseudomonas prosekii, which is an Antarctic isolate.

IMPORTANCEPseudomonas spp. are ubiquitous bacteria able to thrive in a wide range of ecological niches, and lipopeptides often support their lifestyle but also their interaction with other micro- and macro-organisms. Therefore, the production of lipopeptides is widespread among Pseudomonas strains. Consequently, Pseudomonas lipopeptide research not only affects chemists and microbiologists but also touches a much broader audience, including biochemists, ecologists, and plant biologists. In this study, we present a reliable transporter gene-guided approach for the detection and/or typing of Pseudomonas lipopeptide producers. Indeed, it allows us to readily assess the lipopeptide diversity among sets of Pseudomonas isolates and differentiate strains likely to produce known lipopeptides from producers of potentially novel lipopeptides. This work provides a valuable tool that can also be integrated in a genome mining strategy and adapted for the typing of other specialized metabolites.

Top-down synthetic biology approach for titer improvement of clinically important antibiotic daptomycin in Streptomyces roseosporus

Secondary metabolites are produced at low titers by native producers due to tight regulations of their productions in response to environmental conditions. Synthetic biology provides a rational engineering principle for transcriptional optimization of secondary metabolite BGCs (biosynthetic gene clusters). Here, we demonstrate the use of synthetic biology principles for the development of a high-titer strain of the clinically important antibiotic daptomycin. Due to the presence of large NRPS (non-ribosomal peptide synthetase) genes with multiple direct repeats, we employed a top-down approach that allows transcriptional optimization of genes in daptomycin BGC with the minimum inputs of synthetic DNAs. The repeat-free daptomycin BGC was created through partial codon-reprogramming of a NRPS gene and cloned into a shuttle BAC vector, allowing BGC refactoring in a host with a powerful recombination system. Then, transcriptions of functionally divided operons were sequentially optimized through three rounds of DBTL (design-build-test-learn) cycles that resulted in up to ~2300% improvement in total lipopeptide titers compared to the wild-type strain. Upon decanoic acid feeding, daptomycin accounted for ∼ 40% of total lipopeptide production. To the best of our knowledge, this is the highest improvement of daptomycin titer ever achieved through genetic engineering of S. roseosporus. The top-down engineering approach we describe here could be used as a general strategy for the development of high-titer industrial strains of secondary metabolites produced by BGCs containing genes of large multi-modular NRPS and PKS enzymes.

The Landscape of Recombination Events That Create Nonribosomal Peptide Diversity

Nonribosomal peptides (NRP) are crucial molecular mediators in microbial ecology and provide indispensable drugs. Nevertheless, the evolution of the flexible biosynthetic machineries that correlates with the stunning structural diversity of NRPs is poorly understood. Here, we show that recombination is a key driver in the evolution of bacterial NRP synthetase (NRPS) genes across distant bacterial phyla, which has guided structural diversification in a plethora of NRP families by extensive mixing and matching of biosynthesis genes. The systematic dissection of a large number of individual recombination events did not only unveil a striking plurality in the nature and origin of the exchange units but allowed the deduction of overarching principles that enable the efficient exchange of adenylation (A) domain substrates while keeping the functionality of the dynamic multienzyme complexes. In the majority of cases, recombination events have targeted variable portions of the Acore domains, yet domain interfaces and the flexible Asub domain remained untapped. Our results strongly contradict the widespread assumption that adenylation and condensation (C) domains coevolve and significantly challenge the attributed role of C domains as stringent selectivity filter during NRP synthesis. Moreover, they teach valuable lessons on the choice of natural exchange units in the evolution of NRPS diversity, which may guide future engineering approaches.

Discovery of Thanafactin A, a Linear, Proline-Containing Octalipopeptide from Pseudomonas sp. SH-C52, Motivated by Genome Mining

Genome mining of the bacterial strains Pseudomonas sp. SH-C52 and Pseudomonas fluorescens DSM 11579 showed that both strains contained a highly similar gene cluster encoding an octamodular nonribosomal peptide synthetase (NRPS) system which was not associated with a known secondary metabolite. Insertional mutagenesis of an NRPS component followed by comparative profiling led to the discovery of the corresponding novel linear octalipopeptide thanafactin A, which was subsequently isolated and its structure determined by two-dimensional NMR and further spectroscopic and chromatographic methods. In bioassays, thanafactin A exhibited weak protease inhibitory activity and was found to modulate swarming motility in a strain-specific manner.

Efficient rational modification of non-ribosomal peptides by adenylation domain substitution

Non-ribosomal peptide synthetase (NRPS) enzymes form modular assembly-lines, wherein each module governs the incorporation of a specific monomer into a short peptide product. Modules are comprised of one or more key domains, including adenylation (A) domains, which recognise and activate the monomer substrate; condensation (C) domains, which catalyse amide bond formation; and thiolation (T) domains, which shuttle reaction intermediates between catalytic domains. This arrangement offers prospects for rational peptide modification via substitution of substrate-specifying domains. For over 20 years, it has been considered that C domains play key roles in proof-reading the substrate; a presumption that has greatly complicated rational NRPS redesign. Here we present evidence from both directed and natural evolution studies that any substrate-specifying role for C domains is likely to be the exception rather than the rule, and that novel non-ribosomal peptides can be generated by substitution of A domains alone. We identify permissive A domain recombination boundaries and show that these allow us to efficiently generate modified pyoverdine peptides at high yields. We further demonstrate the transferability of our approach in the PheATE-ProCAT model system originally used to infer C domain substrate specificity, generating modified dipeptide products at yields that are inconsistent with the prevailing dogma.

Lipopeptide families at the interface between pathogenic and beneficial Pseudomonas-plant interactions

Lipopeptides (LPs) are a prominent class of molecules among the steadily growing spectrum of specialized metabolites retrieved from Pseudomonas, in particular soil-dwelling and plant-associated isolates. Among the multiple LP families, pioneering research focussed on phytotoxic and antimicrobial cyclic lipopeptides (CLPs) of the ubiquitous plant pathogen Pseudomonas syringae (syringomycin and syringopeptin). Their non-ribosomal peptide synthetases (NRPSs) are embedded in biosynthetic gene clusters (BGCs) that are tightly co-clustered on a pathogenicity island. Other members of the P. syringae group (Pseudomonas cichorii) and some species of the Pseudomonas asplenii group and Pseudomonas fluorescens complex have adopted these biosynthetic strategies to co-produce their own mycin and peptin variants, in some strains supplemented with an analogue of the P. syringae linear LP (LLP), syringafactin. This capacity is not confined to phytopathogens but also occurs in some biocontrol strains, which indicates that these LP families not solely function as general virulence factors. We address this issue by scrutinizing the structural diversity and bioactivities of LPs from the mycin, peptin, and factin families in a phylogenetic and evolutionary perspective. BGC functional organization (including associated regulatory and transport genes) and NRPS modular architectures in known and candidate LP producers were assessed by genome mining.

Structure elucidation of bacterial nonribosomal lipopeptides

We provide a summary of the tools, which allow elucidate the structures of nonribosomal lipopetides.