Genomics of sponge-associated Streptomyces spp. closely related to Streptomyces albus J1074: insights into marine adaptation and secondary metabolite biosynthesis potential

Systems metabolic engineering of the primary and secondary metabolism of Streptomyces albidoflavus enhances production of the reverse antibiotic nybomycin against multi-resistant Staphylococcus aureus

Nybomycin is an antibiotic compound with proven activity against multi-resistant Staphylococcus aureus, making it an interesting candidate for combating these globally threatening pathogens. For exploring its potential, sufficient amounts of nybomycin and its derivatives must be synthetized to fully study its effectiveness, safety profile, and clinical applications. As native isolates only accumulate low amounts of the compound, superior producers are needed. The heterologous cell factory S. albidoflavus 4N24, previously derived from the cluster-free chassis S. albidoflavus Del14, produced 860 μg L-1 of nybomycin, mainly in the stationary phase. A first round of strain development modulated expression of genes involved in supply of nybomycin precursors under control of the common Perm* promoter in 4N24, but without any effect. Subsequent studies with mCherry reporter strains revealed that Perm* failed to drive expression during the product synthesis phase but that use of two synthetic promoters (PkasOP* and P41) enabled strong constitutive expression during the entire process. Using PkasOP*, several rounds of metabolic engineering successively streamlined expression of genes involved in the pentose phosphate pathway, the shikimic acid pathway, supply of CoA esters, and nybomycin biosynthesis and export, which more than doubled the nybomycin titer to 1.7 mg L-1 in the sixth-generation strain NYB-6B. In addition, we identified the minimal set of nyb genes needed to synthetize the molecule using single-gene-deletion strains. Subsequently, deletion of the regulator nybW enabled nybomycin production to begin during the growth phase, further boosting the titer and productivity. Based on RNA sequencing along the created strain genealogy, we discovered that the nyb gene cluster was unfavorably downregulated in all advanced producers. This inspired removal of a part and the entire set of the four regulatory genes at the 3'-end nyb of the cluster. The corresponding mutants NYB-8 and NYB-9 exhibited marked further improvement in production, and the deregulated cluster was combined with all beneficial targets from primary metabolism. The best strain, S. albidoflavus NYB-11, accumulated up to 12 mg L-1 nybomycin, fifteenfold more than the basic strain. The absence of native gene clusters in the host and use of a lean minimal medium contributed to a selective production process, providing an important next step toward further development of nybomycin.

Bioprospecting of unexplored halophilic actinobacteria against human infectious pathogens

Human pathogenic diseases received much attention recently due to their uncontrolled spread of antimicrobial resistance (AMR) which causes several threads every year. Effective alternate antimicrobials are urgently required to combat those disease causing infectious microbes. Halophilic actinobacteria revealed huge potentials and unexplored cultivable/non-cultivable actinobacterial species producing enormous antimicrobials have been proved in several genomics approaches. Potential gene clusters, PKS and NRPKS from Nocardia, Salinospora, Rhodococcus, and Streptomyces have wide range coding genes of secondary metabolites. Biosynthetic pathways identification via various approaches like genome mining, In silico, OSMAC (one strain many compound) analysis provides better identification of knowing the active metabolites using several databases like AMP, APD and CRAMPR, etc. Genome constellations of actinobacteria particularly the prediction of BGCs (Biosynthetic Gene Clusters) to mine the bioactive molecules such as pigments, biosurfactants and few enzymes have been reported for antimicrobial activity. Saltpan, saltlake, lagoon and haloalkali environment exploring potential actinobacterial strains Micromonospora, Kocuria, Pseudonocardia, and Nocardiopsis revealed several acids and ester derivatives with antimicrobial potential. Marine sediments and marine macro organisms have been found as significant population holders of potential actinobacterial strains. Deadly infectious diseases (IDs) including tuberculosis, ventilator-associated pneumonia and Candidiasis, have been targeted by halo-actinobacterial metabolites with promising results. Methicillin resistant Staphylococus aureus and virus like Encephalitic alphaviruses were potentially targeted by halophilic actinobacterial metabolites by the compound Homoseongomycin from sponge associated antinobacterium. In this review, we discuss the potential antimicrobial properties of various biomolecules extracted from the unexplored halophilic actinobacterial strains specifically against human infectious pathogens along with prospective genomic constellations.

Diversity of Bacterial Secondary Metabolite Biosynthetic Gene Clusters in Three Vietnamese Sponges

Recent reviews have reinforced sponge-associated bacteria as a valuable source of structurally diverse secondary metabolites with potent biological properties, which makes these microbial communities promising sources of new drug candidates. However, the overall diversity of secondary metabolite biosynthetic potential present in bacteria is difficult to access due to the fact that the majority of bacteria are not readily cultured in the laboratory. Thus, use of cultivation-independent approaches may allow accessing "silent" and "cryptic" secondary metabolite biosynthetic gene clusters present in bacteria that cannot yet be cultured. In the present study, we investigated the diversity of secondary metabolite biosynthetic gene clusters (BGCs) in metagenomes of bacterial communities associated with three sponge species: Clathria reinwardti, Rhabdastrella globostellata, and Spheciospongia sp. The results reveal that the three metagenomes contain a high number of predicted BGCs, ranging from 282 to 463 BGCs per metagenome. The types of BGCs were diverse and represented 12 different cluster types. Clusters predicted to encode fatty acid synthases and polyketide synthases (PKS) were the most dominant BGC types, followed by clusters encoding synthesis of terpenes and bacteriocins. Based on BGC sequence similarity analysis, 363 gene cluster families (GCFs) were identified. Interestingly, no GCFs were assigned to pathways responsible for the production of known compounds, implying that the clusters detected might be responsible for production of several novel compounds. The KS gene sequences from PKS clusters were used to predict the taxonomic origin of the clusters involved. The KS sequences were related to 12 bacterial phyla with Actinobacteria, Proteobacteria, and Firmicutes as the most predominant. At the genus level, the KSs were most related to those found in the genera Mycolicibacterium, Mycobacterium, Burkholderia, and Streptomyces. Phylogenetic analysis of KS sequences resulted in detection of two known 'sponge-specific' BGCs, i.e., SupA and SwfA, as well as a new 'sponge-specific' cluster related to fatty acid synthesis in the phylum Candidatus Poribacteria and composed only by KS sequences of the three sponge-associated bacterial communities assessed here.

Isolation and Identification of Bioactive Compounds from Streptomyces actinomycinicus PJ85 and Their In Vitro Antimicrobial Activities against Methicillin-Resistant Staphylococcus aureus

Antibiotic-resistant strains are a global health-threatening problem. Drug-resistant microbes have compromised the control of infectious diseases. Therefore, the search for a novel class of antibiotic drugs is necessary. Streptomycetes have been described as the richest source of bioactive compounds, including antibiotics. This study was aimed to characterize the antibacterial compounds of Streptomyces sp. PJ85 isolated from dry dipterocarp forest soil in Northeast Thailand. The 16S rRNA gene sequence and phylogenetic analysis showed that PJ85 possessed a high similarity to Streptomyces actinomycinicus RCU-197^T of 98.90%. The PJ85 strain was shown to produce antibacterial compounds that were active against Gram-positive bacteria including methicillin-resistant Staphylococcus aureus (MRSA). The active compounds of PJ85 were extracted and purified using silica gel column chromatography. Two active antibacterial compounds, compound 1 and compound PJ85_F39, were purified and characterized with spectroscopy, including liquid chromatography and mass spectrometry (LC-MS). Compound 1 was identified as actinomycin D, and compound PJ85_F39 was identified as dihomo-γ-linolenic acid (DGLA). To the best of our knowledge, this is the first report of the purification and characterization of the antibacterial compounds of S. actinomycinicus.

Spiractinospora alimapuensis gen. nov., sp. nov., isolated from marine sediment of Valparaíso Bay (Chile) and proposal for reclassification of two species of the genus Nocardiopsis

An alkaliphilic actinobacterium, designated VN6-2T, was isolated from marine sediment collected from Valparaíso Bay, Chile. Strain VN6-2T formed yellowish-white branched substrate mycelium without fragmentation. Aerial mycelium was well developed, forming wavy or spiral spore chains. Strain VN6-2T exhibited a 16S rRNA gene sequence similarity of 93.9 % to Salinactinospora qingdaonensis CXB832T, 93.7 % to Murinocardiopsis flavida 14-Be-013T, and 93.7 % to Lipingzhangella halophila 14-Be-013T. Genome sequencing revealed a genome size of 5.9 Mb and an in silico G+C content of 69.3 mol%. Both of the phylogenetic analyses based on 16S rRNA gene sequences and the up-to-date bacterial core gene sequences revealed that strain VN6-2T formed a distinct monophyletic clade within the family Nocardiopsaceae . Chemotaxonomic assessment of strain VN6-2T showed that the major fatty acids were iso-C16 : 0, anteiso-C17 : 0 and 10-methyl-C18 : 0, and the predominant respiratory quinones were MK-9, MK-9(H2) and MK-9(H4). Whole-cell hydrolysates contained meso-diaminopimelic acid as the cell-wall diamino acid, and ribose and xylose as the diagnostic sugars. The polar lipid profile consisted of diphosphatidylglycerol, phosphatidylglycerol, phosphatidylcholine, aminophospholipids, glycolipid and phospholipid. Based on the results of this polyphasic study, a novel genus, Spiractinospora gen. nov., is proposed within the family Nocardiopsaceae and the type species Spiractinospora alimapuensis gen. nov., sp. nov. The type strain is VN6-2T (CECT 30026T, CCUG 66258T). On the basis of the phylogenetic results herein, we also propose that Nocardiopsis arvandica and Nocardiopsis litoralis are later heterotypic synonyms of Nocardiopsis sinuspersici and Nocardiopsis kunsanensis , respectively, for which emended descriptions are given.

Pharmacological Properties, Volatile Organic Compounds, and Genome Sequences of Bacterial Endophytes from the Mangrove Plant Rhizophora apiculata Blume

Mangrove plant endophytic bacteria are prolific sources of bioactive secondary metabolites. In the present study, twenty-three endophytic bacteria were isolated from the fresh roots of the mangrove plant Rhizophora apiculata. The identification of isolates by 16S rRNA gene sequences revealed that the isolated endophytic bacteria belonged to nine genera, including Streptomyces, Bacillus, Pseudovibrio, Microbacterium, Brevibacterium, Microbulbifer, Micrococcus, Rossellomorea, and Paracoccus. The ethyl acetate extracts of the endophytic bacteria’s pharmacological properties were evaluated in vitro, including antimicrobial, antioxidant, α-amylase and α-glucosidase inhibitory, xanthine oxidase inhibitory, and cytotoxic activities. Gas chromatography–mass spectrometry (GC-MS) analyses of three high bioactive strains Bacillus sp. RAR_GA_16, Rossellomorea vietnamensis RAR_WA_32, and Bacillus sp. RAR_M1_44 identified major volatile organic compounds (VOCs) in their ethyl acetate extracts. Genome analyses identified biosynthesis gene clusters (BGCs) of secondary metabolites of the bacterial endophytes. The obtained results reveal that the endophytic bacteria from R. apiculata may be a potential source of pharmacological secondary metabolites, and further investigations of the high bioactive strains—such as fermentation and isolation of pure bioactive compounds, and heterologous expression of novel BGCs in appropriate expression hosts—may allow exploring and exploiting the promising bioactive compounds for future drug development.

Complete Genome Sequence of Two Deep-Sea Streptomyces Isolates from Madeira Archipelago and Evaluation of Their Biosynthetic Potential

The deep-sea constitutes a true unexplored frontier and a potential source of innovative drug scaffolds. Here, we present the genome sequence of two novel marine actinobacterial strains, MA3_2.13 and S07_1.15, isolated from deep-sea samples (sediments and sponge) and collected at Madeira archipelago (NE Atlantic Ocean; Portugal). The de novo assembly of both genomes was achieved using a hybrid strategy that combines short-reads (Illumina) and long-reads (PacBio) sequencing data. Phylogenetic analyses showed that strain MA3_2.13 is a new species of the Streptomyces genus, whereas strain S07_1.15 is closely related to the type strain of Streptomyces xinghaiensis. In silico analysis revealed that the total length of predicted biosynthetic gene clusters (BGCs) accounted for a high percentage of the MA3_2.13 genome, with several potential new metabolites identified. Strain S07_1.15 had, with a few exceptions, a predicted metabolic profile similar to S. xinghaiensis. In this work, we implemented a straightforward approach for generating high-quality genomes of new bacterial isolates and analyse in silico their potential to produce novel NPs. The inclusion of these in silico dereplication steps allows to minimize the rediscovery rates of traditional natural products screening methodologies and expedite the drug discovery process.

Streptomyces poriferorum sp. nov., a novel marine sponge-derived Actinobacteria species expressing anti-MRSA activity

Marine sponges represent a rich source of uncharacterized microbial diversity, and many are host to microorganisms that produce biologically active specialized metabolites. Here, a polyphasic approach was used to characterize two Actinobacteria strains, P01-B04^T and P01-F02, that were isolated from the marine sponges Geodia barretti (Bowerbank, 1858) and Antho dichotoma (Esper, 1794), respectively. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strains P01-B04^T and P01-F02 are closely related to Streptomyces beijiangensis DSM 41794^T, Streptomyces laculatispora NRRL B-24909^T, and Streptomyces brevispora NRRL B-24910^T. The two strains showed nearly identical 16S rRNA gene sequences (99.93%), and the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) relatedness values were 99.96% and 99.6%, respectively, suggesting that these strains are affiliated with the same species. Chemotaxonomic and culture characteristics of both strains were also consistent with the genus Streptomyces, while phenotypic properties, genome-based comparisons, and phylogenomic analyses distinguished strains P01-B04^T and P01-F02 from their closest phylogenetic relatives. In silico analysis predicted that the 8.9 Mb genome of P01-B04^T contains at least 41 biosynthetic gene clusters (BGCs) encoding secondary metabolites, indicating that this strain could express diverse bioactive metabolites; in support of this prediction, this strain expressed antibacterial activity against Gram-positive bacteria including a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA) EAMC30. Based on these results, the marine sponge-associated isolates represent a novel species of the genus Streptomyces, for which the name Streptomyces poriferorum sp. nov. is proposed, with P01-B04^T (=DSM 111306^T = CCM 9048^T) as the type strain.

The Genome Analysis of the Human Lung-Associated Streptomyces sp. TR1341 Revealed the Presence of Beneficial Genes for Opportunistic Colonization of Human Tissues

Streptomyces sp. TR1341 was isolated from the sputum of a man with a history of lung and kidney tuberculosis, recurrent respiratory infections, and COPD. It produces secondary metabolites associated with cytotoxicity and immune response modulation. In this study, we complement our previous results by identifying the genetic features associated with the production of these secondary metabolites and other characteristics that could benefit the strain during its colonization of human tissues (virulence factors, modification of the host immune response, or the production of siderophores). We performed a comparative phylogenetic analysis to identify the genetic features that are shared by environmental isolates and human respiratory pathogens. The results showed a high genomic similarity of Streptomyces sp. TR1341 to the plant-associated Streptomyces sp. endophyte_N2, inferring a soil origin of the strain. Putative virulence genes, such as mammalian cell entry (mce) genes were not detected in the TR1341’s genome. The presence of a type VII secretion system, distinct from the ones found in Mycobacterium species, suggests a different colonization strategy than the one used by other actinomycete lung pathogens. We identified a higher diversity of genes related to iron acquisition and demonstrated that the strain produces ferrioxamine B in vitro. These results indicate that TR1341 may have an advantage in colonizing environments that are low in iron, such as human tissue.

Diversity and Antimicrobial Activity of Vietnamese Sponge-Associated Bacteria

This study aimed to assess the diversity and antimicrobial activity of cultivable bacteria associated with Vietnamese sponges. In total, 460 bacterial isolates were obtained from 18 marine sponges. Of these, 58.3% belonged to Proteobacteria, 16.5% to Actinobacteria, 18.0% to Firmicutes, and 7.2% to Bacteroidetes. At the genus level, isolated strains belonged to 55 genera, of which several genera, such as Bacillus, Pseudovibrio, Ruegeria, Vibrio, and Streptomyces, were the most predominant. Culture media influenced the cultivable bacterial composition, whereas, from different sponge species, similar cultivable bacteria were recovered. Interestingly, there was little overlap of bacterial composition associated with sponges when the taxa isolated were compared to cultivation-independent data. Subsequent antimicrobial assays showed that 90 isolated strains exhibited antimicrobial activity against at least one of seven indicator microorganisms. From the culture broth of the isolated strain with the strongest activity (Bacillus sp. M1_CRV_171), four secondary metabolites were isolated and identified, including cyclo(L-Pro-L-Tyr) (1), macrolactin A (2), macrolactin H (3), and 15,17-epoxy-16-hydroxy macrolactin A (4). Of these, compounds 2-4 exhibited antimicrobial activity against a broad spectrum of reference microorganisms.

Production and characterisation of a novel actinobacterial DyP-type peroxidase and its application in coupling of phenolic monomers

The extracellular peroxidase from Streptomyces albidoflavus BSII#1 was purified to near homogeneity using sequential steps of acid and acetone precipitation, followed by ultrafiltration. The purified peroxidase was characterised and tested for the ability to catalyse coupling reactions between selected phenolic monomer pairs. A 46-fold purification of the peroxidase was achieved, and it was shown to be a 46 kDa haem peroxidase. Unlike other actinobacteria-derived peroxidases, it was only inhibited (27 % inhibition) by relatively high concentrations of sodium azide (5 mM) and was capable of oxidising eleven (2,4-dichlorophenol, 2,6-dimethoxyphenol, 4-tert-butylcatechol, ABTS, caffeic acid, catechol, guaiacol, l-DOPA, o-aminophenol, phenol, pyrogallol) of the seventeen substrates tested. The peroxidase remained stable at temperatures of up to 80 °C for 60 min and retained >50 % activity after 24 h between pH 5.0-9.0, but was most sensitive to incubation with hydrogen peroxide (H₂O₂; 0.01 mM), l-cysteine (0.02 mM) and ascorbate (0.05 mM) for one hour. It was significantly inhibited by all organic solvents tested (p ≤ 0.05). The K_m and V_max values of the partially purified peroxidase with the substrate 2,4-DCP were 0.95 mM and 0.12 mmol min^-1, respectively. The dyes reactive blue 4, reactive black 5, and Azure B, were all decolourised to a certain extent: approximately 30 % decolourisation was observed after 24 h (1 μM dye). The peroxidase successfully catalysed coupling reactions between several phenolic monomer pairs including catechin-caffeic acid, catechin-catechol, catechin-guaiacol and guaiacol-syringaldazine under the non-optimised conditions used in this study. Genome sequencing confirmed the identity of strain BSII#1 as a S. albidoflavus strain. In addition, the genome sequence revealed the presence of one peroxidase gene that includes the twin arginine translocation signal sequence of extracellular proteins. Functional studies confirmed that the peroxidase produced by S. albidoflavus BSII#1 is part of the dye-decolourising peroxidase (DyP-type) family.

Streptomyces spp. From the Marine Sponge Antho dichotoma: Analyses of Secondary Metabolite Biosynthesis Gene Clusters and Some of Their Products

Actinomycete bacteria from marine environments represent a potential source for new antibiotics and anti-tumor drugs. Ten strains belonging to the genus Streptomyces isolated from the marine sponge Antho dichotoma collected at the bottom of the Trondheim fjord (Norway) were screened for antibiotic activity. Since only few isolates proved to be bioactive in the conditions tested, we decided to gain an insight into their biosynthetic potential using genome sequencing and analysis. Draft genomes were analyzed for the presence of secondary metabolite biosynthesis gene clusters (BGCs) using antiSMASH software. BGCs specifying both known and potentially novel secondary metabolites were identified, suggesting that these isolates might be sources for new bioactive compounds. The results of this analysis also implied horizontal transfer of several gene clusters between the studied isolates, which was especially evident for the lantibiotic- and thiopeptide-encoding BGCs. The latter implies the significance of particular secondary metabolites for the adaptation of Streptomyces to the spatially enclosed marine environments such as marine sponges. Two bioactive isolates, one showing activity against both yeast and Bacillus subtilis, and one only against yeast were analyzed in details, leading to the identification of cycloheximide, linearmycins, and echinomycins that are presumably responsible for the observed bioactivities.

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.

In silico Screening and Heterologous Expression of a Polyethylene Terephthalate Hydrolase (PETase)-Like Enzyme (SM14est) With Polycaprolactone (PCL)-Degrading Activity, From the Marine Sponge-Derived Strain Streptomyces sp. SM14

Plastics, such as the polyethylene terephthalate (PET), are widely used for various industrial applications, due to their physicochemical properties which are particularly useful in the packaging industry. However, due to improper plastic waste management and difficulties in recycling, post-consumer plastic waste has become a pressing issue for both the environment and for human health. Hence, novel technologies and methods of processing plastic waste are required to address these issues. Enzymatic-assisted hydrolysis of synthetic polymers has been proposed as a potentially more efficient and environment-friendly alternative to the currently employed methods. Recently, a number of PET hydrolases have been described, and in particular a PETase derived from Ideonella sakaiensis 201-F6 (IsPETase), which appears to be the most efficient and substrate-specific bacterial PET hydrolase enzyme discovered to date. In order to further investigate this class of PETase-like enzymes, we employed an in silico-based screening approach on the biotechnologically relevant genus Streptomyces, including terrestrial and marine isolates; in a search for potential PETase homologs. From a total of 52 genomes analyzed, we were able to identify three potential PETase-like enzymes, all of which were derived from marine-sponge associated Streptomyces isolates. A candidate PETase-like gene (SM14est) was identified in Streptomyces sp. SM14. Further in silico characterization of the SM14est protein sequence and its predicted three-dimensional structure were performed and compared to the well-characterized IsPETase. Both the serine hydrolase motif Gly-x1-Ser-x2-Gly and the catalytic triad Ser, Asp, His are conserved in both sequences. Molecular docking experiments indicated that the SM14est enzyme possessed the capacity to bind plastics as substrates. Finally, polyesterase activity was confirmed using a polycaprolactone (PCL) plate clearing assay which is a model substrate for the degradation of plastics; following heterologous expression of SM14est in Escherichia coli, with secretion being facilitated by the native Streptomyces signal peptide. These findings provide further insights into this important class of PETase-like enzymes.

Novel bioactive natural products from bacteria via bioprospecting, genome mining and metabolic engineering

For over seven decades, bacteria served as a valuable source of bioactive natural products some of which were eventually developed into drugs to treat infections, cancer and immune system-related diseases. Traditionally, novel compounds produced by bacteria were discovered via conventional bioprospecting based on isolation of potential producers and screening their extracts in a variety of bioassays. Over time, most of the natural products identifiable by this approach were discovered, and the pipeline for new drugs based on bacterially produced metabolites started to run dry. This mini-review highlights recent developments in bacterial bioprospecting for novel compounds that are based on several out-of-the-box approaches, including the following: (i) targeting bacterial species previously unknown to produce any bioactive natural products, (ii) exploring non-traditional environmental niches and methods for isolation of bacteria and (iii) various types of 'genome mining' aimed at unravelling genetic potential of bacteria to produce secondary metabolites. All these approaches have already yielded a number of novel bioactive compounds and, if used wisely, will soon revitalize drug discovery pipeline based on bacterial natural products.

Comparative Genomic Insights into Secondary Metabolism Biosynthetic Gene Cluster Distributions of Marine Streptomyces

Bacterial secondary metabolites have huge application potential in multiple industries. Biosynthesis of bacterial secondary metabolites are commonly encoded in a set of genes that are organized in the secondary metabolism biosynthetic gene clusters (SMBGCs). The development of genome sequencing technology facilitates mining bacterial SMBGCs. Marine Streptomyces is a valuable resource of bacterial secondary metabolites. In this study, 87 marine Streptomyces genomes were obtained and carried out into comparative genomic analysis, which revealed their high genetic diversity due to pan-genomes owning 123,302 orthologous clusters. Phylogenomic analysis indicated that the majority of Marine Streptomyces were classified into three clades named Clade I, II, and III, containing 23, 38, and 22 strains, respectively. Genomic annotations revealed that SMBGCs in the genomes of marine Streptomyces ranged from 16 to 84. Statistical analysis pointed out that phylotypes and ecotypes were both associated with SMBGCs distribution patterns. The Clade I and marine sediment-derived Streptomyces harbored more specific SMBGCs, which consisted of several common ones; whereas the Clade II and marine invertebrate-derived Streptomyces have more SMBGCs, acting as more plentiful resources for mining secondary metabolites. This study is beneficial for broadening our knowledge about SMBGC distribution patterns in marine Streptomyces and developing their secondary metabolites in the future.

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.

Population Genomics Insights into Adaptive Evolution and Ecological Differentiation in Streptomycetes

Deciphering the genomic variation that represents microevolutionary processes toward species divergence is key to understanding microbial speciation, which has long been under debate. Streptomycetes are filamentous bacteria that are ubiquitous in nature and the richest source of antibiotics; however, their speciation processes remain unknown. To tackle this issue, we performed a comprehensive population genomics analysis on Streptomyces albidoflavus residing in different habitats and with a worldwide distribution and identified and characterized the foundational changes within the species. We detected three well-defined phylogenomic clades, of which clades I and III mainly contained free-living (soil/marine) and insect-associated strains, respectively, and clade II had a mixed origin. By performing genome-wide association studies (GWAS), we identified a number of genetic variants associated with free-living or entomic (denoting or relating to insects) habitats in both the accessory and core genomes. These variants contributed collectively to the population structure and had annotated or confirmed functions that likely facilitate differential adaptation of the species. In addition, we detected higher levels of homologous recombination within each clade and in the free-living group than within the whole species and in the entomic group. A subset of the insect-associated strains (clade III) showed a relatively independent evolutionary trajectory with more symbiosis-favorable genes but little genetic interchange with the other lineages. Our results demonstrate that ecological adaptation promotes genetic differentiation in S. albidoflavus, suggesting a model of ecological speciation with gene flow in streptomycetes.IMPORTANCE Species are the fundamental units of ecology and evolution, and speciation leads to the astounding diversity of life on Earth. Studying speciation is thus of great significance to understand, protect, and exploit biodiversity, but it is a challenge in the microbial world. In this study, using population genomics, we placed Streptomyces albidoflavus strains in a spectrum of speciation and showed that the genetic differences between phylogenomic clusters evolved mainly by environmental selection and gene-specific sweeps. These findings highlight the role of ecology in structuring recombining bacterial species, making a step toward a deeper understanding of microbial speciation. Our results also raise concerns of an underrated microbial diversity at the intraspecies level, which can be utilized for mining of ecologically relevant natural products.

Analysis of the complete genome sequence of a marine-derived strain Streptomyces sp. S063 CGMCC 14582 reveals its biosynthetic potential to produce novel anti-complement agents and peptides

Genome sequences of marine streptomycetes are valuable for the discovery of useful enzymes and bioactive compounds by genome mining. However, publicly available complete genome sequences of marine streptomycetes are still limited. Here, we present the complete genome sequence of a marine streptomycete Streptomyces sp. S063 CGMCC 14582. Species delineation based on the pairwise digital DNA-DNA hybridization and genome comparison ANI (average nucleotide identity) value showed that Streptomyces sp. S063 CGMCC 14582 possesses a unique genome that is clearly different from all of the other available genomes. Bioactivity tests showed that Streptomyces sp. S063 CGMCC 14582 produces metabolites with anti-complement activities, which are useful for treatment of numerous diseases that arise from inappropriate activation of the human complement system. Analysis of the genome reveals no biosynthetic gene cluster (BGC) which shows even low similarity to that of the known anti-complement agents was detected in the genome, indicating that Streptomyces sp. S063 CGMCC 14582 may produce novel anti-complement agents of microbial origin. Four BGCs which are potentially involved in biosynthesis of non-ribosomal peptides were disrupted, but no decrease of anti-complement activities was observed, suggesting that these four BGCs are not involved in biosynthesis of the anti-complement agents. In addition, LC-MS/MS analysis and subsequent alignment through the Global Natural Products Social Molecular Networking (GNPS) platform led to the detection of novel peptides produced by the strain. Streptomyces sp. S063 CGMCC 14582 grows rapidly and is salt tolerant, which benefits efficient secondary metabolite production via seawater-based fermentation. Our results indicate that Streptomyces sp. S063 has great potential to produce novel bioactive compounds, and also is a good host for heterologous production of useful secondary metabolites 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.

Chitinolytic functions in actinobacteria: ecology, enzymes, and evolution

Actinobacteria, a large group of Gram-positive bacteria, secrete a wide range of extracellular enzymes involved in the degradation of organic compounds and biopolymers including the ubiquitous aminopolysaccharides chitin and chitosan. While chitinolytic enzymes are distributed in all kingdoms of life, actinobacteria are recognized as particularly good decomposers of chitinous material and several members of this taxon carry impressive sets of genes dedicated to chitin and chitosan degradation. Degradation of these polymers in actinobacteria is dependent on endo- and exo-acting hydrolases as well as lytic polysaccharide monooxygenases. Actinobacterial chitinases and chitosanases belong to nine major families of glycosyl hydrolases that share no sequence similarity. In this paper, the distribution of chitinolytic actinobacteria within different ecosystems is examined and their chitinolytic machinery is described and compared to those of other chitinolytic organisms.

Genome Mining of the Marine Actinomycete Streptomyces sp. DUT11 and Discovery of Tunicamycins as Anti-complement Agents

Marine actinobacteria are potential producers of various secondary metabolites with diverse bioactivities. Among various bioactive compounds, anti-complement agents have received great interest for drug discovery to treat numerous diseases caused by inappropriate activation of the human complement system. However, marine streptomycetes producing anti-complement agents are still poorly explored. In this study, a marine-derived strain Streptomyces sp. DUT11 showing superior anti-complement activity was focused, and its genome sequence was analyzed. Gene clusters showing high similarities to that of tunicamycin and nonactin were identified, and their corresponding metabolites were also detected. Subsequently, tunicamycin I, V, and VII were isolated from Streptomyces sp. DUT11. Anti-complement assay showed that tunicamycin I, V, VII inhibited complement activation through the classic pathway, whereas no anti-complement activity of nonactin was detected. This is the first time that tunicamycins are reported to have such activity. In addition, genome analysis indicates that Streptomyces sp. DUT11 has the potential to produce novel lassopeptides and lantibiotics. These results suggest that marine Streptomyces are rich sources of anti-complement agents for drug discovery.

Comparative Genomics Provides Insights Into the Marine Adaptation in Sponge-Derived Kocuriaflava S43

Sponge-derived actinomycetes represent a significant component of marine actinomycetes. Members of the genus Kocuria are distributed in various habitats such as soil, rhizosphere, clinical specimens, marine sediments, and sponges, however, to date, little is known about the mechanism of their environmental adaptation. Kocuria flava S43 was isolated from a coastal sponge. Phylogenetic analysis revealed that it was closely related to the terrestrial airborne K. flava HO-9041. In this study, to gain insights into the marine adaptation in K. flava S43 we sequenced the draft genome for K. flava S43 by third generation sequencing (TGS) and compared it with those of K. flava HO-9041 and some other Kocuria relatives. Comparative genomics and phylogenetic analyses revealed that K. flava S43 might adapt to the marine environment mainly by increasing the number of the genes linked to potassium homeostasis, resistance to heavy metals and phosphate metabolism, and acquiring the genes associated with electron transport and the genes encoding ATP-binding cassette (ABC) transporter, aquaporin, and thiol/disulfide interchange protein. Notably, gene acquisition was probably a primary mechanism of environmental adaptation in K. flava S43. Furthermore, this study also indicated that the Kocuria isolates from various marine and hyperosmotic environments possessed common genetic basis for environmental adaptation.

Diverse Cone-Snail Species Harbor Closely Related Streptomyces Species with Conserved Chemical and Genetic Profiles, Including Polycyclic Tetramic Acid Macrolactams

Streptomyces are Gram-positive bacteria that occupy diverse ecological niches including host-associations with animals and plants. Members of this genus are known for their overwhelming repertoire of natural products, which has been exploited for almost a century as a source of medicines and agrochemicals. Notwithstanding intense scientific and commercial interest in Streptomyces natural products, surprisingly little is known of the intra- and/or inter-species ecological roles played by these metabolites. In this report we describe the chemical structures, biological properties, and biosynthetic relationships between natural products produced by Streptomyces isolated from internal tissues of predatory Conus snails, collected from the Great Barrier Reef, Australia. Using chromatographic, spectroscopic and bioassays methodology, we demonstrate that Streptomyces isolated from five different Conus species produce identical chemical and antifungal profiles - comprising a suite of polycyclic tetramic acid macrolactams (PTMs). To investigate possible ecological (and evolutionary) relationships we used genome analyses to reveal a close taxonomic relationship with other sponge-derived and free-living PTM producing Streptomyces (i.e., Streptomyces albus). In-depth phylogenomic analysis of PTM biosynthetic gene clusters indicated PTM structure diversity was governed by a small repertoire of genetic elements, including discrete gene acquisition events involving dehydrogenases. Overall, our study shows a Streptomyces-Conus ecological relationship that is concomitant with specific PTM chemical profiles. We provide an evolutionary framework to explain this relationship, driven by anti-fungal properties that protect Conus snails from fungal pathogens.

Actinoalloteichus fjordicus sp. nov. isolated from marine sponges: phenotypic, chemotaxonomic and genomic characterisation

Two actinobacterial strains, ADI 127-17^T and GBA 129-24, isolated from marine sponges Antho dichotoma and Geodia barretti, respectively, collected at the Trondheim fjord in Norway, were the subjects of a polyphasic study. According to their 16S rRNA gene sequences, the new isolates were preliminarily classified as belonging to the genus Actinoalloteichus. Both strains formed a distinct branch, closely related to the type strains of Actinoalloteichus hoggarensis and Actinoalloteichus hymeniacidonis, within the evolutionary radiation of the genus Actinoalloteichus in the 16S rRNA gene-based phylogenetic tree. Isolates ADI 127-17^T and GBA 129-24 exhibited morphological, chemotaxonomic and genotypic features distinguishable from their close phylogenetic neighbours. Digital DNA: DNA hybridization and ANI values between strains ADI 127-17^T and GBA 129-24 were 97.6 and 99.7%, respectively, whereas the corresponding values between both tested strains and type strains of their closely related phylogenetic neighbours, A. hoggarensis and A. hymeniacidonis, were well below the threshold for delineation of prokaryotic species. Therefore, strains ADI 127-17^T (= DSM 46855^T) and GBA 129-24 (= DSM 46856) are concluded to represent a novel species of the genus Actinoalloteichus for which the name of Actinoalloteichus fjordicus sp. nov. (type strain ADI 127-17^T = DSM 46855^T = CECT 9355^T) is proposed. The complete genome sequences of the new strains were obtained and compared to that of A. hymeniacidonis DSM 45092^T and A. hoggarensis DSM 45943^T to unravel unique genome features and biosynthetic potential of the new isolates.

Recent advances in understanding Streptomyces

About 2,500 papers dated 2014–2016 were recovered by searching the PubMed database for Streptomyces, which are the richest known source of antibiotics. This review integrates around 100 of these papers in sections dealing with evolution, ecology, pathogenicity, growth and development, stress responses and secondary metabolism, gene expression, and technical advances. Genomic approaches have greatly accelerated progress. For example, it has been definitively shown that interspecies recombination of conserved genes has occurred during evolution, in addition to exchanges of some of the tens of thousands of non-conserved accessory genes. The closeness of the association of Streptomyces with plants, fungi, and insects has become clear and is reflected in the importance of regulators of cellulose and chitin utilisation in overall Streptomyces biology. Interestingly, endogenous cellulose-like glycans are also proving important in hyphal growth and in the clumping that affects industrial fermentations. Nucleotide secondary messengers, including cyclic di-GMP, have been shown to provide key input into developmental processes such as germination and reproductive growth, while late morphological changes during sporulation involve control by phosphorylation. The discovery that nitric oxide is produced endogenously puts a new face on speculative models in which regulatory Wbl proteins (peculiar to actinobacteria) respond to nitric oxide produced in stressful physiological transitions. Some dramatic insights have come from a new model system for Streptomyces developmental biology, Streptomyces venezuelae, including molecular evidence of very close interplay in each of two pairs of regulatory proteins. An extra dimension has been added to the many complexities of the regulation of secondary metabolism by findings of regulatory crosstalk within and between pathways, and even between species, mediated by end products. Among many outcomes from the application of chromosome immunoprecipitation sequencing (ChIP-seq) analysis and other methods based on “next-generation sequencing” has been the finding that 21% of Streptomyces mRNA species lack leader sequences and conventional ribosome binding sites. Further technical advances now emerging should lead to continued acceleration of knowledge, and more effective exploitation, of these astonishing and critically important organisms.

New Deferoxamine Glycoconjugates Produced upon Overexpression of Pathway-Specific Regulatory Gene in the Marine Sponge-Derived Streptomyces albus PVA94-07

Activation of silent biosynthetic gene clusters in Streptomyces bacteria via overexpression of cluster-specific regulatory genes is a promising strategy for the discovery of novel bioactive secondary metabolites. This approach was used in an attempt to activate a cryptic gene cluster in a marine sponge-derived Streptomyces albus PVA94-07 presumably governing the biosynthesis of peptide-based secondary metabolites. While no new peptide-based metabolites were detected in the recombinant strain, it was shown to produce at least four new analogues of deferoxamine with additional acyl and sugar moieties, for which chemical structures were fully elucidated. Biological activity tests of two of the new deferoxamine analogues revealed weak activity against Escherichia coli. The gene knockout experiment in the gene cluster targeted for activation, as well as overexpression of certain genes from this cluster did not have an effect on the production of these compounds by the strain overexpressing the regulator. It seems plausible that the production of such compounds is a response to stress imposed by the production of an as-yet unidentified metabolite specified by the cryptic cluster.

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.

Genetic manipulation of secondary metabolite biosynthesis for improved production in Streptomyces and other actinomycetes

Actinomycetes continue to be important sources for the discovery of secondary metabolites for applications in human medicine, animal health, and crop protection. With the maturation of actinomycete genome mining as a robust approach to identify new and novel cryptic secondary metabolite gene clusters, it is critical to continue developing methods to activate and enhance secondary metabolite biosynthesis for discovery, development, and large-scale manufacturing. This review covers recent reports on promising new approaches and further validations or technical improvements of existing approaches to strain improvement applicable to a wide range of Streptomyces species and other actinomycetes.

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

Background

Next Generation DNA Sequencing (NGS) and genome mining of actinomycetes and other microorganisms is currently one of the most promising strategies for the discovery of novel bioactive natural products, potentially revealing novel chemistry and enzymology involved in their biosynthesis. This approach also allows rapid insights into the biosynthetic potential of microorganisms isolated from unexploited habitats and ecosystems, which in many cases may prove difficult to culture and manipulate in the laboratory. Streptomyces leeuwenhoekii (formerly Streptomyces sp. strain C34) was isolated from the hyper-arid high-altitude Atacama Desert in Chile and shown to produce novel polyketide antibiotics.

Results

Here we present the de novo sequencing of the S. leeuwenhoekii linear chromosome (8 Mb) and two extrachromosomal replicons, the circular pSLE1 (86 kb) and the linear pSLE2 (132 kb), all in single contigs, obtained by combining Pacific Biosciences SMRT (PacBio) and Illumina MiSeq technologies. We identified the biosynthetic gene clusters for chaxamycin, chaxalactin, hygromycin A and desferrioxamine E, metabolites all previously shown to be produced by this strain (J Nat Prod, 2011, 74:1965) and an additional 31 putative gene clusters for specialised metabolites. As well as gene clusters for polyketides and non-ribosomal peptides, we also identified three gene clusters encoding novel lasso-peptides.

Conclusions

The S. leeuwenhoekii genome contains 35 gene clusters apparently encoding the biosynthesis of specialised metabolites, most of them completely novel and uncharacterised. This project has served to evaluate the current state of NGS for efficient and effective genome mining of high GC actinomycetes. The PacBio technology now permits the assembly of actinomycete replicons into single contigs with >99 % accuracy. The assembled Illumina sequence permitted not only the correction of omissions found in GC homopolymers in the PacBio assembly (exacerbated by the high GC content of actinomycete DNA) but it also allowed us to obtain the sequences of the termini of the chromosome and of a linear plasmid that were not assembled by PacBio. We propose an experimental pipeline that uses the Illumina assembled contigs, in addition to just the reads, to complement the current limitations of the PacBio sequencing technology and assembly software.

Electronic supplementary material

The online version of this article (doi:10.1186/s12864-015-1652-8) contains supplementary material, which is available to authorized users.

Strain-level diversity of secondary metabolism in Streptomyces albus

Streptomyces spp. are robust producers of medicinally-, industrially- and agriculturally-important small molecules. Increased resistance to antibacterial agents and the lack of new antibiotics in the pipeline have led to a renaissance in natural product discovery. This endeavor has benefited from inexpensive high quality DNA sequencing technology, which has generated more than 140 genome sequences for taxonomic type strains and environmental Streptomyces spp. isolates. Many of the sequenced streptomycetes belong to the same species. For instance, Streptomyces albus has been isolated from diverse environmental niches and seven strains have been sequenced, consequently this species has been sequenced more than any other streptomycete, allowing valuable analyses of strain-level diversity in secondary metabolism. Bioinformatics analyses identified a total of 48 unique biosynthetic gene clusters harboured by Streptomyces albus strains. Eighteen of these gene clusters specify the core secondary metabolome of the species. Fourteen of the gene clusters are contained by one or more strain and are considered auxiliary, while 16 of the gene clusters encode the production of putative strain-specific secondary metabolites. Analysis of Streptomyces albus strains suggests that each strain of a Streptomyces species likely harbours at least one strain-specific biosynthetic gene cluster. Importantly, this implies that deep sequencing of a species will not exhaust gene cluster diversity and will continue to yield novelty.