Species-specific secondary metabolite production in marine actinomycetes of the genus Salinispora

A systematic comparison of natural product potential, with an emphasis on RiPPs, by mining of bacteria of three large ecosystems

The implementation of several global microbiome studies has yielded extensive insights into the biosynthetic potential of natural microbial communities. However, studies on the distribution of several classes of ribosomally synthesized and post-translationally modified peptides (RiPPs), non-ribosomal peptides (NRPs) and polyketides (PKs) in different large microbial ecosystems have been very limited. Here, we collected a large set of metagenome-assembled bacterial genomes from marine, freshwater and terrestrial ecosystems to investigate the biosynthetic potential of these bacteria. We demonstrate the utility of public dataset collections for revealing the different secondary metabolite biosynthetic potentials among these different living environments. We show that there is a higher occurrence of RiPPs in terrestrial systems, while in marine systems, we found relatively more terpene-, NRP-, and PK encoding gene clusters. Among the many new biosynthetic gene clusters (BGCs) identified, we analyzed various Nif-11-like and nitrile hydratase leader peptide (NHLP) containing gene clusters that would merit further study, including promising products, such as mersacidin-, LAP- and proteusin analogs. This research highlights the significance of public datasets in elucidating the biosynthetic potential of microbes in different living environments and underscores the wide bioengineering opportunities within the RiPP family.

Comprehensive analysis of genomic variation, pan-genome and biosynthetic potential of Corynebacterium glutamicum strains

Corynebacterium glutamicum is a non-pathogenic species of the Corynebacteriaceae family. It has been broadly used in industrial biotechnology for the production of valuable products. Though it is widely accepted at the industrial level, knowledge about the genomic diversity of the strains is limited. Here, we investigated the comparative genomic features of the strains and pan-genomic characteristics. We also observed phylogenetic relationships among the strains based on average nucleotide identity (ANI). We found diversity between strains at the genomic and pan-genomic levels. Less than one-third of the C. glutamicum pan-genome consists of core genes and soft-core genes. Whereas, a large number of strain-specific genes covered about half of the total pan-genome. Besides, C. glutamicum pan-genome is open and expanding, which indicates the possible addition of new gene families to the pan-genome. We also investigated the distribution of biosynthetic gene clusters (BGCs) among the strains. We discovered slight variations of BGCs at the strain level. Several BGCs with the potential to express novel bioactive secondary metabolites have been identified. Therefore, by utilizing the characteristic advantages of C. glutamicum, different strains can be potential applicants for natural drug discovery.

Isolation of Secondary Metabolites From Marine Actinobacterium of Microbispora sp.T3S11 and Their Antibacterial Activities

Introduction Marine actinobacteria are promising sources of novel bioactive compounds due to their distinct ecological niches and diverse secondary metabolite production capabilities. Among these, Microbispora sp. T3S11 is notable for its unique spore chain structure, which allows for both morphological and genetic identification. Despite its potential, little is understood about the secondary metabolites produced by this strain. In this study, we hope to fill this gap by extracting and analyzing the antibacterial activities of secondary metabolites from Microbispora sp. T3S11, which will be the first time its bioactive compound profile is investigated. Aim To evaluate the antibacterial activity of secondary metabolites isolated from the marine actinobacterium Microbispora sp. T3S11. Materials and methods The antibacterial assays were carried out on agar plates containing the appropriate media for each pathogen. Sterile filter paper disks were impregnated with secondary metabolites extracted from Microbispora sp. T3S11 and placed on the surface of agar plates inoculated with the appropriate pathogens. Similarly, disks containing tetracycline were used as a positive control. The plates were then incubated at the appropriate temperature for each pathogen, and the zones of inhibition around the disks were measured to determine the extracted metabolites' antibacterial activity. Result Secondary metabolites had antimicrobial activity against Streptococcus mutans, Klebsiella pneumonia, and methicillin-resistant Staphylococcus aureus (MRSA). The inhibition of S. mutans was 7.5 mm and 8.5 mm at 75 μg/mL and 100 μg/mL, respectively. Klebsiella pneumonia zones measured 7 mm and 7.5 mm, while MRSA zones measured 7.6 mm and 8.5 mm at the same concentrations. Tetracycline, the standard antibiotic, had larger inhibition zones: 22 mm for S. mutans and Klebsiella pneumonia and 16 mm for MRSA, indicating variable susceptibility. Conclusion We conclude that the secondary metabolites extracted from Microbispora sp. T3S11 exhibits high antibacterial activity. This could be attributed to the presence of various active compounds.

MAR4 Streptomyces: A Unique Resource for Natural Product Discovery

Marine-derived Streptomyces have long been recognized as a source of novel, pharmaceutically relevant natural products. Among these bacteria, the MAR4 clade within the genus Streptomyces has been identified as metabolically rich, yielding over 93 different compounds to date. MAR4 strains are particularly noteworthy for the production of halogenated hybrid isoprenoid natural products, a relatively rare class of bacterial metabolites that possess a wide range of biological activities. MAR4 genomes are enriched in vanadium haloperoxidase and prenyltransferase genes, thus accounting for the production of these compounds. Functional characterization of the enzymes encoded in MAR4 genomes has advanced our understanding of halogenated, hybrid isoprenoid biosynthesis. Despite the exceptional biosynthetic capabilities of MAR4 bacteria, the large body of research they have stimulated has yet to be compiled. Here we review 35 years of natural product research on MAR4 strains and update the molecular diversity of this unique group of bacteria.

OSMAC Method to Assess Impact of Culture Parameters on Metabolomic Diversity and Biological Activity of Marine-Derived Actinobacteria

Actinobacteria are known for their production of bioactive specialized metabolites, but they are still under-exploited. This study uses the "One Strain Many Compounds" (OSMAC) method to explore the potential of three preselected marine-derived actinobacteria: Salinispora arenicola (SH-78) and two Micromonospora sp. strains (SH-82 and SH-57). Various parameters, including the duration of the culture and the nature of the growth medium, were modified to assess their impact on the production of specialized metabolites. This approach involved a characterization based on chemical analysis completed with the construction of molecular networks and biological testing to evaluate cytotoxic and antiplasmodial activities. The results indicated that the influence of culture parameters depended on the studied species and also varied in relation with the microbial metabolites targeted. However, common favorable parameters could be observed for all strains such as an increase in the duration of the culture or the use of the A1 medium. For Micromonospora sp. SH-82, the solid A1 medium culture over 21 days favored a greater chemical diversity. A rise in the antiplasmodial activity was observed with this culture duration, with a IC50 twice as low as for the 14-day culture. Micromonospora sp. SH-57 produced more diverse natural products in liquid culture, with approximately 54% of nodes from the molecular network specifically linked to the type of culture support. Enhanced biological activities were also observed with specific sets of parameters. Finally, for Salinispora arenicola SH-78, liquid culture allowed a greater diversity of metabolites, but intensity variations were specifically observed for some metabolites under other conditions. Notably, compounds related to staurosporine were more abundant in solid culture. Consequently, in the range of the chosen parameters, optimal conditions to enhance metabolic diversity and biological activities in these three marine-derived actinobacteria were identified, paving the way for future isolation works.

Single-cell phenotypes revealed as a key biomarker in bacterial-fungal interactions: a case study of Staphylococcus and Malassezia

IMPORTANCE

Evaluating bacterial-fungal interactions is important for understanding ecological functions in a natural habitat. Many studies have defined bacterial-fungal interactions according to changes in growth rates when co-cultivated. However, the current literature lacks detailed studies on phenotypic changes in single cells associated with transcriptomic profiles to understand the bacterial-fungal interactions. In our study, we measured the single-cell phenotypes of bacteria co-cultivated with fungi using Raman spectroscopy with its transcriptomic profiles and determined the consequence of these interactions in detail. This rapid and reliable phenotyping approach has the potential to provide new insights regarding bacterial-fungal interactions.

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.

Species-specificity of the secondary biosynthetic potential in Bacillus

Introduction

Although Bacillus species have produced a wide variety of structurally diverse and biologically active natural products, the secondary biosynthetic potential of Bacillus species is widely underestimated due to the limited number of biosynthetic gene clusters (BGCs) in this genus. The significant variation in the diversity and novelty of BGCs across different species within the Bacillus genus presents a major obstacle to the efficient discovery of novel natural products from Bacillus.

Methods

In this study, the number of each class of BGCs in all 6,378 high-quality Bacillus genomes was predicted using antiSMASH, the species-specificity of BGC distribution in Bacillus was investigated by Principal component analysis. Then the structural diversity and novelty of the predicted secondary metabolites in Bacillus species with specific BGC distributions were analyzed using molecular networking.

Results

Our results revealed a certain degree of species-specificity in the distribution of BGCs in Bacillus, which was mainly contributed by siderophore, type III polyketide synthase (T3PKS), and transAT-PKS BGCs. B. wiedmannii, B. thuringiensis, and B. cereus are rich in RiPP-like and siderophore BGCs, but lack T3PKS BGCs, while B. amyloliquefaciens and B. velezensis are abundant in transAT-PKS BGCs. These Bacillus species collectively encode 77,541 BGCs, with NRPS and RiPPs being the two most dominant types, which are further categorized into 4,291 GCFs. Remarkably, approximately 54.5% of GCFs and 93.8% of the predicted metabolite scaffolds are found exclusively in a single Bacillus species. Notably, B. cereus, B. thuringiensis, and B. velezensis exhibit the highest potential for producing species-specific NRPS and PKS bioinformatic natural products. Taking two species-specific NRPS gene clusters as examples, the potential of Bacillus to synthesize novel species-specific natural products is illustrated.

Conclusion

This study highlights the species-specificity of the secondary biosynthetic potential in Bacillus and provides valuable insights for the targeted discovery of novel natural products from this genus.

Nanoscaled Discovery of a Shunt Rifamycin from Salinispora arenicola Using a Three-Color GFP-Tagged Staphylococcus aureus Macrophage Infection Assay

Antimicrobial resistance has emerged as a global public health threat, and development of novel therapeutics for treating infections caused by multi-drug resistant bacteria is urgent. Staphylococcus aureus is a major human and animal pathogen, responsible for high levels of morbidity and mortality worldwide. The intracellular survival of S. aureus in macrophages contributes to immune evasion, dissemination, and resilience to antibiotic treatment. Here, we present a confocal fluorescence imaging assay for monitoring macrophage infection by green fluorescent protein (GFP)-tagged S. aureus as a front-line tool to identify antibiotic leads. The assay was employed in combination with nanoscaled chemical analyses to facilitate the discovery of a new, active rifamycin analogue. Our findings indicate a promising new approach for the identification of antimicrobial compounds with macrophage intracellular activity. The antibiotic identified here may represent a useful addition to our armory in tackling the silent pandemic of antimicrobial resistance.

Species-specific secondary metabolism by actinomycetes of the genus Phytohabitans and discovery of new pyranonaphthoquinones and isatin derivatives

To further exploit secondary metabolic potential of a minor actinomycete genus Phytohabitans within the family Micromonosporaceae, metabolite profiling by HPLC-UV analysis, combined with 16S rDNA sequence-based phylotyping were attempted on seven Phytohabitans strains available at the public culture collection. The strains were grouped into three clades and each exhibited unique and distinct metabolite profiles, which were highly conserved among strains within the same clade. These results were consistent with previous observations on two other actinomycetes genera, reconfirming species-specificity of secondary metabolite production, which were conventionally thought to be strain-specific. A strain RD003215, belonging to the P. suffuscus clade, produced multiple metabolites, some of which were presumed to be naphthoquinones. Liquid fermentation followed by chromatographic separation of the broth extract led to the discovery of three new pyranonaphthoquinones, designated habipyranoquinones A-C (1-3), and one new isatin derivative, (R)-N-methyl-3-hydroxy-5,6-dimethoxyoxindole (4), along with three known synthetic compounds, 6,8-dihydroxydehydro-α-lapachone (5), N-methyl-5,6-dimethoxyisatin (6), and 5,6-dimethoxyisatin (7). Structures of 1-4 were unequivocally elucidated by NMR, MS, and CD spectral analysis, with assistance of density functional theory-based NMR chemical shift prediction and ECD spectral calculation. Compound 2 displayed antibacterial activity against Kocuria rhizophila and Staphylococcus aureus with MIC 50 µg/mL and cytotoxicity against P388 murine leukemia cells with an IC₅₀ value of 34 µM. Compounds 1 and 4 also showed cytotoxicity against P388 cells with IC₅₀ values of 29 and 14 µM, respectively.

Marine-derived antimicrobial molecules from the sponges and their associated bacteria

Antimicrobial resistance (AMR) is one of the leading global health issues that demand urgent attention. Very soon the world will have to bear the consequences of increased drug resistance if new anti-infectives are not pumped into the clinical pipeline in a short period. This presses on the need for novel chemical entities, and the marine environment is one such hotspot to look for. The Ocean harbours a variety of organisms, of which from this aspect, "Sponges (Phylum Porifera)" are of particular interest. To tackle the stresses faced due to their sessile and filter-feeding lifestyle, sponges produce various bioactive compounds, which can be tapped for human use. The sponges harbour several microorganisms of different types and in most cases; the microbial symbionts are the actual producers of the bioactive compounds. This review describes the alarming need for the development of new antimicrobials and how marine sponges can contribute to this. Selected antimicrobial compounds from the marine sponges and their associated bacteria have been described. Additionally, measures to tackle the supply problem have been covered, which is the primary obstacle in marine natural product drug discovery.

Streptomyces sp. BV410: Interspecies cross-talk for staurosporine production

AIMS

Sequencing and genome analysis of two co-isolated streptomycetes, named BV410-1 and BV410-10, and the effect of their co-cultivation on the staurosporine production.

METHODS AND RESULTS

Identification of two strains through genome sequencing and their separation using different growth media was conducted. Sequence analysis revealed that the genome of BV410-1 was 9.5 Mb, whilst that of BV410-10 was 7.1 Mb. AntiSMASH analysis identified 28 biosynthetic gene clusters (BGCs) from BV410-1, including that responsible for staurosporine biosynthesis, whilst 20 BGCs were identified from BV410-10. The addition of cell-free supernatant from BV410-10 monoculture to BV410-1 fermentations improved the staurosporine yield from 8.35 mg L^-1 up to 15.85 mg L^-1 , whilst BV410-10 monoculture ethyl acetate extract did not have the same effect. Also, there was no improvement in staurosporine production when artificial mixed cultures were created using three different BV410-1 and BV410-10 spore ratios.

CONCLUSIONS

The growth of BV410-10 was inhibited when the two strains were grown together on agar plates. Culture supernatants of BV410-10 showed potential to stimulate staurosporine production in BV410-1, but overall co-cultivation attempts did not restore the previously reported yield of staurosporine produced by the original mixed isolate.

SIGNIFICANCE AND IMPACT OF STUDY

This work confirmed complex relations between streptomycetes in soil that are difficult to recreate under the laboratory conditions. Also, mining of streptomycetes genomes that mainly produce known bioactive compounds could still be the fruitful approach in search for novel bioactive molecules.

Natural Products from Actinobacteria as a Potential Source of New Therapies Against Colorectal Cancer: A Review

Colorectal cancer (CRC) is a common, and deadly disease. Despite the improved knowledge on CRC heterogeneity and advances in the medical sciences, there is still an urgent need to cope with the challenges and side effects of common treatments for the disease. Natural products (NPs) have always been of interest for the development of new medicines. Actinobacteria are known to be prolific producers of a wide range of bioactive NPs, and scientific evidence highlights their important protective role against CRC. This review is a holistic picture on actinobacter-derived cytotoxic compounds against CRC that provides a good perspective for drug development and design in near future. This review also describes the chemical structure of 232 NPs presenting anti-CRC activity with the being majority of quinones, lactones, alkaloids, peptides, and glycosides. The study reveals that most of these NPs are derived from marine actinobacteria followed by terrestrial and endophytic actinobacteria, respectively. They are predominantly produced by Streptomyces, Micromonospors, Saliniospors and Actinomadura, respectively, in which Streptomyces, as the predominant contributor generating over 76% of compounds exclusively. Besides it provides a valuable snapshot of the chemical structure-activity relationship of compounds, highlighting the presence or absence of some specific atoms and chemical units in the structure of compounds can greatly influence their biological activities. To the best of our knowledge, this is the first comprehensive review on natural actinobacterial compounds affecting different types of CRC. Our study reveals that the high diversity of actinobacterial strains and their NPs derivatives, described here provides a new perspective and direction for the production of new anti-CRC drugs and paves the way to innovation for drugs discovery in the future. The knowledge obtain from this review can help us to understand the pivotal application of actinobacteria in future drugs development.

Targeting Streptomyces-Derived Streptenol Derivatives against Gynecological Cancer Target PIK3CA: An In Silico Approach

Streptomyces is amongst the most amenable genera for biotechnological applications, and it is extensively used as a scaffold for drug development. One of the most effective therapeutic applications in the treatment of cancer is targeted therapy. Small molecule therapy is one of them, and it has gotten a lot of attention recently. Streptomyces derived compounds namely streptenols A, C, and F-I and streptazolin were subjected for ADMET property assessment. Our computational studies based on molecular docking effectively displayed the synergistic effect of streptomyces-derived compounds on the gynecological cancer target PIK3CA. These compounds were observed with the highest docking scores as well as promising intermolecular interaction stability throughout the molecular dynamic simulation. Molecular docking and molecular dynamic modeling techniques were utilized to investigate the binding mode stability of drugs using a pharmacophore scaffold, as well as physicochemical and pharmacokinetic aspects linked to alpelisib. With a root mean square fluctuation of the protein backbone of less than 0.7 nm, they demonstrated a steady binding mode in the target binding pocket. They have also prompted hydrogen bonding throughout the simulations, implying that the chemicals have firmly occupied the active site. A comprehensive study showed that streptenol D, streptenol E, streptenol C, streptenol G, streptenol F, and streptenol B can be considered as lead compounds for PIK3CA-based inhibitor design. To warrant the treatment efficacy against cancer, comprehensive computational research based on proposed chemicals must be assessed through in vitro studies.

Tromethamine and dodecanol appear to be the major secondary metabolites of Streptomyces decoyicus M

An isolate of Streptomyces decoyicus M* (code of the isolate) was identified by the sequencing of 16S rRNA gene. It was grown on solid media and secondary metabolites were extracted with n-butanol. The extract was dried and run in a sodium dodecyl sulphate-polyacrylamide gel (SDS-PAGE, 10%). Two main bands obtained were sliced and the metabolites were regained in n-butanol. These two samples were then identified by gas-chromatography-mass spectrometry (GC-MS), and Fourier-transform infrared spectroscopy (FT-IR). The results demonstrated that tromethamine- and 1-dodecanol were the main constituents (band 1: 61% and 17.7%; band 2: 41% and 54%, respectively). This finding maintained that the isolate of Streptomyces decoyicus produced high amounts tromethamine- and 1-dodecanol under the conditions investigated.

Metabolome analysis of genus Forsythia related constituents in Forsythia suspensa leaves and fruits using UPLC-ESI-QQQ-MS/MS technique

Forsythia suspensa is a traditional Chinese herb. Its numerous metabolites have important roles, as they possessed a wide range of biological activities. This study explored the accumulations of F. suspensa metabolites by performing widely targeted metabolomic analysis. The metabolites were studied at four stages of fruit development. Metabolites in the fruits and leaves of F. suspensa during fruit development included phenolic acids, flavonoids, lipids, lignans and coumarins, amino acids and their derivatives, terpenes, organic acids, nucleotides and their derivatives, alkaloids, quinones, steroids, and tannins. Fourteen Forsythia related metabolites were detected. Their contents varied among the developmental stages. Statistically significant correlations were found between the levels of forsythoside B and 11-methyl-forsythide, and forsythialan B and phillygenin, in both leaves and fruits. According to the correlation analysis between metabolites, Forsythia related metabolites were divided into two classes and five subclasses. In total, 33 compounds presented significant correlations in both fruits and leaves, which indicated the potential relationship in the synthesis of Forsythia related metabolites. Forsythialan B and phillygenin were both negatively correlated with L-valine, while Z-6,7-epoxyligustilid was positively correlated with both compounds. The quality control compounds forsythiaside A and phillyrin were positively and negatively correlated with uracil, respectively. These metabolomics results may facilitate the biosynthesis of Forsythia related metabolites.

An Unprecedented Number of Cytochrome P450s Are Involved in Secondary Metabolism in Salinispora Species

Cytochrome P450 monooxygenases (CYPs/P450s) are heme thiolate proteins present in species across the biological kingdoms. By virtue of their broad substrate promiscuity and regio- and stereo-selectivity, these enzymes enhance or attribute diversity to secondary metabolites. Actinomycetes species are well-known producers of secondary metabolites, especially Salinispora species. Despite the importance of P450s, a comprehensive comparative analysis of P450s and their role in secondary metabolism in Salinispora species is not reported. We therefore analyzed P450s in 126 strains from three different species Salinispora arenicola, S. pacifica, and S. tropica. The study revealed the presence of 2643 P450s that can be grouped into 45 families and 103 subfamilies. CYP107 and CYP125 families are conserved, and CYP105 and CYP107 families are bloomed (a P450 family with many members) across Salinispora species. Analysis of P450s that are part of secondary metabolite biosynthetic gene clusters (smBGCs) revealed Salinispora species have an unprecedented number of P450s (1236 P450s-47%) part of smBGCs compared to other bacterial species belonging to the genera Streptomyces (23%) and Mycobacterium (11%), phyla Cyanobacteria (8%) and Firmicutes (18%) and the classes Alphaproteobacteria (2%) and Gammaproteobacteria (18%). A peculiar characteristic of up to six P450s in smBGCs was observed in Salinispora species. Future characterization Salinispora species P450s and their smBGCs have the potential for discovering novel secondary metabolites.

Relationship between bacterial phylotype and specialized metabolite production in the culturable microbiome of two freshwater sponges

Microbial drug discovery programs rely heavily on accessing bacterial diversity from the environment to acquire new specialized metabolite (SM) lead compounds for the therapeutic pipeline. Therefore, knowledge of how commonly culturable bacterial taxa are distributed in nature, in addition to the degree of variation of SM production within those taxa, is critical to informing these front-end discovery efforts and making the overall sample collection and bacterial library creation process more efficient. In the current study, we employed MALDI-TOF mass spectrometry and the bioinformatics pipeline IDBac to analyze diversity within phylotype groupings and SM profiles of hundreds of bacterial isolates from two Eunapius fragilis freshwater sponges, collected 1.5 km apart. We demonstrated that within two sponge samples of the same species, the culturable bacterial populations contained significant overlap in approximate genus-level phylotypes but mostly nonoverlapping populations of isolates when grouped lower than the level of genus. Further, correlations between bacterial phylotype and SM production varied at the species level and below, suggesting SM distribution within bacterial taxa must be analyzed on a case-by-case basis. Our results suggest that two E. fragilis freshwater sponges collected in similar environments can exhibit large culturable diversity on a species-level scale, thus researchers should scrutinize the isolates with analyses that take both phylogeny and SM production into account to optimize the chemical space entering into a downstream bacterial library.

Rare actinobacteria isolated from the hypersaline Ojo de Liebre Lagoon as a source of novel bioactive compounds with biotechnological potential

The Ojo de Liebre Lagoon is a Marine Protected Area that lies within a UNESCO World Heritage Site and is a critical habitat for important migratory species such as the grey whale and bird species. Unique hypersaline environments, such as the Ojo de Liebre Lagoon, are underexplored in terms of their bacterial and chemical diversity, representing a potential source for new bioactive compounds with pharmacological properties. Actinobacteria are one of the most diverse and prolific taxonomic bacterial groups in terms of marine bioactive compounds. This study aimed to identify the culturable actinobacterial community inhabiting the Lagoon, as well as to test their potential as new sources of anticancer compounds with pharmacological potential. A selective isolation approach focused on spore-forming bacteria from 40 sediment samples generated a culture collection of 64 strains. The 16S rRNA gene analyses identified three phyla in this study, the Actinobacteria, Firmicutes and Proteobacteria, where the phylum Actinobacteria dominated (57%) the microbial community profiles. Within the Actinobacteria, nine different genera were isolated including the Actinomadura, Micromonospora, Nocardiopsis, Plantactinospora and Streptomyces sp. We observed seasonal differences on actinobacteria recovery. For instance, Micromonospora strains were recovered during the four sampling seasons, while Arthrobacter and Pseudokineococcus were only isolated in February 2018, and Blastococcus, Rhodococcus and Streptomyces were uniquely isolated in June 2018. Ethyl acetate crude extracts derived from actinobacterial cultures were generated and screened for cytotoxic activity against six cancer cell lines. Strains showed promising low percentages of viability on lung (H1299), cervical (SiHa), colon (Caco-2) and liver (HepG2) cancer lines. Molecular networking results suggest many of the metabolites produced by these strains are unknown and they might harbour novel chemistry. Our results showed the Ojo de Liebre Lagoon is a novel source for isolating diverse marine actinobacteria which produce promising bioactive compounds for potential biotechnological use as anticancer agents.

Promising bioactive compounds from the marine environment and their potential effects on various diseases

Background

The marine environment hosts a wide variety of species that have evolved to live in harsh and challenging conditions. Marine organisms are the focus of interest due to their capacity to produce biotechnologically useful compounds. They are promising biocatalysts for new and sustainable industrial processes because of their resistance to temperature, pH, salt, and contaminants, representing an opportunity for several biotechnological applications. Encouraged by the extensive and richness of the marine environment, marine organisms’ role in developing new therapeutic benefits is heading as an arable field.

Main body of the abstract

There is currently much interest in biologically active compounds derived from natural resources, especially compounds that can efficiently act on molecular targets, which are involved in various diseases. Studies are focused on bacteria and fungi, isolated from sediments, seawater, fish, algae, and most marine invertebrates such as sponges, mollusks, tunicates, coelenterates, and crustaceans. In addition to marine macro-organisms, such as sponges, algae, or corals, marine bacteria and fungi have been shown to produce novel secondary metabolites (SMs) with specific and intricate chemical structures that may hold the key to the production of novel drugs or leads. The marine environment is known as a rich source of chemical structures with numerous beneficial health effects. Presently, several lines of studies have provided insight into biological activities and neuroprotective effects of marine algae, including antioxidant, anti-neuroinflammatory, cholinesterase inhibitory activity, and neuronal death inhibition.

Conclusion

The application of marine-derived bioactive compounds has gained importance because of their therapeutic uses in several diseases. Marine natural products (MNPs) display various pharmaceutically significant bioactivities, including antibiotic, antiviral, neurodegenerative, anticancer, or anti-inflammatory properties. The present review focuses on the importance of critical marine bioactive compounds and their role in different diseases and highlights their possible contribution to humanity.

Biological Control of Fusarium oxysporum f. sp. cubense Tropical Race 4 in Banana Plantlets Using Newly Isolated Streptomyces sp. WHL7 from Marine Soft Coral

Banana Fusarium wilt caused by Fusarium oxysporum f. sp. cubense is a disastrous fungal disease. Foc tropical race 4 (Foc TR4) infects almost all banana cultivars. Use of chemical fungicides caused serious environment pollution. Biological control with antagonistic microbes is a promising strategy for controlling Foc TR4. Here, strain WHL7 isolated from marine soft coral exhibited a high antifungal activity against Foc TR4. Based on the morphological and physicochemical profiles as well as the phylogenetic tree, the strain was assigned to Streptomyces sp. Fermentation broth of Streptomyces sp. WHL7 significantly increased the resistance of banana plantlets to Foc TR4 in the pot experiment. Analysis of antifungal mechanism showed that strain WHL7 extracts inhibited spore germination and mycelial growth of Foc TR4, and destroyed cell integrity and ultrastructure. Hence, Streptomyces sp. WHL7 is an important bioresource for exploring novel natural products and biofertilizer to manage Foc TR4.

The Diversity, Metabolomics Profiling, and the Pharmacological Potential of Actinomycetes Isolated from the Estremadura Spur Pockmarks (Portugal)

The Estremadura Spur pockmarks are a unique and unexplored ecosystem located in the North Atlantic, off the coast of Portugal. A total of 85 marine-derived actinomycetes were isolated and cultured from sediments collected from this ecosystem at a depth of 200 to 350 m. Nine genera, Streptomyces, Micromonospora, Saccharopolyspora, Actinomadura, Actinopolymorpha, Nocardiopsis, Saccharomonospora, Stackebrandtia, and Verrucosispora were identified by 16S rRNA gene sequencing analyses, from which the first two were the most predominant. Non-targeted LC-MS/MS, in combination with molecular networking, revealed high metabolite diversity, including several known metabolites, such as surugamide, antimycin, etamycin, physostigmine, desferrioxamine, ikarugamycin, piericidine, and rakicidin derivatives, as well as numerous unidentified metabolites. Taxonomy was the strongest parameter influencing the metabolite production, highlighting the different biosynthetic potentials of phylogenetically related actinomycetes; the majority of the chemical classes can be used as chemotaxonomic markers, as the metabolite distribution was mostly genera-specific. The EtOAc extracts of the actinomycete isolates demonstrated antimicrobial and antioxidant activity. Altogether, this study demonstrates that the Estremadura Spur is a source of actinomycetes with potential applications for biotechnology. It highlights the importance of investigating actinomycetes from unique ecosystems, such as pockmarks, as the metabolite production reflects their adaptation to this habitat.

Vertical Inheritance Facilitates Interspecies Diversification in Biosynthetic Gene Clusters and Specialized Metabolites

While specialized metabolites are thought to mediate ecological interactions, the evolutionary processes driving chemical diversification, particularly among closely related lineages, remain poorly understood. Here, we examine the evolutionary dynamics governing the distribution of natural product biosynthetic gene clusters (BGCs) among 118 strains representing all nine currently named species of the marine actinobacterial genus Salinispora. While much attention has been given to the role of horizontal gene transfer (HGT) in structuring BGC distributions, we find that vertical descent facilitates interspecies BGC diversification over evolutionary timescales. Moreover, we identified a distinct phylogenetic signal among Salinispora species at both the BGC and metabolite level, indicating that specialized metabolism represents a conserved phylogenetic trait. Using a combination of genomic analyses and liquid chromatography–high-resolution tandem mass spectrometry (LC-MS/MS) targeting nine experimentally characterized BGCs and their small molecule products, we identified gene gain/loss events, constrained interspecies recombination, and other evolutionary processes associated with vertical inheritance as major contributors to BGC diversification. These evolutionary dynamics had direct consequences for the compounds produced, as exemplified by species-level differences in salinosporamide production. Together, our results support the concept that specialized metabolites, and their cognate BGCs, can represent phylogenetically conserved functional traits with chemical diversification proceeding in species-specific patterns over evolutionary time frames.

Rausuquinone, a non-glycosylated pluramycin-class antibiotic from Rhodococcus

A new pluramycin-class polyketide, rausuquinone (1), and its known congener hydramycin (2) were isolated from the culture extract of the deep-sea water-derived Rhodococcus sp. RD015140. Compound 1 possesses a γ-pyrone-fused anthraquinone core with a 3-butene-1,2-diol side chain. Structures of 1 was determined by extensive analysis of 1D and 2D NMR spectroscopic data. Compound 1 showed antimicrobial activity against Gram-positive bacteria. This is the first discovery of aromatic polyketides from the genus Rhodococcus.

Specialized Metabolite Mediated Predation Defense in the Marine Actinobacterium Salinispora

The obligate marine actinobacterial genus Salinispora has become a model organism for natural product discovery, yet little is known about the ecological functions of the compounds produced by this taxon. The aims of this study were to assess the effects of live cultures and culture extracts from two Salinispora species on invertebrate predators. In choice-based feeding experiments using the bacterivorous nematode Caenorhabditis elegans, live cultures of both Salinispora species were less preferred than E. coli. When given a choice between the two species, C. elegans preferred S. areniolca over S. tropica. Culture extracts from S. tropica deterred C. elegans while those from S. arenicola did not, suggesting that compounds produced by S. tropica may account for the feeding deterrence. Bioactivity guided isolation linked compounds in the lomaiviticin series to the deterrent activity. Additional assays using the marine polychaete Ophryotrocha siberti and marine nematodes further support the deterrent activity of S. tropica against potential predators. These results provide evidence that Salinispora natural products may function as a defense against predation and that the strategies of predation defense differ between closely related species. Importance Bacteria inhabiting marine sediments are subject to predation by bacterivorous eukaryotes. Here we test the hypothesis that sediment-derived bacteria in the genus Salinispora produce biologically active natural products that function as a defense against predation. The results reveal that cultures and culture extracts of S. tropica deter feeding by Caenorhabditis elegans and negatively affect the habitat preference of a marine annelid (Ophryotrocha siberti). These activities were linked to the lomaiviticins, a series of cytotoxic compounds produced by S. tropica. Microbial natural products that function as a defense against predation represent a poorly understood trait that can influence community structure in marine sediments.

Marine-derived pipeline anticancer natural products: a review of their pharmacotherapeutic potential and molecular mechanisms

Background

Cancer is a complex and most widespread disease and its prevalence is increasing worldwide, more in countries that are witnessing urbanization and rapid industrialization changes. Although tremendous progress has been made, the interest in targeting cancer has grown rapidly every year. This review underscores the importance of preventive and therapeutic strategies.

Main text

Natural products (NPs) from various sources including plants have always played a crucial role in cancer treatment. In this growing list, numerous unique secondary metabolites from marine sources have added and gaining attention and became potential players in drug discovery and development for various biomedical applications. Many NPs found in nature that normally contain both pharmacological and biological activity employed in pharmaceutical industry predominantly in anticancer pharmaceuticals because of their enormous range of structure entities with unique functional groups that attract and inspire for the creation of several new drug leads through synthetic chemistry. Although terrestrial medicinal plants have been the focus for the development of NPs, however, in the last three decades, marine origins that include invertebrates, plants, algae, and bacteria have unearthed numerous novel pharmaceutical compounds, generally referred as marine NPs and are evolving continuously as discipline in the molecular targeted drug discovery with the inclusion of advanced screening tools which revolutionized and became the component of antitumor modern research.

Conclusions

This comprehensive review summarizes some important and interesting pipeline marine NPs such as Salinosporamide A, Dolastatin derivatives, Aplidine/plitidepsin (Aplidin®) and Coibamide A, their anticancer properties and describes their mechanisms of action (MoA) with their efficacy and clinical potential as they have attracted interest for potential use in the treatment of various types of cancers.

Biologically Active Antimicrobial Compounds from Marine Microorganisms (2005-2019)

INTRODUCTION

The increase in contagious diseases like nosocomial infections, urinary tract infections, and meningitis has led to the emergence of antimicrobial resistance urgently needs new antimicrobial medication with new modes of action. Some of the antibiotics present in the market have been obtained from terrestrial plants, or extracted semisynthetically from materials which can be fermented.

METHODS

Marine microorganisms account for approximately 80% of sea biomass. They are essential for the survival and well-being of aquatic habitats due to their indispensable contribution to biogeochemical cycles and biological processes. In marine ecosystems, microorganisms live as microbial communities in seawater, where symbiotic relationships are formed, and their ecological functions are fulfilled.

RESULTS

Marine microorganisms remain the largest, most diverse and most exciting source of structurally and functionally complex antimicrobial agents. They are extremely involved in their structure and functions. Enormous biological wealth lies in marine habitats. These microorganisms are potential sources of novel antimicrobial compounds to combat the most infectious diseases like nosocomial infections, and urinary tract infections.

CONCLUSION

This study deals with biologically active antimicrobial compounds taken from marine microorganism source, which was reported between the years 2005 and 2019. This review highlights their chemical groups, their bioactivities and sources. Marine microorganism exploitation techniques have also been reported by the authors.

Marine Actinomycetes, New Sources of Biotechnological Products

The Actinomycetales order is one of great genetic and functional diversity, including diversity in the production of secondary metabolites which have uses in medical, environmental rehabilitation, and industrial applications. Secondary metabolites produced by actinomycete species are an abundant source of antibiotics, antitumor agents, anthelmintics, and antifungals. These actinomycete-derived medicines are in circulation as current treatments, but actinomycetes are also being explored as potential sources of new compounds to combat multidrug resistance in pathogenic bacteria. Actinomycetes as a potential to solve environmental concerns is another area of recent investigation, particularly their utility in the bioremediation of pesticides, toxic metals, radioactive wastes, and biofouling. Other applications include biofuels, detergents, and food preservatives/additives. Exploring other unique properties of actinomycetes will allow for a deeper understanding of this interesting taxonomic group. Combined with genetic engineering, microbial experimental evolution, and other enhancement techniques, it is reasonable to assume that the use of marine actinomycetes will continue to increase. Novel products will begin to be developed for diverse applied research purposes, including zymology and enology. This paper outlines the current knowledge of actinomycete usage in applied research, focusing on marine isolates and providing direction for future research.

Marine Sediment Recovered Salinispora sp. Inhibits the Growth of Emerging Bacterial Pathogens and other Multi-Drug-Resistant Bacteria

Marine obligate actinobacteria produce a wide variety of secondary metabolites with biological activity, notably those with antibiotic activity urgently needed against multi-drug-resistant bacteria. Seventy-five marine actinobacteria were isolated from a marine sediment sample collected in Punta Arena de La Ventana, Baja California Sur, Mexico. The 16S rRNA gene identification, Multi Locus Sequence Analysis, and the marine salt requirement for growth assigned seventy-one isolates as members of the genus Salinispora, grouped apart but related to the main Salinispora arenicola species clade. The ability of salinisporae to inhibit bacterial growth of Staphylococcus epidermidis, Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacer baumannii, Pseudomonas aeruginosa, and Enterobacter spp. was evaluated by cross-streaking plate and supernatant inhibition tests. Ten supernatants inhibited the growth of eight strains of S. epidermidis from patients suffering from ocular infections, two out of the eight showed growth inhibition on ten S. epidermidis strains from prosthetic joint infections. Also, it inhibited the growth of the remaining six multi-drug-resistant bacteria tested. These results showed that some Salinispora strains could produce antibacterial compounds to combat bacteria of clinical importance and prove that studying different geographical sites uncovers untapped microorganisms with metabolic potential.

Expansion of Gamma-Butyrolactone Signaling Molecule Biosynthesis to Phosphotriester Natural Products

Bacterial hormones, such as the iconic gamma-butyrolactone A-factor, are essential signaling molecules that regulate diverse physiological processes, including specialized metabolism. These low molecular weight compounds are common in Streptomyces species and display species-specific structural differences. Recently, unusual gamma-butyrolactone natural products called salinipostins were isolated from the marine actinomycete genus Salinispora based on their antimalarial properties. As the salinipostins possess a rare phosphotriester motif of unknown biosynthetic origin, we set out to explore its construction by the widely conserved 9-gene spt operon in Salinispora species. We show through a series of in vivo and in vitro studies that the spt gene cluster dually encodes the salinipostins and newly identified natural A-factor-like gamma-butyrolactones (Sal-GBLs). Remarkably, homologous biosynthetic gene clusters are widely distributed among many actinomycete genera, including Streptomyces, suggesting the significance of this operon in bacteria.

Draft Genome Sequence of Salinispora sp. Strain H7-4, Isolated from Deep-Sea Sediments of the Shikoku Basin

Salinispora spp. are obligate marine actinomycetes reported mainly from shallow tropical and subtropical marine habitats. In this announcement, we present the isolation and the draft genome sequence of Salinispora sp. strain H7-4 of a new 16S rDNA phylotype from deep-sea sediments of the Shikoku Basin.

Salinispora spp. are obligate marine actinomycetes reported mainly from shallow tropical and subtropical marine habitats. In this announcement, we present the isolation and draft genome sequence of Salinispora sp. strain H7-4 of a new 16S rDNA phylotype from deep-sea sediments of the Shikoku Basin.

Antimicrobial Chlorinated 3-Phenylpropanoic Acid Derivatives from the Red Sea Marine Actinomycete Streptomyces coelicolor LY001

The actinomycete strain Streptomyces coelicolor LY001 was purified from the sponge Callyspongia siphonella. Fractionation of the antimicrobial extract of the culture of the actinomycete afforded three new natural chlorinated derivatives of 3-phenylpropanoic acid, 3-(3,5-dichloro-4-hydroxyphenyl)propanoic acid (1), 3-(3,5-dichloro-4-hydroxyphenyl)propanoic acid methyl ester (2), and 3-(3-chloro-4-hydroxyphenyl)propanoic acid (3), together with 3-phenylpropanoic acid (4), E-cinnamic acid (5), and the diketopiperazine alkaloids cyclo(l-Phe-trans-4-OH-l-Pro) (6) and cyclo(l-Phe-cis-4-OH-d-Pro) (7) were isolated. Interpretation of nuclear magnetic resonance (NMR) and high-resolution electrospray ionization mass spectrometry (HRESIMS) data of 1–7 supported their assignments. Compounds 1–3 are first candidates of the natural chlorinated phenylpropanoic acid derivatives. The production of the chlorinated derivatives of 3-phenylpropionic acid (1–3) by S. coelicolor provides insight into the biosynthetic capabilities of the marine-derived actinomycetes. Compounds 1–3 demonstrated significant and selective activities towards Escherichia. coli and Staphylococcus aureus, while Candida albicans displayed more sensitivity towards compounds 6 and 7, suggesting a selectivity effect of these compounds against C. albicans.

Expanding the Diversity of Bacterioplankton Isolates and Modeling Isolation Efficacy with Large-Scale Dilution-to-Extinction Cultivation

Even before the coining of the term “great plate count anomaly” in the 1980s, scientists had noted the discrepancy between the number of microorganisms observed under the microscope and the number of colonies that grew on traditional agar media. New cultivation approaches have reduced this disparity, resulting in the isolation of some of the “most wanted” bacterial lineages. Nevertheless, the vast majority of microorganisms remain uncultured, hampering progress toward answering fundamental biological questions about many important microorganisms. Furthermore, few studies have evaluated the underlying factors influencing cultivation success, limiting our ability to improve cultivation efficacy. Our work details the use of dilution-to-extinction (DTE) cultivation to expand the phylogenetic and geographic diversity of available axenic cultures. We also provide a new model of the DTE approach that uses cultivation results and natural abundance information to predict taxon-specific viability and iteratively constrain DTE experimental design to improve cultivation success.

Cultivated bacterioplankton representatives from diverse lineages and locations are essential for microbiology, but the large majority of taxa either remain uncultivated or lack isolates from diverse geographic locales. We paired large-scale dilution-to-extinction (DTE) cultivation with microbial community analysis and modeling to expand the phylogenetic and geographic diversity of cultivated bacterioplankton and to evaluate DTE cultivation success. Here, we report results from 17 DTE experiments totaling 7,820 individual incubations over 3 years, yielding 328 repeatably transferable isolates. Comparison of isolates to microbial community data for source waters indicated that we successfully isolated 5% of the observed bacterioplankton community throughout the study; 43% and 26% of our isolates matched operational taxonomic units and amplicon single-nucleotide variants, respectively, within the top 50 most abundant taxa. Isolates included those from previously uncultivated clades such as SAR11 LD12 and Actinobacteria acIV, as well as geographically novel members from other ecologically important groups like SAR11 subclade IIIa, SAR116, and others, providing isolates in eight putatively new genera and seven putatively new species. Using a newly developed DTE cultivation model, we evaluated taxon viability by comparing relative abundance with cultivation success. The model (i) revealed the minimum attempts required for successful isolation of taxa amenable to growth on our media and (ii) identified possible subpopulation viability variation in abundant taxa such as SAR11 that likely impacts cultivation success. By incorporating viability in experimental design, we can now statistically constrain the effort necessary for successful cultivation of specific taxa on a defined medium.

IMPORTANCE Even before the coining of the term “great plate count anomaly” in the 1980s, scientists had noted the discrepancy between the number of microorganisms observed under the microscope and the number of colonies that grew on traditional agar media. New cultivation approaches have reduced this disparity, resulting in the isolation of some of the “most wanted” bacterial lineages. Nevertheless, the vast majority of microorganisms remain uncultured, hampering progress toward answering fundamental biological questions about many important microorganisms. Furthermore, few studies have evaluated the underlying factors influencing cultivation success, limiting our ability to improve cultivation efficacy. Our work details the use of dilution-to-extinction (DTE) cultivation to expand the phylogenetic and geographic diversity of available axenic cultures. We also provide a new model of the DTE approach that uses cultivation results and natural abundance information to predict taxon-specific viability and iteratively constrain DTE experimental design to improve cultivation success.

Six novel species of the obligate marine actinobacterium Salinispora, Salinispora cortesiana sp. nov., Salinispora fenicalii sp. nov., Salinispora goodfellowii sp. nov., Salinispora mooreana sp. nov., Salinispora oceanensis sp. nov. and Salinispora vitiensis sp. nov., and emended description of the genus Salinispora

Ten representative actinobacterial strains isolated from marine sediments collected worldwide were studied to determine their taxonomic status. The strains were previously identified as members of the genus Salinispora and shared >99 % 16S rRNA gene sequence similarity to the three currently recognized Salinispora species. Comparative genomic analyses resulted in the delineation of six new species based on average nucleotide identity and digital DNA-DNA hybridization values below 95 and 70 %, respectively. The species status of the six new groups was supported by a core-genome phylogeny reconstructed from 2106 orthologs detected in 118 publicly available Salinispora genomes. Chemotaxonomic and physiological studies were used to complete the phenotypic characterization of the strains. The fatty acid profiles contained the major components iso-C_16 : 0, C_15 : 0, iso-_17 : 0 and anteiso C_17 : 0. Galactose and xylose were common in all whole-sugar patterns but differences were found between the six groups of strains. Polar lipid compositions were also unique for each species. Distinguishable physiological and biochemical characteristics were also recorded. The names proposed are Salinispora cortesiana sp. nov., CNY-202^T (=DSM 108615^T=CECT 9739^T); Salinispora fenicalii sp. nov., CNT-569^T (=DSM 108614^T=CECT 9740^T); Salinispora goodfellowii sp. nov., CNY-666^T (=DSM 108616^T=CECT 9738^T); Salinispora mooreana sp. nov., CNT-150^T (=DSM 45549^T=CECT 9741^T); Salinispora oceanensis sp. nov., CNT-138^T (=DSM 45547^T=CECT 9742^T); and Salinispora vitiensis sp. nov., CNT-148^T (=DSM 45548^T=CECT 9743^T).

Extending the Salinilactone Family

Five new members of the salinilactone family, salinilactones D-H, are reported. These bicyclic lactones are produced by Salinispora bacteria and display extended or shortened alkyl side chains relative to the recently reported salinilactones A-C. They were identified by GC/MS, gas chromatographic retention index, and comparison with synthetic samples. We further investigated the occurrence of salinilactones across six newly proposed Salinispora species to gain insight into how compound production varies among taxa. The growth-inhibiting effect of this compound family on multiple biological systems including non-Salinispora actinomycetes was analyzed. Additionally, we found strong evidence for significant cytotoxicity of the title compounds.

Microbial Natural Products in Drug Discovery

Over a long period of time, humans have explored many natural resources looking for remedies of various ailments. Traditional medicines have played an intrinsic role in human life for thousands of years, with people depending on medicinal plants and their products as dietary supplements as well as using them therapeutically for treatment of chronic disorders, such as cancer, malaria, diabetes, arthritis, inflammation, and liver and cardiac disorders. However, plant resources are not sufficient for treatment of recently emerging diseases. In addition, the seasonal availability and other political factors put constrains on some rare plant species. The actual breakthrough in drug discovery came concurrently with the discovery of penicillin from Penicillium notatum in 1929. This discovery dramatically changed the research of natural products and positioned microbial natural products as one of the most important clues in drug discovery due to availability, variability, great biodiversity, unique structures, and the bioactivities produced. The number of commercially available therapeutically active compounds from microbial sources to date exceeds those discovered from other sources. In this review, we introduce a short history of microbial drug discovery as well as certain features and recent research approaches, specifying the microbial origin, their featured molecules, and the diversity of the producing species. Moreover, we discuss some bioactivities as well as new approaches and trends in research in this field.

Bioassay- and metabolomics-guided screening of bioactive soil actinomycetes from the ancient city of Ihnasia, Egypt

Literature surveys, taxonomical differences, and bioassay results have been utilized in the discovery of new natural products to aid in Actinomycetes isolate-selection. However, no or less investigation have been done on establishing the differences in metabolomic profiles of the isolated microorganisms. The study aims to utilise bioassay- and metabolomics-guided tools that included dereplication study and multivariate analysis of the NMR and mass spectral data of microbial extracts to assist the selection of isolates for scaling-up the production of antimicrobial natural products. A total of 58 actinomycetes were isolated from different soil samples collected from Ihnasia City, Egypt and screened for their antimicrobial activities against indicator strains that included Bacillus subtilis, Escherichia coli, methicillin-resistant Staphylococcus aureus and Candida albicans. A number of 25 isolates were found to be active against B. subtilis and/or to at least one of the tested indicator strains. Principal component analyses showed chemical uniqueness for four outlying bioactive actinomycetes extracts. In addition, Orthogonal Projections to Latent Structures Discriminant Analysis (OPLS-DA) and dereplication study led us to further select two outlying anti-MRSA active isolates MS.REE.13 and 22 for scale-up work. MS.REE.13 and 22 exhibited zones of inhibition at 19 and 13 mm against MRSA, respectively. A metabolomics-guided approach provided the steer to target the bioactive metabolites (P<0.01) present in a crude extract or fraction even at nanogram levels but it was a challenge that such low-yielding bioactive natural products would be feasible to isolate. Validated to occur only on the active side of OPLS-DA loadings plot, the isolated compounds exhibited medium to weak antibiotic activity with MIC values between 250 and 800 μM. Two new compounds, P_24306 (C₁₀H₁₃N₂) and N_12799 (C₁₈H₃₂O₃) with MICs of 795 and 432 μM, were afforded from the scale-up of MS.REE. 13 and 22, respectively.

Diversity of PKS and NRPS gene clusters between Streptomyces abyssomicinicus sp. nov. and its taxonomic neighbor

Streptomyces sp. CHI39, isolated from a rock soil sample, is a producer of abyssomicin I. The taxonomic status was clarified by a polyphasic approach. Phylogenetic analysis based on 16S rRNA gene sequences showed that the strain was closely related to Streptomyces fragilis, with similarity of 99.9%. Strain CHI39 comprised LL-diaminopimelic acid, glutamic acid, glycine, and alanine in its peptidoglycan. The predominant menaquinones were MK-9(H₆), and major fatty acids were anteiso-C_15:0, anteiso-C_17:0, and iso-C_16:0. The chemotaxonomic features matched those described for the genus Streptomyces. Genome sequencing was conducted for strain CHI39 and S. fragilis NBRC 12862^T. The results of digital DNA-DNA hybridization along with differences in phenotypic characteristics between the strains suggested strain CHI39 to be a novel species, for which Streptomyces abyssomicinicus sp. nov. is proposed; the type strain is CHI39^T (=NBRC 110469^T). Next, we surveyed polyketide synthase (PKS) and nonribosomal peptide synthetase (NRPS) gene clusters in genomes of S. abyssomicinicus CHI39^T and S. fragilis NBRC 12862^T. These strains encoded 9 and 12 clusters, respectively, among which only four clusters were shared between them while the others are specific in each strain. This suggests that strains classified to distinct species each harbor many specific secondary metabolite-biosynthetic pathways even if the strains are taxonomically close.

Antarctic sponges from the Terra Nova Bay (Ross Sea) host a diversified bacterial community

Sponges represent important habitats for a community of associated (micro)organisms. Even if sponges dominate vast areas of the Antarctic shelves, few investigations have been performed on Antarctic sponge-associated bacteria. Using a culture-dependent approach, the composition of the bacterial communities associated with 14 Antarctic sponge species from different sites within the Terra Nova Bay (Ross Sea) area was analyzed. Overall, isolates were mainly affiliated to Gammaproteobacteria, followed by Actinobacteria and CF group of Bacteroidetes, being the genera Pseudoalteromonas, Arthrobacter and Gillisia predominant, respectively. Alphaproteobacteria and Firmicutes were less represented. Cluster analyses highlighted similarities/differences among the sponge-associated bacterial communities, also in relation to the sampling site. The gammaproteobacterial Pseudoalteromonas sp. SER45, Psychrobacter sp. SER48, and Shewanella sp. SER50, and the actinobacterial Arthrobacter sp. SER44 phylotypes occurred in association with almost all the analyzed sponge species. However, except for SER50, these phylotypes were retrieved also in seawater, indicating that they may be transient within the sponge body. The differences encountered within the bacterial communities may depend on the different sites of origin, highlighting the importance of the habitat in structuring the composition of the associated bacterial assemblages. Our data support the hypothesis of specific ecological interactions between bacteria and Porifera.

Diversity and Distribution of Bacteria Producing Known Secondary Metabolites

There is an increasing interest in the utilisation of marine bioactive compounds as novel biopharmaceuticals and agrichemicals; however, little is known about the environmental distribution for many of these molecules. Here, we aimed to elucidate the environmental distribution and to detect the biosynthetic gene clusters in environmental samples of four bioactive compounds, namely violacein, tropodithietic acid (TDA), tambjamine and the antibacterial protein AlpP. Our database analyses revealed high bacterial diversity for AlpP and violacein producers, while TDA-producing bacteria were mostly associated with marine surfaces and all belonged to the roseobacter group. In contrast, the tambjamine cluster was only found in the genomes of two Pseudoalteromonas species and in one terrestrial species belonging to the Cupriavidus genus. Using a PCR-based screen of different marine samples, we detected TDA and violacein genes associated with the microbiome of Ulva and Protohyale niger and tambjamine genes associated with Nodilittorina unifasciata; however, alpP was not detected. These results highlight the variable distribution of the genes encoding these four bioactive compounds, including their detection from the surface of multiple marine eukaryotic hosts. Determining the natural distribution of these gene clusters will help to understand the ecological importance of these metabolites and the bacteria that produce them.

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.

Antibacterial Salinaphthoquinones from a Strain of the Bacterium Salinispora arenicola Recovered from the Marine Sediments of St. Peter and St. Paul Archipelago, Brazil

Salinaphthoquinones A-E (1-5) were isolated from a marine Salininispora arenicola strain, recovered from sediments of the St. Peter and St. Paul Archipelago, Brazil. The structures of the compounds were elucidated using a combination of spectroscopic (NMR, IR, HRESIMS) data, including single-crystal X-ray diffraction analysis. A plausible biosynthetic pathway for 1-5 is proposed. Compounds 1 to 4 displayed moderate activity against Staphylococcus aureus and Enterococcus faecalis with MIC values of 125 to 16 μg/mL.

Iron(III)-Mediated Bicyclization of 1,2-Allenyl Aryl Ketones: Assembly of Indanone-Fused Polycyclic Scaffolds and Dibenzo[a,e]pentalene Derivatives

The rapid construction of three-dimensional fused carbocycles is a key challenge in synthetic chemistry. Herein, an unprecedented and practical tandem Nazarov/oxidative umpolung 4π-ring closure of readily available 1,2-allenyl aryl ketones mediated by iron(III) chloride has been developed, furnishing a new family of indanone-fused molecular architectures in moderate to excellent yields. The indanone-containing blocks can be efficiently converted to unsymmetrical dibenzo[a,e]pentalenes. Significantly, divergent synthetic applications have been achieved to provide densely functionalized polycyclic arrays.

AutoMLST: an automated web server for generating multi-locus species trees highlighting natural product potential

Understanding the evolutionary background of a bacterial isolate has applications for a wide range of research. However generating an accurate species phylogeny remains challenging. Reliance on 16S rDNA for species identification currently remains popular. Unfortunately, this widespread method suffers from low resolution at the species level due to high sequence conservation. Currently, there is now a wealth of genomic data that can be used to yield more accurate species designations via modern phylogenetic methods and multiple genetic loci. However, these often require extensive expertise and time. The Automated Multi-Locus Species Tree (autoMLST) was thus developed to provide a rapid 'one-click' pipeline to simplify this workflow at: https://automlst.ziemertlab.com. This server utilizes Multi-Locus Sequence Analysis (MLSA) to produce high-resolution species trees; this does not preform multi-locus sequence typing (MLST), a related classification method. The resulting phylogenetic tree also includes helpful annotations, such as species clade designations and secondary metabolite counts to aid natural product prospecting. Distinct from currently available web-interfaces, autoMLST can automate selection of reference genomes and out-group organisms based on one or more query genomes. This enables a wide range of researchers to perform rigorous phylogenetic analyses more rapidly compared to manual MLSA workflows.