Unveiling the bioactive potential of Actinomycetota from the Tagus River estuary.

The increase in global travel and the incorrect and excessive use of antibiotics has led to an unprecedented rise in antibiotic resistance in bacterial and fungal populations. To overcome these problems, novel bioactive natural products must be discovered, which may be found in underexplored environments, such as estuarine habitats. In the present work, estuarine actinomycetotal strains were isolated with conventional and iChip techniques from the Tagus estuary in Alcochete, Portugal, and analysed for different antimicrobial bioactivities. Extracts were produced from the isolated cultures and tested for bioactivity against Staphylococcus aureus ATCC 29213, Escherichia coli ATCC 25922, Aspergillus fumigatus ATCC 240305, Candida albicans ATCC 10231 and Trichophyton rubrum FF5. Furthermore, bioactive extracts were subjected to dereplication by high-performance liquid chromatography (HPLC) and high-resolution mass spectrometry (HRMS) to putatively identify their chemical components. In total, 105 isolates belonging to 3 genera were obtained. One which was isolated, MTZ3.1 T, represents a described novel taxon for which the name Streptomyces meridianus was proposed. Regarding the bioactivity testing, extracts from 12 strains proved to be active against S. aureus, 2 against E. coli, 4 against A. fumigatus, 3 against C. albicans and 10 against T. rubrum. Dereplication of bioactive extracts showed the presence of 28 known bioactive molecules, 35 hits have one or more possible matches in the DNP and 18 undescribed ones. These results showed that the isolated bacteria might be the source of new bioactive natural products.

Highly Concentrated Linear Guanidine Amides from the Marine Sipunculid Phascolosoma granulatum.

The chemical diversity of annelids, particularly those belonging to the class Sipuncula, remains largely unexplored. However, as part of a Marine Biodiscovery program in Ireland, the peanut worm Phascolosoma granulatum emerged as a promising source of unique metabolites. The purification of the MeOH/CH2Cl2 extract of this species led to the isolation of six new linear guanidine amides, named phascolosomines A-F (1-6). NMR analysis allowed for the elucidation of their structures, all of which feature a terminal guanidine, central amide linkage, and a terminal isobutyl group. Notably, these guanidine amides were present in unusually high concentrations, comprising ∼3% of the dry mass of the organism. The primary concentration of the phascolosomines in the viscera is similar to that previously identified in linear amides from sipunculid worms and marine fireworms. The compounds from sipunculid worms have been hypothesized to be toxins, while those from fireworms are reported to be defensive irritants. However, screening of the newly isolated compounds for inhibitory bioactivity showed no significant inhibition in any of the assays conducted.

Genome-Led Discovery of the Antibacterial Cyclic Lipopeptide Kutzneridine A and Its Silent Biosynthetic Gene Cluster from Kutzneria Species.

Genome analysis of Kutzneria sp. CA-103260 revealed a putative lipopeptide-encoding biosynthetic gene cluster (BGC) that was cloned into a bacterial artificial chromosome (BAC) and heterologously expressed in Streptomyces coelicolor M1152. As a result, a novel cyclic lipo-tetrapeptide containing two diaminopropionic acid residues and an exotic N,N-acetonide ring, kutzneridine A (1), was isolated and structurally characterized. Evaluation of the extraction conditions and isotope-labeling chemical modifications showed that the acetonide ring originated from acetone during isolation. The BGC was analyzed in silico and a biosynthetic pathway to 1 was proposed. Kutzneridine A displayed remarkable antibacterial activity against methicillin-resistant Staphylococcus aureus and vancomycin-resistant Enterococci.

Uncovering the biotechnological capacity of marine and brackish water Planctomycetota.

An appealing strategy for finding novel bioactive molecules in Nature consists in exploring underrepresented and -studied microorganisms. Here, we investigated the antimicrobial and tumoral anti-proliferative bioactivities of twenty-three marine and estuarine bacteria of the fascinating phylum Planctomycetota. This was achieved through extraction of compounds produced by the Planctomycetota cultured in oligotrophic medium followed by an antimicrobial screening against ten relevant human pathogens including Gram-positive and Gram-negative bacteria, and fungi. Cytotoxic effects of the extracts were also evaluated against five tumoral cell lines. Moderate to potent activities were obtained against Enterococcus faecalis, methicillin-sensitive and methicillin-resistant Staphylococcus aureus and vancomycin-sensitive and vancomycin-resistant Enterococcus faecium. Anti-fungal effects were observed against Trichophyton rubrum, Candida albicans and Aspergillus fumigatus. The highest cytotoxic effects were observed against human breast, pancreas and melanoma tumoral cell lines. Novipirellula caenicola and Rhodopirellula spp. strains displayed the widest spectrum of bioactivities while Rubinisphaera margarita ICM_H10T affected all Gram-positive bacteria tested. LC-HRMS analysis of the extracts did not reveal the presence of any known bioactive natural product, suggesting that the observed activities are most likely caused by novel molecules, that need identification. In summary, we expanded the scope of planctomycetal species investigated for bioactivities and demonstrated that various strains are promising sources of novel bioactive compounds, which reenforces the potential biotechnological prospects offered by Planctomycetota.

Rheumatoid meningitis: a case series report and review of modern therapeutic schemes and outcome.

INTRODUCTION: Rheumatoid meningitis (RM) is an extremely rare extra-articular complication of rheumatoid arthritis (RA), with approximately 165 cases reported world-wide. RM exhibits a broad range of symptoms, with stroke-like episodes and seizures being the most common manifestations. The primary differential diagnoses include vascular and infectious diseases. The influence of immunomodulatory medications on the pathophysiology of RM remains unclear. There are no consensus guidelines on therapeutic regimen. METHODS: We present four patients with prior history of RA that developed different neurological syndromes in correlation to radiological leptomeningitis. Clinical presentations, comorbid conditions, supplementary diagnostic assessments, treatments, and prognosis are provided. A literature review of recent immunosuppressive management in RM patients was performed. RESULTS: Three patients presented to hospital with recurrent focal seizures. Only two suffered meningism, reporting headache and fever. Magnetic resonance imaging (MRI) showed different grades of leptomeningitis across all cases. Notably, three cases demonstrated bilateral involvement extending to the pachymeninges. Two patients exhibited pronounced CSF mononuclear inflammation while extended microbiological evaluations yielded negative results. Two patients required biopsy for confirmation. The initiation of immunosuppressive therapy marked a turning point for three patients who previously exhibited progressive deterioration. Mortality was absent in all cases. CONCLUSIONS: Our experience remarks the elusive nature of RM. Rigorous exclusionary diagnostics are imperative to differentiate RM from mimicking conditions. Clinical manifestations oscillate between transient episodes and progressive neurological impairments, punctuated by frequent epileptic seizures. In scenarios where clinical worsening persists or where clinical and radiological evaluations are inconclusive, aggressive immunosuppressive therapy is recommended.

Cellulamides: A New Family of Marine-Sourced Linear Peptides from the Underexplored Cellulosimicrobium Genus.

Bioprospecting the secondary metabolism of underexplored Actinomycetota taxa is a prolific route to uncover novel chemistry. In this work, we report the isolation, structure elucidation, and bioactivity screening of cellulamides A and B (1 and 2), two novel linear peptides obtained from the culture of the macroalga-associated Cellulosimicrobium funkei CT-R177. The host of this microorganism, the Chlorophyta Codium tomentosum, was collected in the northern Portuguese coast and, in the scope of a bioprospecting study focused on its associated actinobacterial community, strain CT-R177 was isolated, taxonomically identified, and screened for the production of antimicrobial and anticancer compounds. Dereplication of a crude extract of this strain using LC-HRMS(/MS) analysis unveiled a putative novel natural product, cellulamide A (1), that was isolated following mass spectrometry-guided fractionation. An additional analog, cellulamide B (2) was obtained during the chromatographic process and chemically characterized. The chemical structures of the novel linear peptides, including their absolute configurations, were elucidated using a combination of HRMS, 1D/2D NMR spectroscopy, and Marfey's analysis. Cellulamide A (1) was subjected to a set of bioactivity screenings, but no significant biological activity was observed. The cellulamides represent the first family of natural products reported from the Actinomycetota genus Cellulosimicrobium, showcasing not only the potential of less-explored taxa but also of host-associated marine strains for novel chemistry discovery.

Endocarditis in Adult Congenital Heart Disease Patients: Prevention, Recognition, and Management.

PURPOSE OF REVIEW: Present an updated overview of the prevention, diagnosis, and management of infective endocarditis in adult patients with congenital heart disease. RECENT FINDINGS: Care for patients with infective endocarditis is changing in the areas of specialized teams, diagnostics, and prevention. Endocarditis teams should be involved in the care of ACHD patients. The 2023 Duke Criteria for Infective Endocarditis and the 2023 European Society of Cardiology Guidelines have updated the criteria for diagnosis including new major criteria such as CT and positron emission computed tomography with 18F-fluorodeoxyglucose (FDG) scans. Immunological, PCR, and nucleic acid-based tests are now acceptable means to isolate infective organisms. Clindamycin is no longer recommended for antibiotic prophylaxis due to resistance and side effect profile. Special considerations for antibiotic prophylaxis and management must be made for specific congenital heart diseases in adulthood and pregnant ACHD patients. Infective endocarditis (IE), a potentially devastating clinical entity, is a feared threat to the health of adults with congenital heart disease (ACHD). IE needs a systematic approach for its prevention, early diagnosis and management with a multidisciplinary IE team's involvement. There have been changes in the diagnostics and management of IE, which is reflected in updated diagnostic criteria. Timely blood cultures and imaging continue to be the mainstay of diagnosis, however the timing of blood cultures, microbiological testing, and types of diagnostic imaging such as the positron emission computed tomography with 18F-fluorodeoxyglucose (FDG) scan are new. Bicuspid aortic valves, ventricular septal defects, transcatheter pulmonary valve replacements, and tetralogy of Fallot are diagnoses at higher risk for IE in the ACHD population. The following article will focus on the preventive strategies, in addition to novel diagnostic and therapeutic approaches of IE in ACHD patients.

Unearthing a Cryptic Biosynthetic Gene Cluster for the Piperazic Acid-Bearing Depsipeptide Diperamycin in the Ant-Dweller Streptomyces sp. CS113.

Piperazic acid is a cyclic nonproteinogenic amino acid that contains a hydrazine N-N bond formed by a piperazate synthase (KtzT-like). This amino acid, found in bioactive natural products synthesized by non-ribosomal peptide synthetases (NRPSs), confers conformational constraint to peptides, an important feature for their biological activities. Genome mining of Streptomyces strains has been revealed as a strategy to identify biosynthetic gene clusters (BGCs) for potentially active compounds. Moreover, the isolation of new strains from underexplored habitats or associated with other organisms has allowed to uncover new BGCs for unknown compounds. The in-house "Carlos Sialer (CS)" strain collection consists of seventy-one Streptomyces strains isolated from the cuticle of leaf-cutting ants of the tribe Attini. Genomes from twelve of these strains have been sequenced and mined using bioinformatics tools, highlighting their potential to encode secondary metabolites. In this work, we have screened in silico those genomes, using KtzT as a hook to identify BGCs encoding piperazic acid-containing compounds. This resulted in uncovering the new BGC dpn in Streptomyces sp. CS113, which encodes the biosynthesis of the hybrid polyketide-depsipeptide diperamycin. Analysis of the diperamycin polyketide synthase (PKS) and NRPS reveals their functional similarity to those from the aurantimycin A biosynthetic pathway. Experimental proof linking the dpn BGC to its encoded compound was achieved by determining the growth conditions for the expression of the cluster and by inactivating the NRPS encoding gene dpnS2 and the piperazate synthase gene dpnZ. The identity of diperamycin was confirmed by High-Resolution Mass Spectrometry (HRMS) and Nuclear Magnetic Resonance (NMR) and by analysis of the domain composition of modules from the DpnP PKS and DpnS NRPS. The identification of the dpn BGC expands the number of BGCs that have been confirmed to encode the relatively scarcely represented BGCs for depsipeptides of the azinothricin family of compounds and will facilitate the generation of new-to-nature analogues by combinatorial biosynthesis.

Naphthoquinone Derivatives from Angustimassarina populi CF-097565 Display Anti-Tumour Activity in 3D Cultures of Breast Cancer Cells.

Cancer is one of the leading causes of death worldwide, with breast cancer being the second cause of cancer-related mortality among women. Natural Products (NPs) are one of the main sources for drug discovery. During a screening campaign focused on the identification of extracts from Fundación MEDINA's library inhibiting the proliferation of cancer cell lines, a significant bioactivity was observed in extracts from cultures of the fungus Angustimassarina populi CF-097565. Bioassay-guided fractionation of this extract led to the identification and isolation of herbarin (1), 1-hydroxydehydroherbarin (4) plus other three naphthoquinone derivatives of which 3 and 5 are new natural products and 2 is herein described from a natural source for the first time. Four of these compounds (1, 3, 4 and 5) confirmed a specific cytotoxic effect against the human breast cancer cell line MCF-7. To evaluate the therapeutic potential of the compounds isolated, their efficacy was validated in 3D cultures, a cancer model of higher functionality. Additionally, an in-depth study was carried out to test the effect of the compounds in terms of cell mortality, sphere disaggregation, shrinkage, and morphology. The cell profile of the compounds was also compared to that of known cytotoxic compounds with the aim to distinguish the drug mode of action (MoA). The profiles of 1, 3 and 4 showed more biosimilarity between them, different to 5, and even more different to other known cytotoxic agents, suggesting an alternative MoA responsible for their cytotoxicity in 3D cultures.

Streptomyces meridianus sp. nov. isolated from brackish water of the Tagus estuary in Alcochete, Portugal.

An isolation effort focused on sporogenous Actinomycetota from the Tagus estuary in Alcochete, Portugal, yielded a novel actinomycetal strain, designated MTZ3.1T, which was subjected to a polyphasic taxonomic study. MTZ3.1T is characterised by morphology typical of members of the genus Streptomyces, with light beige coloured substrate mycelium, which does not release pigments to the culture medium and with helicoidal aerial hyphae that differentiate into spores with a light-grey colour. The phylogeny of MTZ3.1T, based on the full 16S rRNA gene sequence, indicated that its closest relatives were Streptomyces alkaliterrae OF1T (98.48 %), Streptomyces chumphonensis KK1-2T (98.41 %), Streptomyces albofaciens JCM 4342T (98.34 %), Streoptomyces paromomycinus NBRC 15454T (98.34 %) and Streptomyces chrestomyceticus NRBC 13444T (98.34 %). Moreover, average nucleotide identity (ANI), average amino acid identity (AAI) and digital DNA-DNA hybridisation (dDDH) are below the species cutoff values (ANI 67.70 and 68.35 %, AAI 77.06 and 76.71 % and dDDH 22.10 and 21.50 % for S. alkaliterrae OF1T and S. chumphonensis KK1-2T, respectively). Whole genome sequencing revealed that MTZ3.1T has a genome of 5 644 485 bp with a DNA G+C content of 71.29 mol% and 5044 coding sequences. Physiologically, MTZ3.1T is strictly aerobic, able to grow at 15-37 °C, optimally at 25 °C and between pH5 and 8 and showed high salinity tolerance, growing with 0-10 %(w/v) NaCl. Major cellular fatty acids are C15 : 0, iso-C15 : 0, anteiso-C15 : 0 and iso-C16 : 0. Furthermore, it was able to utilise a variety of nitrogen and carbon sources. Antimicrobial screening indicated that MTZ3.1T has potent anti-Staphylococcus aureus activity. On the basis of the polyphasic data, MTZ3.1T is proposed to represent a novel species, Streptomyces meridianus sp. nov. (= CECT 30416T = DSM 114037T=LMG 32463T).

Streptomyces marispadix sp. nov., isolated from marine beach sediment.

A novel actinomycetal strain, designated M600PL45_2T, was isolated from marine sediments obtained from Ingleses beach, Porto, on the Northern Coast of Portugal and was subjected to a polyphasic taxonomic characterisation study. The here described Gram-reaction-positive strain is characterised by the production of a brown pigment in both solid and liquid medium and forms typical helical hyphae that differentiate into smooth spores. The results of a phylogenetic analysis based on the 16S rRNA gene sequence indicated that M600PL45_2T has a high similarity to two members of the genus Streptomyces, Streptomyces bathyalis ASO4wetT (98.51 %) and Streptomyces daqingensis NEAU ZJC8T (98.44 %). The genome of M600PL45_2T has a size of 6 695 159 bp, a DNA G+C content of 70.71 mol% and 5538 coding sequences. M600PL45_2T grows at 15-37 °C and with a maximal growth rate between 25 °C and 30 °C. Growth at pH 6.0 to 9.0 with the optimal range between 6.0 and 7.5 was observed. M600PL45_2T showed a high salinity tolerance, growing with 0-10 % (w/v) NaCl, with best growth with 1-3% (w/v) NaCl. Major cellular fatty acids are iso-C15:0 (25.03 %), anteiso-C15:0 (17.70) and iso-C16:0 (26.90 %). The novel isolate was able to grow in media containing a variety of nitrogen and carbon sources. An antimicrobial activity screening indicated that an extract of M600PL45_2T has inhibitory activity against Staphylococcus aureus. On the basis of the polyphasic data, M600PL45_2T (= CECT 30365T = DSM 114036T) is introduced as the type strain of a novel species, that we named Streptomyces marispadix sp. nov.

Additional Sarasinosides from the Marine Sponge Melophlus sarasinorum Collected from the Bismarck Sea.

In our continuing efforts to describe the biological and chemical diversity of sponges from Kimbe Bay, Papua New Guinea, the known 30-norlanostane saponin sarasinoside C1 (1) was identified along with six new analogues named sarasinosides C4, C5, C6, C7, C8, and C9 (2-7) from the sponge Melophlus sarasinorum. The structures of the new compounds were elucidated by analysis of 1D and 2D NMR and HRMS data, as well as comparison with literature data. All new compounds are characterized by the same tetraose moiety, ß-d-Xylp-(1→6)-ß-d-GlcNAcp-(1→2)-[ß-d-GalNAcp-(1→4)]-ß-d-Xylp, as described previously for sarasinoside C1, but differed in their aglycone moieties. When comparing NMR data of sarasinoside C8 with those of known analogues, a misassignment was identified in the configuration of the C-8/C-9 diol for the previously described sarasinoside R (8), and it has been corrected here using a combination of ROESY analysis and molecular modeling.

Advanced Methods for Natural Products Discovery: Bioactivity Screening, Dereplication, Metabolomics Profiling, Genomic Sequencing, Databases and Informatic Tools, and Structure Elucidation.

Natural Products (NP) are essential for the discovery of novel drugs and products for numerous biotechnological applications. The NP discovery process is expensive and time-consuming, having as major hurdles dereplication (early identification of known compounds) and structure elucidation, particularly the determination of the absolute configuration of metabolites with stereogenic centers. This review comprehensively focuses on recent technological and instrumental advances, highlighting the development of methods that alleviate these obstacles, paving the way for accelerating NP discovery towards biotechnological applications. Herein, we emphasize the most innovative high-throughput tools and methods for advancing bioactivity screening, NP chemical analysis, dereplication, metabolite profiling, metabolomics, genome sequencing and/or genomics approaches, databases, bioinformatics, chemoinformatics, and three-dimensional NP structure elucidation.

New Phocoenamicin and Maklamicin Analogues from Cultures of Three Marine-Derived Micromonospora Strains.

Antimicrobial resistance can be considered a hidden global pandemic and research must be reinforced for the discovery of new antibiotics. The spirotetronate class of polyketides, with more than 100 bioactive compounds described to date, has recently grown with the discovery of phocoenamicins, compounds displaying different antibiotic activities. Three marine Micromonospora strains (CA-214671, CA-214658 and CA-218877), identified as phocoenamicins producers, were chosen to scale up their production and LC/HRMS analyses proved that EtOAc extracts from their culture broths produce several structurally related compounds not disclosed before. Herein, we report the production, isolation and structural elucidation of two new phocoenamicins, phocoenamicins D and E (1-2), along with the known phocoenamicin, phocoenamicins B and C (3-5), as well as maklamicin (7) and maklamicin B (6), the latter being reported for the first time as a natural product. All the isolated compounds were tested against various human pathogens and revealed diverse strong to negligible activity against methicillin-resistant Staphylococcus aureus, Mycobacterium tuberculosis H37Ra, Enterococcus faecium and Enterococcus faecalis. Their cell viability was also evaluated against the human liver adenocarcinoma cell line (Hep G2), demonstrating weak or no cytotoxicity. Lastly, the safety of the major compounds obtained, phocoenamicin (3), phocoenamicin B (4) and maklamicin (7), was tested against zebrafish eleuthero embryos and all of them displayed no toxicity up to a concentration of 25 µM.

Interactions of Different Streptomyces Species and Myxococcus xanthus Affect Myxococcus Development and Induce the Production of DK-Xanthenes.

The co-culturing of microorganisms is a well-known strategy to study microbial interactions in the laboratory. This approach facilitates the identification of new signals and molecules produced by one species that affects other species' behavior. In this work, we have studied the effects of the interaction of nine Streptomyces species (S. albidoflavus, S. ambofaciens, S. argillaceus, S. griseus, S. lividans, S. olivaceus, S. parvulus, S. peucetius, and S. rochei) with the predator bacteria Myxococcus xanthus, five of which (S. albidoflavus, S. griseus, S. lividans, S. olivaceus, and S. argillaceus) induce mound formation of M. xanthus on complex media (Casitone Yeast extract (CYE) and Casitone tris (CTT); media on which M. xanthus does not form these aggregates under normal culture conditions. An in-depth study on S. griseus-M. xanthus interactions (the Streptomyces strain producing the strongest effect) has allowed the identification of two siderophores produced by S. griseus, demethylenenocardamine and nocardamine, responsible for this grouping effect over M. xanthus. Experiments using pure commercial nocardamine and different concentrations of FeSO4 show that iron depletion is responsible for the behavior of M. xanthus. Additionally, it was found that molecules, smaller than 3 kDa, produced by S. peucetius can induce the production of DK-xanthenes by M. xanthus.

Uncovering the Cryptic Gene Cluster ahb for 3-amino-4-hydroxybenzoate Derived Ahbamycins, by Searching SARP Regulator Encoding Genes in the Streptomyces argillaceus Genome.

Genome mining using standard bioinformatics tools has allowed for the uncovering of hidden biosynthesis gene clusters for specialized metabolites in Streptomyces genomes. In this work, we have used an alternative approach consisting in seeking "Streptomyces Antibiotic Regulatory Proteins" (SARP) encoding genes and analyzing their surrounding DNA region to unearth cryptic gene clusters that cannot be identified using standard bioinformatics tools. This strategy has allowed the unveiling of the new ahb cluster in Streptomyces argillaceus, which had not been retrieved before using antiSMASH. The ahb cluster is highly preserved in other Streptomyces strains, which suggests a role for their encoding compounds in specific environmental conditions. By combining overexpression of three regulatory genes and generation of different mutants, we were able to activate the ahb cluster, and to identify and chemically characterize the encoded compounds that we have named ahbamycins (AHBs). These constitute a new family of metabolites derived from 3-amino-4-hydroxybenzoate (3,4-AHBA) known for having antibiotic and antitumor activity. Additionally, by overexpressing three genes of the cluster (ahbH, ahbI, and ahbL2) for the synthesis and activation of 3,4-AHBA, a new hybrid compound, AHB18, was identified which had been produced from a metabolic crosstalk between the AHB and the argimycin P pathways. The identification of this new BGC opens the possibility to generate new compounds by combinatorial biosynthesis.

Madurastatins with Imidazolidinone Rings: Natural Products or Side-Reaction Products from Extraction Solvents?

Madurastatins are a group of pentapeptides containing an oxazoline moiety, and, in a few cases, an imidazolidinone ring as an additional structural feature. In our search for new potential antiparasitic metabolites from natural sources, we studied the acetone extracts from a culture of Actinomadura sp. CA-135719. The LC/HRMS analysis of this extract identified the presence of the known madurastatins C1 (1), D1 (4), and D2 (5) together with additional members of the family that were identified as the new madurastatins H2 (2) and 33-epi-D1 (3) after isolation and spectroscopic analysis. The planar structures of the new compounds were established by HRMS, ESI-qTOF-MS/MS, and 1D and 2D NMR data, and their absolute configuration was proposed using Marfey's and bioinformatic analyses of the biosynthetic gene cluster (BGC). A revision of the absolute configuration of madurastatins D1 and D2 is proposed. Additionally, madurastatins containing imidazolidinone rings are proved to be artifacts originating during acetone extraction of the bacterial cultures.

Colibrimycins, Novel Halogenated Hybrid Polyketide Synthase-Nonribosomal Peptide Synthetase (PKS-NRPS) Compounds Produced by Streptomyces sp. Strain CS147.

The improvement of genome sequencing techniques has brought to light the biosynthetic potential of actinomycetes due to the large number of gene clusters they present compared to the number of known compounds. Genome mining is a recent strategy in the search for novel bioactive compounds, which involves the analysis of sequenced genomes to identify uncharacterized natural product biosynthetic gene clusters, many of which are cryptic or silent under laboratory conditions, and to develop experimental approaches to identify their products. Owing to the importance of halogenation in terms of structural diversity, bioavailability, and bioactivity, searching for new halogenated bioactive compounds has become an interesting issue in the field of natural product discovery. Following this purpose, a screening for halogenase coding genes was performed on 12 Streptomyces strains isolated from fungus-growing ants of the Attini tribe. Using the bioinformatics tools antiSMASH and BLAST, six halogenase coding genes were identified. Some of these genes were located within biosynthetic gene clusters (BGCs), which were studied by construction of several mutants for the identification of the putative halogenated compounds produced. The comparison of the metabolite production profile of wild-type strains and their corresponding mutants by ultrahigh-performance liquid chromatography-UV and high-performance liquid chromatography-mass spectrometry allowed us the identification of a novel family of halogenated compounds in Streptomyces sp. strain CS147, designated colibrimycins. IMPORTANCE Genome mining has proven its usefulness in the search for novel bioactive compounds produced by microorganisms, and halogenases comprise an interesting starting point. In this work, we have identified a new halogenase coding gene that led to the discovery of novel lipopetide nonribosomal peptide synthetase/polyketide synthase (NRPS/PKS)-derived natural products, the colibrimycins, produced by Streptomyces sp. strain CS147, isolated from the Attini ant niche. Some colibrimycins display an unusual α-ketoamide moiety in the peptide structure. Although its biosynthetic origin remains unknown, its presence might be related to a hypothetical inhibition of virus proteases, and, together with the presence of the halogenase, it represents a feature to be incorporated in the arsenal of structural modifications available for combinatorial biosynthesis.

Antifungal mono- and dimeric nitrogenous bisabolene derivatives from a sponge in the order Bubarida from Futuna Islands.

An abundant sponge of the order Bubarida was selected for further chemical investigation following biological and chemical screening of sponges collected from Futuna Islands in the Indo-Pacific. Ten new nitrogenous bisabolene derivatives were isolated and identified: the monomeric theonellin formamide analogues named bubaridins A-F (1-6) with unusual oxidised linear chains, and the first isocyanide/formamide dimeric and cyclised bisabolenes 7-9. The structure elucidation of these nitrogenous bisabolenes involved HRESIMS, NMR, and ECD analyses, and the chiral compounds were found to be racemates. A biosynthetic hypothesis for the production of these metabolites is proposed and some chemotaxonomic considerations are discussed. Furthermore, the antimicrobial and antitumoral activity were evalutated and the trans-dimer theonellin isocyanide (7) was shown to exhibit potent and selective antifungal activity.

Expanding the utility of Marfey's analysis by using HPLC-SPE-NMR to determine the Cß configuration of threonine and isoleucine residues in natural peptides.

The determination of amino acid chirality in natural peptides is typically addressed by Marfey's analysis. This approach relies on the complete hydrolysis of the peptide followed by the reaction of the resulting amino acid pool with Marfey's reagent, a chiral derivatizing agent which turns amino acid enantiomers into diastereomeric pairs which can be resolved by conventional reversed-phase HPLC. However, for certain amino acids possessing a second chiral centre at Cß, the discrimination between the two possible epimers may still be challenging due to the lack of chromatographic resolution. Such is the case of isoleucine and threonine which can also be found in natural nonribosomal peptides as their allo-diastereomers. We describe a new approach based on the extension of Marfey's analysis using HPLC-SPE-NMR to sort out this challenge. Marfey's derivatives of these epimeric amino acids at Cß can be differentiated by their distinct NMR spectra. Thus, simple comparison of the NMR spectra of trapped HPLC peaks with the corresponding spectra of standards enables the unambiguous assignment of the absolute configuration at the second chiral centre in such cases. The general applicability of this approach is showcased for two model cyclic peptides bearing L-Ile and L-Thr.