Dithiolopyrrolone antibiotic formation induced by adding valeric acid to the culture broth of Saccharothrix algeriensis

Access to thiionized-, selenolized-, and alkylated 5-alkylidene 3-pyrrolin-2-one derivatives via a regioselective oxidative annulation reaction

A metal-free regioselective oxidative annulation reaction of readily available 2,4-pentanediones with primary amines has been described. This protocol provides a divergent strategy for the incorporation of various radical donors into 5-alkylidene 3-pyrrolin-2-one skeletons, producing a variety of thiionized-, selenolized-, and alkylated 5-alkylidene 3-pyrrolin-2-one derivatives. Moreover, the diverse synthetic transformations of the 5-alkylidene 3-pyrrolin-2-one products were also investigated.

Efficacy of Saccharothrix algeriensis NRRL B-24137 to suppress Fusarium oxysporum f.sp. vasinfectum induced wilt disease in cotton

Fusarium cotton wilt is a devastating disease of the cotton crop throughout the world, caused by Fusarium oxysporum f.sp. vasinfectum (FOV). Chemical control has many side effects, so, biological controls have been widely used for the management of Fusarium wilt. This study aimed to investigate the possible use of an actinomycetes Saccharothrix algeriensis (SA) NRRL B-24137 to control FOV. To access in-vitro anti-Fusarium ability of SA NRRL B-24137, dual culture assay, spore germination and seed germination tests were carried out. Following in-vitro investigations, several pot tests in a greenhouse environment were used to evaluate the biological control potential of SA NRRL B-24137 against FOV. Dual culture assay and spore germination revealed that SA NRRL B-24137 showed significant anti-Fusarium activity.During spore germination 87.77% inhibition of spore germination were observed. In pot experiments, SA NRRL B-24137 primed cotton seeds resulted in a 74.0% reduction in disease incidence. In soil there was a significant reduction in FOV spores in the presence of SA NRRL B-24137. Positive correlation was also observed on different concentrations of SA NRRL B-24137 towards FOV reduction. The results of this study showed that SA NRRL B-24137 has the potential to be employed as a biocontrol agent against Fusarium cotton wilt, improving cotton growth characteristics and yield.

Facile approach to multifunctionalized 5-alkylidene-3-pyrrolin-2-ones via regioselective oxidative cyclization of 2,4-pentanediones with primary amines and sodium sulfinates

Highly functionalized 5-alkylidene-3-pyrrolin-2-ones were efficiently synthesized via a four-component cascade cyclization/sulfonylation reaction between readily available 2,4-pentanediones, primary amines and sodium sulfinates under mild conditions.

Whole-genome sequencing of two Streptomyces strains isolated from the sand dunes of Sahara

BACKGROUND

Sahara is one of the largest deserts in the world. The harsh climatic conditions, especially high temperature and aridity lead to unique adaptation of organisms, which could be a potential source of new metabolites. In this respect, two Saharan soils from El Oued Souf and Beni Abbes in Algeria were collected. The bacterial isolates were selected by screening for antibacterial, antifungal, and enzymatic activities. The whole genomes of the two native Saharan strains were sequenced to study desert Streptomyces microbiology and ecology from a genomic perspective.

RESULTS

Strains Babs14 (from Beni Abbes, Algeria) and Osf17 (from El Oued Souf, Algeria) were initially identified by 16S rRNA sequencing as belonging to the Streptomyces genus. The whole genome sequencing of the two strains was performed using Pacific Biosciences Sequel II technology (PacBio), which showed that Babs14 and Osf17 have a linear chromosome of 8.00 Mb and 7.97 Mb, respectively. The number of identified protein coding genes was 6910 in Babs14 and 6894 in Osf17. No plasmids were found in Babs14, whereas three plasmids were detected in Osf17. Although the strains have different phenotypes and are from different regions, they showed very high similarities at the DNA level. The two strains are more similar to each other than either is to the closest database strain. The search for potential secondary metabolites was performed using antiSMASH and predicted 29 biosynthetic gene clusters (BGCs). Several BGCs and proteins were related to the biosynthesis of factors needed in response to environmental stress in temperature, UV light and osmolarity.

CONCLUSION

The genome sequencing of Saharan Streptomyces strains revealed factors that are related to their adaptation to an extreme environment and stress conditions. The genome information provides tools to study ecological adaptation in a desert environment and to explore the bioactive compounds of these microorganisms. The two whole genome sequences are among the first to be sequenced for the Streptomyces genus of Algerian Sahara. The present research was undertaken as a first step to more profoundly explore the desert microbiome.

Bioprospecting of Soil-Derived Actinobacteria Along the Alar-Hotan Desert Highway in the Taklamakan Desert

Taklamakan desert is known as the largest dunefield in China and as the second largest shifting sand desert in the world. Although with long history and glorious culture, the Taklamakan desert remains largely unexplored and numerous microorganisms have not been harvested in culture or taxonomically identified yet. The main objective of this study is to explore the diversity, novelty, and pharmacological potential of the cultivable actinomycetes from soil samples at various sites along the Alar-Hotan desert highway in the Taklamakan desert. A total of 590 actinobacterial strains were recovered by the culture-dependent approach. Phylogenetic analysis based on 16S ribosomal RNA (rRNA) gene sequences unveiled a significant level of actinobacterial diversity with 55 genera distributed in 27 families of 12 orders. Thirty-six strains showed relatively low 16S rRNA similarities (<98.65%) with validly described species, among which four strains had already been characterized as novel taxa by our previous research. One hundred and forty-six actinobacterial isolates were selected as representatives to evaluate the antibacterial activities and mechanism of action by the paper-disk diffusion method and a double fluorescent protein reporter "pDualrep2" system, respectively. A total of 61 isolates exhibited antagonistic activity against the tested "ESKAPE" pathogens, among which seven strains could produce bioactive metabolites either to be able to block translation machinery or to induce SOS-response in the pDualrep2 system. Notably, Saccharothrix sp. 16Sb2-4, harboring a promising antibacterial potential with the mechanism of interfering with protein translation, was analyzed in detail to gain deeper insights into its bioactive metabolites. Through ultra-performance liquid chromatography (UPLC)-quadrupole time-of-flight (QToF)-MS/MS based molecular networking analysis and databases identification, four families of compounds (1-16) were putatively identified. Subsequent bioassay-guided separation resulted in purification of four 16-membered macrolide antibiotics, aldgamycin H (8), aldgamycin K (9), aldgamycin G (10), and swalpamycin B (11), and their structures were elucidated by HR-electrospray ionization source (ESI)-MS and NMR spectroscopy. All compounds 8-11 displayed antibacterial activities by inhibiting protein synthesis in the pDualrep2 system. In conclusion, this work demonstrates that Taklamakan desert is a potentially unique reservoir of versatile actinobacteria, which can be a promising source for discovery of novel species and diverse bioactive compounds.

Saccharothrix Algeriensis NRRL B-24137 Potentiates Chemical Fungicide Carbendazim in Treating Fusarium Oxysporum f.sp. Vasinfectum-Induced Cotton Wilt Disease

Cotton (Gossypium hirsutum) wilt is one of the destructive disease caused by Fusarium oxysporum f. sp. vasinfectum and lead to 100% yield loss under favorable conditions. This study aims to estimate the potential of biological control agents Saccharothrix algeriensis NRRL B-24137 (SA) and chemical fungicides against cotton wilt pathogen under in-vitro and in-vivo conditions. The in-vitro study revealed that carbendazim showed maximum mycelia growth inhibition with a mean of 91% over control, which was further validated in glasshouse assay. In-vitro dual culture test of biocontrol agents with F. oxysporum determined that SA had a potential to inhibit mycelia growth by 68% compared to control. Further in glasshouse assay, the combination of the SA and carbendazim (10 µg/mL) showed a significant (p < 0.05) disease control. Moreover, results demonstrated that carbendazim and SA remarkably decreased the disease development up to 83% and subsequently, significant improvement was observed in the plant growth parameters (plant length, root length, and plant weight) compared to untreated plants. Conclusively, exploration and utilization of bioagent for fungal diseases in cotton may provide a better line with maximum efficacy and with lesser adverse effects, which will pave a way toward better consequences in fungal treatments.

Mzabimycins A and B, novel intracellular angucycline antibiotics produced by Streptomyces sp. PAL114 in synthetic medium containing L-tryptophan

In our previous studies, the production of four bioactive molecules by Streptomyces sp. PAL114 in complex ISP2 broth medium has been described. Three of these molecules belong to the angucycline family. In this study, two novel antibiotics belonging to the same family were produced by strain PAL114 on M2 synthetic medium containing L-tryptophan as precursor. These antibiotics, named mzabimycins A and B, were intracellular and produced only in the presence of L-tryptophan. After four days of culturing PAL114 in the M2 medium, the bioactive compounds were extracted from mycelium with methanol and then analyzed by HPLC on reverse phase C18 column. Two active purplish blue fractions were purified. The chemical structures of these molecules were determined on the basis of spectroscopic and spectrometric analyses (1H and 13C NMR, and mass spectra). They were identified to be novel angucycline derivative antibiotics. The pure molecules showed activity against some pathogenic Gram-positive bacteria which have multiple antibiotic resistance, such as Staphylococcus aureus MRSA 639c and Listeria monocytogenes ATCC 13932.

Actinobacteria Derived from Algerian Ecosystems as a Prominent Source of Antimicrobial Molecules

Actinobacteria, in particular "rare actinobacteria" isolated from extreme ecosystems, remain the most inexhaustible source of novel antimicrobials, offering a chance to discover new bioactive metabolites. This is the first overview on actinobacteria isolated in Algeria since 2002 to date with the aim to present their potential in producing bioactive secondary metabolites. Twenty-nine new species and one novel genus have been isolated, mainly from the Saharan soil and palm groves, where 37.93% of the most abundant genera belong to Saccharothrix and Actinopolyspora. Several of these strains were found to produce antibiotics and antifungal metabolites, including 17 new molecules among the 50 structures reported, and some of these antibacterial metabolites have shown interesting antitumor activities. A series of approaches used to enhance the production of bioactive compounds is also presented as the manipulation of culture media by both classical methods and modeling designs through statistical strategies and the associations with diverse organisms and strains. Focusing on the Algerian natural sources of antimicrobial metabolites, this work is a representative example of the potential of a closely combined study on biology and chemistry of natural products.

A new dithiolopyrrolone antibiotic triggered by a long fermentation of Saccharothrix algeriensis NRRL B-24137 in sorbic acid-amended medium

Saccharothrix algeriensis NRRL B-24137 is an actinobacterium isolated from Algerian Saharan soil. It produces bioactive compounds belonging to the dithiolopyrrolone class of antibiotics, which are characterized by the possession of a unique pyrrolinonodithiole nucleus. Dithiolopyrrolones are known for their strong antibacterial and antifungal activities. This class of antibiotics generated great interest after the discovery of their anticancer properties. In this study, an antibiotic named PR11, produced after a long bacterial fermentation (11 days) in sorbic acid-containing culture broth, was characterized as a new dithiolopyrrolone derivative. After HPLC analysis and purification, the chemical structure of this antibiotic was determined by ¹ H- and ¹³ C-nuclear magnetic resonance, mass and UV-visible data. PR11 was thus characterized as an iso-hexanoyl-pyrrothine, a novel dithiolopyrrolone derivative. The minimum inhibitory concentrations of the new induced antibiotic were determined against several pathogenic micro-organisms. A moderate to strong activity was noted against all Gram-positive bacteria, filamentous fungi and yeasts tested. SIGNIFICANCE AND IMPACT OF THE STUDY: Given the strong activities of dithiolopyrrolones against diverse prokaryotic and eukaryotic micro-organisms including potent selective-anticancer activity, the discovery of new-related derivatives draw continuous attention for therapeutic research. Depending on nature and concentration of added precursor, Saccharothrix algeriensis NRRL B-24137 produce several dithiolopyrrolone coumpounds. In this study, sorbic acid addition combined to long fermentation duration was shown to induce the biosynthesis of a novel dithiolopyrrolone derivative. After purification and full spectroscopic and spectrometric study, the compound was characterized as iso-hexanoyl-pyrrothine. In the future investigation for novel dithiolopyrrolone discovery, fermentation duration should be regarded as a key parameter as well.

Effective biosynthesis of benzoyl-pyrrothine dithiolopyrrolone antibiotic by cinnamic acid-precursor addition in culture of Saccharothrix algeriensis NRRL B-24137

Dithiolopyrrolone antibiotics, produced by several micro-organisms, are known for their strong antimicrobial and antitumor activities. Among of this micro-organisms, Saccharothrix algeriensis NRRL B-24137, a rare actinobacterium, has the ability to produce several dithiolopyrrolones derivatives depending on precursors added in the culture medium. After 10 days of strain fermentation on semi-synthetic medium supplemented with cinnamic acid and HPLC purification, biosynthesis of benzoyl-pyrrothine dithiolopyrrolone was evidenced through complete spectroscopic (UV-visible and 1H and 13C NMR) and spectrometric (electron impact mass spectrum) analyses. The pure molecule showed appreciable minimum inhibitory concentration values against several Gram-positive bacteria and filamentous fungi. SIGNIFICANCE AND IMPACT OF THE STUDY: Dithiolopyrrolone antibiotics, known for their strong antimicrobial activities, gained greater interest after the discovery of their antitumor properties. Depending on precursors added, Saccharothrix algeriensis NRRL B-24137 has the ability to produce several dithiolopyrrolones derivatives. Since biological activities of dithiolopyrrolones are related to their variable structure, discover of new natural analogues to be therapeutically explored remains a significant framework of research. In this study, a new dithiolopyrrolone derivative was purified from the fermentation broth of S. algeriensis NRRL B-24137. This new antibiotic, characterized as benzoyl-pyrrothine dithiolopyrrolone, was induced by adding cinnamic acid, as precursor, to a semi-synthetic medium.

Isolation and Structure Elucidation of Cytotoxic Saccharothriolides D to F from a Rare Actinomycete Saccharothrix sp. and Their Structure-Activity Relationship

Three new 10-membered macrolides, saccharothriolides D-F (1-3), were isolated from a rare actinomycete, Saccharothrix sp. A1506. The planar structures were determined from analysis of extensive NMR and HR-ESI-MS data, and the absolute configurations were established by ECD spectroscopy analysis. Saccharothriolides D (1) and E (2) were determined to be C-2 epimers of saccharothriolides A (4) and B (5), respectively. Saccharothriolide F (3) was identified to be a demethylated congener of saccharothriolides D (1) and A (4) at the C-2 position. The availability of compounds 1-6 enabled a structure-activity relationship study that revealed the importance of the phenolic hydroxy group at C-2″ and the stereochemistry of C-2 for the inhibition of human fibrosarcoma HT1080 cell growth.

Streptosporangium becharense sp. nov., an actinobacterium isolated from desert soil

The taxonomic position of a novel actinobacterium, strain SG1^T, isolated from a Saharan soil sample collected from Béni-Abbès, Béchar (south-west Algeria), was established by using a polyphasic approach. The micro-organism had morphological and chemical features that were consistent with its classification in the genus Streptosporangium. The cell-wall peptidoglycan contained meso-diaminopimelic acid. The whole-cell sugars contained ribose and glucose, but not madurose. The predominant menaquinones were MK-9(H2) and MK-9(H4). The polar lipid profile contained diphosphatidylglycerol, phosphatidylmethylethanolamine, phosphatidylethanolamine, phosphatidylhydroxymethylethanolamine, phosphatidylhydroxyethanolamine, phosphatidylglycerol, phosphatidylinositol and phosphatidylinositol mannosides. The predominant cellular fatty acids were C17 : 1ω8c, iso-C16 : 0, 10-methyl C17 : 0, C18 : 1ω9c and C17 : 0. 16S rRNA gene sequence similarity analysis supported the classification of the isolate in the genus Streptosporangium and indicated that it was related most closely to 'Streptosporangium subfuscum' DSM 46724 (99.7 % similarity), Streptosporangium pseudovulgare DSM 43181^T (98.7 %), Streptosporangium fragile DSM 43847^T (98.6 %) and Streptosporangium sandarakinum DSM 45763^T (98.5 %). Phylogenetic analyses based on 16S rRNA gene sequences showed that strain SG1^T formed a cluster with its closest relative 'S. subfuscum' DSM 46724. However, DNA-DNA relatedness as well as physiological and chemotaxonomical analyses showed that strain SG1^T could be differentiated from its closest phylogenetic relatives. Therefore, it is proposed that strain SG1^T should be classified as representing a novel species in the genus Streptosporangium, for which the name Streptosporangiumbecharense sp. nov. is proposed. The type strain is SG1^T (=DSM 46887^T=CECT 8961^T).

Characterization and antagonistic properties of Streptomyces strains isolated from Saharan soils, and evaluation of their ability to control seedling blight of barley caused by Fusarium culmorum

During a screening for potential plant disease control actinomycetes, a total of 133 strains were isolated from Saharan soil samples of seven Algerian regions by dilution technique on chitin-vitamins agar medium. Screening for antagonistic properties using streak assay method showed that 25% of isolates demonstrated strong activities against a wide range of plant pathogenic fungi. Due to their strong anti-Fusarium activities, six of these isolates were selected and subsequently related to Streptomyces species by polyphasic analysis. These isolates were evaluated for their biocontrol ability against Fusarium culmorum, a serious pathogenic fungus of cereals crops related to damping-off and seedling blight resulting in yield loss. Barley seeds were chosen as cereal plant model. Surface bacterized seeds with TW3, RI3 and TW2 strains expressed the highest performances and permit to reduce significantly both the disease occurrence on seedlings (62-76%) and the extent of seedling blight symptoms (over than 95%). However, a negative effect on plant establishment was observed for RI3 treatment.

SIGNIFICANCE AND IMPACT OF THE STUDY

The genus Fusarium is considered to be one of the most problematic phytopathogenic fungi for crop culture worldwide. Inside this genus, F. culmorum is the aetiological agent of seedling blight in various monocotyledonous plants such as barley and cause extensive yield and quality losses in humid and semi-humid regions. Biological control may be a successful alternative to chemical control, particularly with the controversy surrounding the use of the fungicides and the limited obtained results to control F. culmorum. This study highlights the effectiveness of some antagonistic Streptomyces isolated from Algerian Saharan soils to control F. culmorum by the reduction in disease occurrence and disease severity suggesting their use on microbial biocontrol formulation against soilborne diseases.

The final acylation step in aromatic dithiolopyrrolone biosyntheses: identification and characterization of the first bacterium N-benzoyltransferase from Saccharothrix algeriensis NRRL B-24137

The last step in the biosynthesis of dithiolopyrrolone antibiotics was thought to involve the transfer of acyl group from acyl-CoA to pyrrothine/holothin core. In Saccharothrix algeriensis NRRL B-24137, two acyltransferases, an acetyltransferase and a benzoyltransferase were proposed to catalyze this step. We have previously identified, in Sa. algeriensis genome, two open read frames, actA and actB patiently encoded these enzymes. This study focuses primarily on the characterization of the protein encoded by actA. After cloning and expressing of actA in Escherichia coli BL21, the recombinant protein encoded by actA was purified. Selectivity of ActA for pyrrothine/holothin as substrate and different acyl-CoA as co-substrate was evaluated using two acyls-groups, linear and aromatic. The enzyme was shown to prefer aromatic groups over linear groups as donor group; further neither product nor transfer was observed for linear groups. Therefore ActA has been determined to be a pyrrothine/holothin N-benzoyltransferase which can either pyrrothine (Km of 72μM) or holothin (Km of 129.5μM) as substrates and benzoyl-CoA (Km of 348.65 and 395.28μM) as co-substrates for pyrrothine and holothin, respectively. The optimum pH and temperature has been shown to be 8, 40°C, respectively. ActA is the first enzyme characterized as N-benzoyltransferase in bacteria.

Identification of two putative acyltransferase genes potentially implicated in dithiolopyrrolone biosyntheses in Saccharothrix algeriensis NRRL B-24137

The dithiolopyrrolone class of antibiotics has been known to display bacteriostatic activity against both Gram-positive and Gram-negative bacteria and exert other biological activities. Acyltransferase activities are proposed to be responsible for the structural diversity of dithiolopyrrolones produced by Saccharothrix algeriensis NRRL B-24137. Moreover, two activities, pyrrothine N-acetyltransferase and pyrrothine N-benzoyltransferase, are reported to catalyze the formation, respectively, to thiolutin and benzoyl-pyrrothine (BEP) in this bacterium. In this study, two genes encoding two putative acyltransferases were identified in S. algeriensis. The first one, actA, was identified by bioinformatic analysis and by analogy to an acetyltransferase, hlmA, identified in holomycin biosynthetic gene cluster in Streptomyces clavuligerus. The second was identified by purification of both enzymes from the bacterial biomass which provided a semipurified extract. The microsequencing of tryptic peptides from the final protein preparation yielded sequences of eight different fragments, two of them encoded by one gene, actB, in S. algeriensis genome bank. The alignment of actB against the GenBank database revealed significant homology to acyltransferase family. Differential expression of these genes, actA and actB, was then investigated in three different media: (i) semisynthetic medium (SSM), which promotes the production of thiolutin; (ii) SSM supplemented by 1.25 mM benzoic acid (SSM + BA), which promotes the production of both thiolutin and BEP; and (iii) tryptic soy broth (TSB) in which no dithiolopyrrolone derivatives were detected.

Dithiolopyrrolone natural products: isolation, synthesis and biosynthesis

Dithiolopyrrolones are a class of antibiotics that possess the unique pyrrolinonodithiole (4H-[1,2] dithiolo [4,3-b] pyrrol-5-one) skeleton linked to two variable acyl groups. To date, there are approximately 30 naturally occurring dithiolopyrrolone compounds, including holomycin, thiolutin, and aureothricin, and more recently thiomarinols, a unique class of hybrid marine bacterial natural products containing a dithiolopyrrolone framework linked by an amide bridge with an 8-hydroxyoctanoyl chain linked to a monic acid. Generally, dithiolopyrrolone antibiotics have broad-spectrum antibacterial activity against various microorganisms, including Gram-positive and Gram-negative bacteria, and even parasites. Holomycin appeared to be active against rifamycin-resistant bacteria and also inhibit the growth of the clinical pathogen methicillin-resistant Staphylococcus aureus N315. Its mode of action is believed to inhibit RNA synthesis although the exact mechanism has yet to be established in vitro. A recent work demonstrated that the fish pathogen Yersinia ruckeri employs an RNA methyltransferase for self-resistance during the holomycin production. Moreover, some dithiolopyrrolone derivatives have demonstrated promising antitumor activities. The biosynthetic gene clusters of holomycin have recently been identified in S. clavuligerus and characterized biochemically and genetically. The biosynthetic gene cluster of thiomarinol was also identified from the marine bacterium Pseudoalteromonas sp. SANK 73390, which was uniquely encoded by two independent pathways for pseudomonic acid and pyrrothine in a novel plasmid. The aim of this review is to give an overview about the isolations, characterizations, synthesis, biosynthesis, bioactivities and mode of action of this unique family of dithiolopyrrolone natural products, focusing on the period from 1940s until now.

New alkaloid from Streptomyces koyangensis residing in Odontotermes formosanus

A new alkaloid was isolated from the ethyl acetate extract of the culture of a termite-associated Streptomyces koyangensis BY-4. The structure of 1 was elucidated by using MS, NMR, electronic circular dichroism data, and computational approaches. Compound 1 showed weak antimicrobial activities against a panel of test microbes.

New dithiolopyrrolone antibiotics induced by adding sorbic acid to the culture medium of Saccharothrix algeriensis NRRL B-24137

Dithiolopyrrolone antibiotics, produced by several microorganisms, are known for their strong antimicrobial activities. This class of antibiotics generated new interest after the discovery of their anticancer and antitumor properties. In this study, four new antibiotics were purified from the fermentation broth of Saccharothrix algeriensis NRRL B-24137 and characterized as dithiolopyrrolone derivatives. These new dithiolopyrrolone antibiotics were induced by adding sorbic acid, as precursor, at a concentration of 5 mM to the semi-synthetic medium. The analysis of the induced antibiotics was carried out by HPLC. The maximal production of the antibiotics PR2, PR8, PR9 and PR10 was 0.08±0.04, 0.21±0.04, 0.13±0.03 and 0.09±0.00 mg L(-1) , respectively, obtained after 8 days of fermentation. The chemical structures of these antibiotics were determined by (1) H- and (13) C-nuclear magnetic resonance, mass and UV-visible data. The four new dithiolopyrrolone antibiotics - PR2, PR8, PR9 and PR10 - were characterized, respectively, as crotonyl-pyrrothine, sorbyl-pyrrothine, 2-hexonyl-pyrrothine and 2-methyl-3-pentenyl-pyrrothine. The minimum inhibitory concentrations of the new induced antibiotics were determined.

New Acrylamide and Oxazolidin Derivatives from a Termite-Associated Streptomyces sp

Two new compounds, named 2-formylpyrrole-4-acrylamide (1) and dihydrostreptazolin (2) were isolated from the fermentation broth of BY-4, an actinomycetes residing in the gut of Odontotermes formosanus. The structures of 1 and 2 were elucidated by extensive spectral analysis (1H, 13C, 2D NMR, and HRESIMS). The isolated compounds were assayed for cytotoxic and antimicrobial activities.

Identification of the gene cluster for the dithiolopyrrolone antibiotic holomycin in Streptomyces clavuligerus

Streptomyces clavuligerus, an industrially important producer of clavulanate as well as cephem antibiotics, also produces the N-acylated dithiolopyrrolone antibiotic holomycin, a reported inhibitor of RNA synthesis. The genome sequence of S. clavuligerus ATCC 27064 was examined for a potential biosynthetic gene cluster, assuming that holomycin arises from some derivative of an L-Cys-L-Cys dipeptide that has undergone eight-electron oxidation, fused five-five ring formation, and decarboxylation. ORFs 3483-3492 comprise a candidate cluster, with a predicted acyltransferase, a stand-alone nonribosomal peptide synthetase (NRPS) module, and four flavin-dependent oxidoreductases. Deletions of ORF3488, the NRPS module, and ORF3489, a phosphopantothenoylcysteine decarboxylase homolog, abolished holomycin production both in wild type and in a holomycin-overproducing mutant. Heterologous expression and purification of ORF3488 allowed demonstration of L-Cys-AMP formation and subsequent covalent tethering of Cys to the phosphopantetheinyl arm of the thiolation domain of this NRPS protein. Purified ORF3483 shows acyltransferase activity, converting holothin to holomycin and longer acylated homologs as the last step in antibiotic assembly.