Lunaemycins, New Cyclic Hexapeptide Antibiotics from the Cave Moonmilk-Dweller MM109.

strains have been isolated from moonmilk deposits, which are calcium carbonate speleothems used for centuries in traditional medicine for their antimicrobial properties. Genome mining revealed that these strains are a remarkable example of a species with huge heterogeneity regarding their content in biosynthetic gene clusters (BGCs) for specialized metabolite production. BGC 28a is one of the cryptic BGCs that is only carried by a subgroup of .

Structure of New Ferroverdins Recruiting Unconventional Ferrous Iron Chelating Agents.

Ferroverdins are ferrous iron (Fe)-nitrosophenolato complexes produced by a few species as a response to iron overload. Previously, three ferroverdins were identified: ferroverdin A, in which three molecules of -vinylphenyl-3-nitroso-4-hydroxybenzoate (-vinylphenyl-3,4-NHBA) are recruited to bind Fe, and Ferroverdin B and Ferroverdin C, in which one molecule of -vinylphenyl-3,4-NHBA is substituted by hydroxy--vinylphenyl-3,4-NHBA, and by carboxy--vinylphenyl-3,4-NHBA, respectively. These molecules, especially ferroverdin B, are potent inhibitors of the human cholesteryl ester transfer protein (CETP) and therefore candidate hits for the development of drugs that increase the serum concentration of high-density lipoprotein cholesterol, thereby diminishing the risk of atherosclerotic cardiovascular disease.

On the Risks of Phylogeny-Based Strain Prioritization for Drug Discovery: as a Case Study.

Strain prioritization for drug discovery aims at excluding redundant strains of a collection in order to limit the repetitive identification of the same molecules. In this work, we wanted to estimate what can be unexploited in terms of the amount, diversity, and novelty of compounds if the search is focused on only one single representative strain of a species, taking as a model. For this purpose, we selected 18 strains taxonomically clustered with the archetype strain MM109.

A Single Biosynthetic Gene Cluster Is Responsible for the Production of Bagremycin Antibiotics and Ferroverdin Iron Chelators.

Biosynthetic gene clusters (BGCs) are organized groups of genes involved in the production of specialized metabolites. Typically, one BGC is responsible for the production of one or several similar compounds with bioactivities that usually only vary in terms of strength and/or specificity. Here we show that the previously described ferroverdins and bagremycins, which are families of metabolites with different bioactivities, are produced from the same BGC, whereby the fate of the biosynthetic pathway depends on iron availability.

Complete Genome Sequence of Streptomyces lunaelactis MM109, Isolated from Cave Moonmilk Deposits.

MM109 is a ferroverdin A (anticholesterol) producer isolated from cave moonmilk deposits. The complete genome sequence of MM109 was obtained by combining Oxford Nanopore MinION and Illumina HiSeq and MiSeq technologies, revealing an 8.4-Mb linear chromosome and two plasmids, pSLUN1 (127,264 bp, linear) and pSLUN2 (46,827 bp, circular).

Isolation, Characterization, and Antibacterial Activity of Hard-to-Culture Actinobacteria from Cave Moonmilk Deposits.

Cave moonmilk deposits host an abundant and diverse actinobacterial population that has a great potential for producing novel natural bioactive compounds. In our previous attempt to isolate culturable moonmilk-dwelling Actinobacteria, only species were recovered, whereas a metagenetic study of the same deposits revealed a complex actinobacterial community including 46 actinobacterial genera in addition to streptomycetes. In this work, we applied the rehydration-centrifugation method to lessen the occurrence of filamentous species and tested a series of strategies to achieve the isolation of hard-to-culture and rare Actinobacteria from the moonmilk deposits of the cave "Grotte des Collemboles".

Contribution of the β-glucosidase BglC to the onset of the pathogenic lifestyle of Streptomyces scabies.

Common scab disease on root and tuber plants is caused by Streptomyces scabies and related species which use the cellulose synthase inhibitor thaxtomin A as the main phytotoxin. Thaxtomin production is primarily triggered by the import of cello-oligosaccharides. Once inside the cell, the fate of the cello-oligosaccharides is dichotomized: (i) the fuelling of glycolysis with glucose for the saprophytic lifestyle through the action of β-glucosidase(s) (BGs); and (ii) elicitation of the pathogenic lifestyle by the inhibition of CebR-mediated transcriptional repression of thaxtomin biosynthetic genes.

Assessment of the Potential Role of in Cave Moonmilk Formation.

Moonmilk is a karstic speleothem mainly composed of fine calcium carbonate crystals (CaCO) with different textures ranging from pasty to hard, in which the contribution of biotic rock-building processes is presumed to involve indigenous microorganisms. The real microbial input in the genesis of moonmilk is difficult to assess leading to controversial hypotheses explaining the origins and the mechanisms (biotic vs. abiotic) involved.

A Phenotypic and Genotypic Analysis of the Antimicrobial Potential of Cultivable Isolated from Cave Moonmilk Deposits.

Moonmilk speleothems of limestone caves host a rich microbiome, among which Actinobacteria represent one of the most abundant phyla. Ancient medical texts reported that moonmilk had therapeutical properties, thereby suggesting that its filamentous endemic actinobacterial population might be a source of natural products useful in human treatment. In this work, a screening approach was undertaken in order to isolate cultivable Actinobacteria from moonmilk of the Grotte des Collemboles in Belgium, to evaluate their taxonomic profile, and to assess their potential in biosynthesis of antimicrobials.

Growth of desferrioxamine-deficient Streptomyces mutants through xenosiderophore piracy of airborne fungal contaminations.

Due to the necessity of iron for housekeeping functions, nutrition, morphogenesis and secondary metabolite production, siderophore piracy could be a key strategy in soil and substrate colonization by microorganisms. Here we report that mutants of bacterium Streptomyces coelicolor unable to produce desferrioxamine siderophores could recover growth when the plates were contaminated by indoor air spores of a Penicillium species and Engyodontium album. UPLC-ESI-MS analysis revealed that the HPLC fractions with the extracellular 'resuscitation' factors of the Penicillium isolate were only those that contained siderophores, i.