Genomic insight into a novel actinobacterium, Actinomadura rubrisoli sp. nov., reveals high potential for bioactive metabolites

A Catch-Release Strategy for the Genomics-Driven Discovery of Antiproliferative Furan-Functionalized Peptides

Furan-functionalized peptides are of significant pharmacological interest due to their pronounced bioactivities and unique potential for orthogonal bioconjugation and derivatization. However, naturally occurring peptides with furyl side chains are exceedingly rare. This study presents a streamlined method to predict and assess the microbial production of peptides incorporating 3-furylalanine (Fua) moieties. The approach integrates genome mining and the reversible, chemoselective tagging of furyl residues, utilizing their unique Diels-Alder reactivity, for mass-spectrometry-guided identification of candidate compounds. By employing the rhizonin Fua synthase as a bioinformatic handle and through heterologous reconstitution of Fua biosynthesis, we identified previously unknown Fua biosynthetic pathways in diverse bacterial phyla, including actinomycetes, cyanobacteria, actinobacteria, and γ-proteobacteria, suggesting that Fua-containing peptides are remarkably widely distributed. Metabolic profiling by reversible tagging facilitated the detection of Fua-containing metabolites in their native producers. The successful adaptation of this method for solid support enabled the direct enrichment of furyl-substituted peptides from complex mixtures. This multi-pronged approach enabled the discovery and characterization of two novel families of Fua cyclopeptides (rubriamides and typhamides) with potent antiproliferative effects against human tumor cells and nematodes. The innovative catch-and-release strategy, in conjunction with genome mining, represents a valuable tool for the discovery of new furan-substituted natural products.

Actinomadura monticuli sp. nov., isolated from Darangshi Oreum (a volcanic cone), and the reclassification of Actinomadura glauciflava Lu et al. 2003 as a later heterotypic synonym of Actinomadura luteofluorescens (Shinobu 1962) Preobrazhenskaya et al. 1975 (Approved Lists 1980)

Two mycelium-forming actinobacterial strains, designated as DLS-47 and DLS-62T, were isolated from volcanic ash collected from the surface of a rock on the peak of Darangshi Oreum (a volcanic cone) in Jeju, Republic of Korea, and their taxonomic positions were investigated by a polyphasic approach. Both of the isolates showed growth at 20-42 °C, pH 6.0-9.0 and 0-1% (w/v) NaCl. Furthermore, DLS-47 was found to grow at 45 °C, while strain DLS-62T grew at pH 10.0 and 3% (w/v) NaCl. The 16S rRNA gene-based phylogeny showed that both of the isolates belonged to the genus Actinomadura; strain DLS-47 was most closely related to Actinomadura chokoriensis DSM 45346T (100% sequence identity), while strain DLS-62T formed a tight cluster with Actinomadura bangladeshensis DSM 45347T (99.5% sequence similarity). Morphological and chemotaxonomic characteristics supported the affiliation of the two isolates to the genus Actinomadura. Phylogenomic analysis based on 92 core gene sequences showed that both of the isolates were most closely related to A. chokoriensis DSM 45346T. Strain DLS-47 shared 100% of orthologous average nucleotide identity and digital DNA-DNA hybridization values with A. chokoriensis DSM 45346T, while strain DLS-62T showed orthologous average nucleotide identity ≤89.8% and digital DNA-DNA hybridization values ≤39.4% with strain DLS-47 and members of the genus Actinomadura. The results of phenotypic assays and comparison of overall genomic relatedness indices support the conclusion that strain DLS-47 (= KACC 23347=DSM 116423) is a strain of A. chokoriensis, while strain DLS-62T (= KACC 23345T = DSM 116424T) represents a new species of the genus Actinomadura, for which the name Actinomadura monticuli sp. nov. is proposed. Also, Actinomadura glauciflava Lu et al. 2003 is reclassified as a later heterotypic synonym of Actinomadura luteofluorescens (Shinobu 1962) Preobrazhenskaya et al. 1975 (Approved Lists 1980) based on analysis of overall genomic relatedness indices and phenotypic similarity.

Actinomadura terrae sp. nov. and Actinomadura litoris OS3-89, isolated from rhizosphere soil of cactus

Two mycelium-forming actinobacterial strains, designated OS3-83 ^T and OS3-89, were isolated from rhizosphere soil of a cactus (Opuntia ficus-indica) sampled on Mara Island, Jeju, Republic of Korea. Both of the isolates were found to grow at 20-37 °C, pH 6.0-10.0 and with 0-2 % (w/v) NaCl. Their taxonomic positions were investigated by a polyphasic approach. Strains OS3-83^T and OS3-89 were most closely related to the type strain of Actinomadura litoris (99.5 % and 98.9 % 16S rRNA gene sequence similarity, respectively). Both of the isolates shared 99.2 % sequence similarity to each other. Morphological and chemotaxonomic characteristics supported the affiliation of the two isolates to the genus Actinomadura. 16S rRNA gene phylogeny exhibited that strain OS3-83^T formed a tight cluster with A. litoris, while strain OS3-89 occupied a position located remotely from A. litoris. Nevertheless, phylogenomic analysis based on 92 core gene sequences showed that both of the isolates formed a tight clade with A. litoris. The values of average nucleotide identity and digital DNA-DNA hybridization between strain OS3-83^T and the closest relative, A. litoris, were 92.2 and 46.2 %, respectively, whereas strain OS3-89 shared an average nucleotide identity value of 97.5 % and a digital DNA-DNA hybridization value of 76.9 % with A. litoris. These results strongly suggested that strain OS3-83^T (=KACC 19752^T=NBRC 114688^T) represents a novel species and strain OS3-89 (=KACC 19753=NBRC 114400) is a strain of A. litoris. On the basis of the data obtained here, strain OS3-83^T is considered to represent a new species of the genus Actinomadura, for which the name Actinomadura terrae sp. nov. is proposed.

Actinomadura soli sp. nov., isolated from the top soil layer on basaltic material in Turkey

An actinobacterium, designated 14C53^T, was isolated from a soil sample on basaltic material from Samsun, Turkey. The growth ranges for NaCl concentration and pH of strain 14C53^T were quite limited and the growth temperature range of the strain was 20-37 °C, with an optimum at 28 °C. Phylogenetic analysis of 16S rRNA gene sequences revealed that strain 14C53^T was most closely related to Actinomadura geliboluensis A8036^T (98.5 % similarity value), but in the phylogenetic tree, it formed a clade with Actinomadura alkaliterrae D310A^T. The genome tree revealed a close relationship between the strain and Actinomadura pelletieri DSM 43383^T. However, the digital DNA-DNA hybridization and average nucleotide identity values between strain 14C53^T with Actinomadura geliboluensis A8036^T and Actinomadura pelletieri DSM 43383^T were 28.6-30.2 % and 84.3-85.5 %, respectively, and comparative analyses based on the genome sequences demonstrated that it represents a novel species of the genus Actinomadura. The genome size of strain 14C53^T was approximately 9.0 Mb and the genomic DNA G+C content of the strain was 71.3 mol%. The major cellular fatty acids of strain 14C53^T were C_16 : 0 and iso-C_16 : 0. Strain 14C53^T contained meso-diaminopimelic acid as the diamino acid in the cell-wall peptidoglycan. The predominant menaquinones were MK-9(H₈) and MK-9(H₆). Based on evidence collected from the phenotypic, genotypic and phylogenetic analyses, a novel species Actinomadura soli sp. nov. is proposed, with 14C53^T (=DSM 104447^T=KCTC 39878^T) as the type strain.