Structurally diverse metabolites from the rare actinobacterium Saccharothrix xinjiangensis

Discovering the secondary metabolic potential of Saccharothrix

Rare actinomycetes are highly valued as potential sources of novel bioactive secondary metabolites. Among these rare actinomycetes, the genus Saccharothrix is particularly noteworthy due to its ability to produce a diverse range of bioactive secondary metabolites. With the continuous sequencing of bacterial genomes and the rapid development of bioinformatics technologies, our knowledge of the secondary metabolic potential of Saccharothrix can become more comprehensive, but this space has not been reviewed or explored. This review presents a detailed overview of the chemical structures and bioactivities of 138 Saccharothrix-derived secondary metabolites, which are classified into five distinct groups based on their biosynthetic pathways. Furthermore, we delve into experimentally characterized biosynthetic pathways of nine bioactive metabolites. By utilizing a combination of cheminformatic and bioinformatic approaches, we attempted to establish connections between the metabolite families and the biosynthetic gene cluster families encoded by Saccharothrix strains. Our analysis provides a comprehensive perspective on the secondary metabolites that can be linked to corresponding BGCs and highlights the underexplored biosynthetic potential of Saccharothrix. This review also provides guidance for the targeted discovery and biosynthesis of novel natural products from Saccharothrix.

Marine natural products

Covering: 2020This review covers the literature published in 2020 for marine natural products (MNPs), with 757 citations (747 for the period January to December 2020) referring to compounds isolated from marine microorganisms and phytoplankton, green, brown and red algae, sponges, cnidarians, bryozoans, molluscs, tunicates, echinoderms, mangroves and other intertidal plants and microorganisms. The emphasis is on new compounds (1407 in 420 papers for 2020), together with the relevant biological activities, source organisms and country of origin. Pertinent reviews, biosynthetic studies, first syntheses, and syntheses that led to the revision of structures or stereochemistries, have been included. A meta analysis of bioactivity data relating to new MNPs reported over the last five years is also presented.

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.

Natural Polypropionates in 1999-2020: An Overview of Chemical and Biological Diversity

Natural polypropionates (PPs) are a large subgroup of polyketides with diverse structural features and bioactivities. Most of the PPs are discovered from marine organisms including mollusks, fungi and actinomycetes, while some of them are also isolated from terrestrial resources. An increasing number of studies about PPs have been carried out in the past two decades and an updated review is needed. In this current review, we summarize the chemical structures and biological activities of 164 natural PPs reported in 67 research papers from 1999 to 2020. The isolation, structural features and bioactivities of these PPs are discussed in detail. The chemical diversity, bioactive diversity, biodiversity and the relationship between chemical classes and the bioactivities are also concluded.

Nonocarbolines A-E, β-Carboline Antibiotics Produced by the Rare Actinobacterium Nonomuraea sp. from Indonesia

During the course of our ongoing screening for novel biologically active secondary metabolites, the rare Actinobacterium, Nonomuraea sp. 1808210CR was found to produce five unprecedented β-carboline derivatives, nonocarbolines A-E (1-5). Their structures were elucidated from high-resolution mass spectrometry, 1D and 2D nuclear magnetic resonance spectroscopy, and the absolute configuration of 4 was determined by using the modified Mosher method. Nonocarboline B (2) displayed moderate antifungal activity against Mucor hiemalis, while nonocarboline D (4) exhibited significant cytotoxic activity against the human lung carcinoma cell line A-549 with the IC50 value of 1.7 µM.