Search Results (182)

Marine-derived rare actinomycetes are a chemically prolific yet underexploited source of structurally diverse secondary metabolites. In this review, rare actinomycetes are operationally defined as marine-derived non-Streptomyces actinomycetes that remain comparatively underexplored yet possess demonstrated or predicted capacity for specialized-metabolite biosynthesis. Genome sequencing has revealed that their biosynthetic potential greatly exceeds the range of metabolites recovered under standard cultivation conditions. However, many reported compounds remain only loosely associated with the gene clusters that encode them. This review provides a biosynthesis-centered perspective on marine-derived rare actinomycetes, focusing on secondary metabolites for which biosynthetic gene clusters (BGCs) or pathways have been proposed, experimentally assessed, or functionally validated. It focuses on compounds reported after 2017, along with earlier metabolites whose biosynthetic origins were resolved only later. Representative examples are organized by genus and structural class and weighed according to the level of evidence linking each metabolite to its BGC, ranging from bioinformatic prediction and metabolomic correlation to validation by gene inactivation, heterologous expression, and enzymatic characterization. The surveyed metabolites include polyketides, nonribosomal peptides, polyketide synthase-nonribosomal peptide synthetase (PKS-NRPS) hybrids, siderophores, angucyclines, anthracyclines, macrolides, diketopiperazine derivatives, and other unusual scaffolds. Collectively, these findings indicate how integrating genome mining, metabolomics, and molecular networking with targeted biosynthetic experiments can accelerate marine natural product discovery and unravel novel enzymatic functions and biosynthetic mechanisms in rare actinomycetes. Full article

Rare actinomycetes have emerged as important yet underexplored reservoirs for the discovery of novel bioactive compounds. Microbispora, a genus of rare actinomycetes, is widely distributed across diverse ecological niches, including terrestrial soils, marine-associated environments, plant-associated ecosystems, and insect-derived environments. To date, 81 secondary metabolites have been reported from this genus, encompassing quinones, chromones and chromanones, macrolides, other polyketides, alkaloids, peptides and diketopiperazines, and miscellaneous structural classes. These metabolites display antimicrobial, anticancer, neuroprotective, antiviral, plant growth-promoting, and enzyme inhibitory activities. Beyond systematically cataloging these compounds, this review provides an integrated analysis of their structure–activity relationships (SAR), biosynthetic origins, and biological significance. In addition, the biosynthetic potential of Microbispora is discussed based on reported genomic studies, highlighting the presence of numerous predicted and poorly characterized biosynthetic gene clusters. This review provides an integrative perspective on Microbispora as an underexplored but promising source of structurally diverse and bioactive natural products for drug discovery. Full article

Runting and stunting syndrome (RSS) has been reported worldwide in commercial aquaculture and is frequently observed in juvenile-rearing ponds of Apostichopus japonicus. The objective of this study was to use commercially cultured A. japonicus naturally affected by RSS under high-density culture conditions as the study subjects. Different nutritional additive treatments, including marine mud, effective microorganisms (EM; photosynthetic bacteria, lactic acid bacteria, yeasts, and actinomycetes), yeast, kelp powder, and fermented kelp powder, were applied, and growth performance during recovery, the activities of intestinal digestive enzymes (protease, alginate lyase and cellulase), and heterotrophic bacterial counts were systematically evaluated. The results showed that the recovery rate of RSS in A. japonicus decreased in the following order: the EM group (90.91 ± 1.15%), the fermented kelp group (90.91 ± 4.96%), the yeast group (81.82 ± 5.99%), the kelp group (72.73 ± 1.35%), the marine mud group (63.64 ± 1.41%), and the control group (54.55 ± 1.47%). Moreover, increased intestinal digestive enzyme activities, elevated heterotrophic bacterial counts, and a reduced relative abundance of Vibrio were identified as key factors associated with RSS recovery in A. japonicus, with the EM and fermented kelp groups showing the most pronounced effects. High-throughput sequencing further revealed that nutritional additive treatments differed in their effects on the intestinal microbial community structure of RSS-affected A. japonicus. At the phylum level, Bacillota (26.45–48.08%), Actinomycetota (13.96–44.99%), and Pseudomonadota (9.15–56.46%) were the dominant phyla in the intestine of A. japonicus. At the genus level, a lower relative abundance of Vibrio was associated with improved recovery, and groups with lower Vibrio levels generally exhibited better recovery outcomes; notably, the EM group showed the lowest relative abundance of Vibrio (1.37%). Overall, these community shifts may contribute to recovery by supporting potential energy supply, immune regulation, and functional restoration. Therefore, these findings provide new insights into the treatment of RSS in A. japonicus through the development of beneficial microbes and the targeted suppression of potential pathogens. Full article

This study explores the taxonomic diversity, metabolic profile, and bioactivity of marine-derived actinomycetes isolated from sediments collected off the coast of Lisbon and Setúbal Peninsula, Portugal. The combined use of two sediment pre-treatments (heat shock and dry overnight) and four growth media with varying nutrient concentrations revealed that formulations 10% A1 and SWA were most effective for recovering diverse actinomycetes, including rare Actinomadura, resulting in a total of 142 cultivable strains closely related to 47 phylogenetic distinct species dominated by Streptomyces and Micromonospora. Antimicrobial screening against methicillin-resistant Staphylococcus aureus (MRSA, COL) and Escherichia coli (K12) identified 22 bioactive strains, with strain PTS-083 exhibiting the strongest activity against MRSA (MIC = 1.95 µg/mL) and a 98.30% 16S rRNA gene identity to S. chumphonensis, highlighting it as a strong candidate for further metabolite and genomic studies. Cytotoxicity assays against HCT-116 human colorectal adenocarcinoma cells revealed eight bioactive strains with potent anticancer activity for extracts from strains related to S. sundarbansensis, S. violaceorubidus, and S. aculeolatus (IC₅₀ < 0.005–5.08 µg/mL). Untargeted LC-MS/MS metabolomic analysis uncovered a wide array of secondary metabolites, including macrolides, siderophores, fatty acids, and cyclic peptides. Comparative analyses with other Portuguese coastal studies revealed both shared and distinctive metabolomic profiles, emphasizing the importance of exhaustive sampling, even at nearby locations, since localized environmental conditions can influence metabolic diversity and are crucial for uncovering unique metabolites with potential biotechnological value. These findings highlight Portugal’s coastal sediments as a rich and underexplored source of novel actinomycetes and bioactive compounds with promising pharmaceutical applications. Full article

Soils with an albic horizon (characterized by a bleached, nutrient-poor eluvial layer), classified primarily as Albic Planosols and associated groups (e.g., Albic Luvisols and Retisols) in the World Reference Base for Soil Resources (WRB), are widespread in Northeast China and suffer from inherent poor nutrient availability and low crop productivity. The present study aimed to evaluate the efficacy of novel microbial–enzyme composite biofertilizers in ameliorating Albic soils. This comprehensive assessment investigated their effects on soil nutrient availability, microbial community structure, and the activities of key enzymes involved in nutrient cycling (e.g., dehydrogenase and phosphatase). Concurrently, the impact on maize crop performance was determined by measuring changes in agronomic traits, including chlorophyll content, stem diameter, and final grain yield. A field experiment was conducted in Heilongjiang Province during the 2023 maize growing season using a randomized block design with six treatments: CF (conventional chemical fertilizer, 330 kg·ha⁻¹ NPK), OF (chemical fertilizer + 1500 kg·ha⁻¹ organic carrier), BF1 (OF + 75 kg·ha⁻¹ marine actinomycetes), BF2 (OF + 75 kg·ha⁻¹ actinomycetes + 45 kg·ha⁻¹ phytase), BF3 (OF + 75 kg·ha⁻¹ actinomycetes + 45 kg·ha⁻¹ mycorrhizal fungi + 45 kg·ha⁻¹ phytase), and BF4 (OF + 75 kg·ha⁻¹ actinomycetes + 45 kg·ha⁻¹ mycorrhizal fungi + 45 kg·ha⁻¹ phytase + 45 kg·ha⁻¹ β–glucosidase). The results showed that biofertilizers significantly increased microbial abundance and enzyme activity. The integrated treatment BF4 notably enhanced topsoil fungal abundance by 188.1% and dehydrogenase activity in the 0–20 cm layer, while also increasing available phosphorus by 92.6% at maturity. Although BF4 improved soil properties the most, BF3 produced the highest maize yield—boosting grain output by 18.3% over CF—and improved stem diameter and chlorophyll content. Strong correlations between microbial parameters and enzyme activities indicated a nutrient-cycling mechanism driven by microorganisms, with topsoil fungal abundance positively linked to alkaline phosphatase activity (r = 0.72) and subsoil bacterial abundance associated with available phosphorus (r = 0.65), demonstrating microbial–mediated carbon–phosphorus coupling. In conclusion, microbial–enzyme biofertilizers, particularly BF4, provide a sustainable strategy for enhancing Albic soil fertility and crop productivity. Full article

Mangrove forests represent a complex ecosystem inhabiting tropical and subtropical intertidal zones, harboring diverse microbial communities including fungi, actinomycetes, bacteria, cyanobacteria, algae, and protozoa. Among these communities, mangrove-derived fungi, as the second-largest ecological group of marine fungi, not only play essential roles in establishing and sustaining this biosphere but also serve as an important source of structurally unique and biologically active secondary metabolites. This review systematically summarizes research progress on metabolites isolated from mangrove-derived fungi and their associated bioactivities over the recent five years (2020–2025). Emphasis is placed on 457 metabolites documented in 97 selected publications, with a focus on the biological activities and distinctive chemical diversity of these secondary metabolites. This review provides an important reference for the research status of secondary metabolites isolated from mangrove-derived fungi and the lead compounds worthy of further development, and reveals that mangrove-derived fungi have important medicinal values and are worthy of further development. Full article

In this study, we report the isolation of the known compound 6-isoprenylindole-3-carboxylic acid (SJ196), a prenylated indole derivative, from a marine Streptomyces sp., APA053, and its potent anti-melanogenic activity. SJ196 showed ABTS and DPPH radical scavenging activities and cellular antioxidant activities, significantly suppressing cytoplasmic and mitochondrial reactive oxygen species (ROS) in B16F10 murine melanoma cells. Furthermore, SJ196 reduced both intracellular and extracellular melanin content without cytotoxicity. These effects coincided with suppression of intracellular signal transduction for melanogenesis, significantly reducing phosphorylation of ERK, JNK, and p38 MAPK, and attenuating the expression of MITF and melanogenic enzymes (TYR, TRP-1, and TRP-2). Importantly, in a three-dimensional human skin model (MelanoDerm™), SJ196 exhibited a skin-lightening effect, as evidenced by dose-dependent increases in skin brightness and histological confirmation. Collectively, we demonstrated that SJ196 is a potent anti-melanogenic marine compound that acts through antioxidant activity and MAPK-MITF pathway suppression, suggesting its therapeutic potential for the treatment of age-related hyperpigmentation disorders. Full article

Marine actinomycetes constitute a vigorous source of bioactive compounds with potential anti-tumor activity. This study investigates the antitumor activity and classification of actinomycetes isolated from 32 marine soil samples collected across four seasons from Tyr City Beach, Lebanon. A total of 80 morphologically diverse isolates were recovered and characterized, with dominant genera including Streptomyces, Kocuria, and Micrococcus. Among these, three promising strains—Kocuria rosea, Micrococcus luteus, and Streptomyces longisporoflavus—were selected for further analysis. Crude extracts were tested against human colorectal adenocarcinoma (Caco-2) and human hepatocellular carcinoma (HepG-2) cancer cell lines using MTT and Western blot assays. At the highest concentration (8 µg/µL), the extracts reduced cell viability to 24–37% in Caco-2 and 12–25% in HepG-2. The IC₅₀ values ranged from 1.72 to 3.53 µg/µL, depending on the extract and cell line. Western blot analysis showed dose-dependent increases in the Bax/Bcl-2 ratio, with fold changes reaching 4.35 (Kocuria), 11.39 (Micrococcus), and 14.25 (Streptomyces) in HepG-2 cells. The p53 protein expression also increased significantly, with fold changes up to 7.79 in Caco-2 and 3.0 in HepG-2 cells. These results indicate that marine actinomycetes from the Lebanese coastline hold strong potential as a source of antitumor agents targeting apoptosis pathways. Full article

Marine-derived Actinomycetota have emerged as promising sources of bioactive natural products, particularly filamentous actinomycetes (e.g., Streptomyces). However, members from non-filamentous genera have showed potential biotechnological importance. In this study, we performed a comprehensive genomic characterization of two bioactive Brevibacterium strains, Brevibacterium luteolum (B. luteolum) 26C and Brevibacterium casei (B. casei) 13A, isolated from two Red Sea sponges. Whole-genome sequencing and taxonomic analysis confirmed species-level identification, marking the first documented report of these species within the Red Sea ecosystem. The two strains displayed antimicrobial activity against Staphylococcus aureus, Escherichia coli, and Candida albicans. Additionally, functional annotation revealed multiple genomic islands (GIs) enriched with genes conferring heavy metal resistance, DNA repair enzymes, nutrient acquisition, and mobile genetic elements, highlighting potential evolutionary adaptations to the harsh physicochemical conditions of the Red Sea. Genome mining identified biosynthetic gene clusters, including those encoding ε-poly-L-lysine, tropodithietic acid, ectoine, and carotenoids. The comparative analysis of orthologous gene clusters from both strains and their counterparts from terrestrial ecosystems highlighted potential marine adaptive genetic mechanisms. This study highlights the biosynthetic potential of B. luteolum 26C and B. casei 13A and their ecological role as active competitors and potential defensive associates within the sponge microbiome. Full article

Humic substances and beneficial microorganisms are key biostimulants for sustainable agriculture and global food security in the face of climate change. Marine bacteria are emerging as a promising source of plant-beneficial microbes, tapping into a microbial diversity as immense as the oceans themselves. However, their potential, limitations, and mechanisms of action––especially in combination with other biostimulants––remain largely unexplored. In this study, we isolated the Streptomyces sp. LAP3 strain from the giant limpet Scutellastra mexicana. We evaluated the efficacy of the marine bacterium, applied alone or in combination with the humic product Leonardite hydrolate (L), in enhancing tomato performance under field conditions. Treatments included: (1) marine Streptomyces (MS), (2) Leonardite hydrolate (L), (3) both biostimulants (MS + L), and (4) a control (CTRL). We assessed growth, photosynthetic performance, antioxidant responses, and fruit yield and quality. Both biostimulants individually improved plant performance, but their combination had a significant synergistic effect, markedly boosting tomato productivity, thermotolerance, and resilience during a heatwave. Enhanced photosynthetic efficiency and antioxidant enzyme activity were associated with improved agronomic traits. These results highlight the potential of combining Streptomyces sp. LAP3 and Leonardite hydrolate as an eco-friendly strategy to increase crop productivity, strengthen stress resilience, promote sustainable agriculture, and reduce reliance on agrochemicals. Full article

Pseudopeptides are attractive agents for protease inhibition due to their structural similarities to the natural substrates of these enzymes, as well as their enhanced stability and resistance to enzymatic degradation. We report three new ketomemicin pseudopeptides (1–3) from extracts of the marine actinomycete Salinispora pacifica strain CNY-498. Their constitution and relative configuration were elucidated using NMR, mass spectrometry, and quantum chemical calculations. Using GNPS molecular networking and publicly available Salinispora LCMS datasets, five additional ketomemicin analogs (4–8) were identified with ketomemicin production detected broadly across Salinispora species. The ketomemicin biosynthetic gene cluster (ktm) is highly conserved in Salinispora, occurring in 79 of 118 public genome sequences, including eight of the nine named species. Outside Salinispora, ktm homologs were detected in various genera of the phylum Actinomycetota that might encode novel ketomemicin analogs. Ketomemicins 1–3 were tested against a panel of eleven proteases, with 2 displaying moderate inhibitory activity. This study describes the first report of ketomemicin production by Salinispora cultures, the distribution of the corresponding biosynthetic gene cluster, and the protease inhibitory activity of new ketomemicin derivatives. Full article

The development of extensive antibiotic resistance has created an urgent demand to identify novel sources of antimicrobial agents. Interest in actinomycetes has become prevalent around the world because of their ability to generate several beneficial bioactive metabolites. In the present study, 32 marine soil samples were collected from Tyre City Beach, Lebanon, in different seasons. A total of 10 actinomycetes species were identified and characterized depending on their microscopic features. All isolates were tested for their potential to exert antimicrobial activities against varied microorganisms using cross-streak and agar well diffusion methods. All isolates displayed significant antimicrobial activities against the tested indicator microorganisms. Similarly, all 10 isolates of marine actinomycetes exhibited antifungal activity in cross-streak tests against Candida albicans, Aspergillus niger, and Aspergillus flavus. Moreover, the optimum conditions used to enhance the production of antimicrobial secondary metabolites against Bacillus cereus were tested for the three isolates Kocuria rosea, Micrococcus luteus, and Streptomyces longisporoflavus. Our results indicate that actinomycetes isolated from Tyre City Beach, Lebanon, represent a promising source of antimicrobial bioactive substances. Full article

Four new kaurane-type diterpenoids, geliboluols A–D (1–4), along with one known analog (5), were isolated from the culture broth of the marine-derived rare actinomycete Actinomadura geliboluensis. The structures of compounds 1–4 were determined by spectroscopic analysis (HR-ESIMS, 1D, and 2D NMR), the MPA method, and by comparing their optical rotation values with those in the literature. The new compounds were evaluated for their cytotoxicity against seven blood cancer cell lines by a CellTiter-Glo (CTG) assay and six solid cancer cell lines by a sulforhodamine B (SRB) assay. Among the new compounds, compound 4 exhibited moderate cytotoxic activity against some blood cancer cell lines, with GI₅₀ values ranging from 2.59 to 19.64 µM, and against solid cancer cell lines with GI₅₀ values ranging from 4.34 to 7.23 µM. Full article

This study investigated the fatty acids (FA) profile of 54 actinomycete strains isolated from marine sediments collected off the Portugal continental coast, specifically from the Estremadura Spur pockmarks field, by GC/MS. Fatty acid methyl esters (FAMEs) were prepared from the ethyl acetate lipidic extracts of these strains and analyzed by gas chromatography–mass spectrometry (GC/MS), with FA identification performed using the NIST library. The identified FAs varied from C12:0 to C20:0, where 32 distinct FAs were identified, including 7 branched-chain fatty acids (BCFAs), 9 odd-chain fatty acids (OCFAs), 8 monounsaturated fatty acids (MUFAs), 6 saturated fatty acids (SFAs), 1 polyunsaturated fatty acid (PUFA), and 1 cyclic chain fatty acid (CCFA). The average expressed content was BCFA (47.54%), MUFA (28.49%), OCFA (26.93%), and SFA (22.16%), of which i-C16:0, C18:1ω9, and C16:0 were predominant, while PUFA (3.58%) and CCFA (0.41%) were identified as minor components. The identified BCFA were i-C16:0, a-C15:0, i-C15:0, i-C15:1ω6, a-C16:0, a-C14:0, and i-C17:0, which include combined branching and unsaturation and branching and odd. SFAs were present in all species, with C16:0 and C18:0 being the most representative. Rare OCFAs C19:1ω9, C17:1ω7, C15:0, and C17:0 were expressed. PUFA C18:1ω9 was detected; within this class, omega families ω9, ω7, ω6, and ω5 were identified, and no ω3 was detected. The only CCFA was benzene-butanoic acid (benzene-C4:0). These findings highlight the metabolic versatility of actinomycetes, providing valuable insights into microbial chemotaxonomy and offering promising biochemical leads for the development of biofuel, nutraceutical, and antifungal agents. Furthermore, these results underline the diversity and biotechnological potential of FAs in actinomycetes, uncovering their potential to be used as microbial cell factories, and paving the way for innovations in biofuels, pharmaceuticals, and eco-friendly industrial products. Full article

The increase in cancer incidence in recent years necessitates urgent exploration of novel and alternative sources of natural bioactives for targeted cancer therapy. Approximately 75% of the Earth’s surface is covered by oceans, which are thought to harbor untapped physiologically active compounds with potential efficacy against cancer. Recently, a growing focus has been on isolating and investigating novel bioactive compounds derived from marine sources. Bioactive metabolites with diverse chemical structures, isolated from various marine species such as algae, mollusks, and actinomycetes, demonstrate potential efficacy against a wide range of cancers. To our knowledge, this is one of the articles that has reviewed recent papers on the application of marine-derived bioactives in targeted cancer therapy. This study aims to showcase some of the most current developments in targeted cancer therapy with various bioactives that have been identified from marine sources. Full article