Marine Actinomycetes Research Articles

Bioactive secondary metabolites from marine actinomycetes and their inhibitory effect on bacteria of Drinking water

Bioactive secondary metabolites from marine actinomycetes and their inhibitory effect on bacteria of Drinking water

Isolation, Identification and Screening of Potential Marine Actinomycete for Lipase Production under Submerged Fermentation by using Tributyrin substrate

Ninety-six isolates were collected at various depths and sea shores of the Bay of Bengal near Visakhapatnam Coastal of Andhra Pradesh. These isolates were screened for the isolation of lipase activity by tributyrin agar clearing method and cultured under submerged fermentation and assayed for extra cellular lipase production by using tributyrin as substrate. Cultural characteristics of the selected strain was done by incorporating different media. Various parameters namely morphological, biochemical, physiological and molecular were used for the characterization and identification of actinomycetes isolates. Results indicated that all the isolates showed lipolytic activity after primary screening. The marine isolate T9 was the most active one thus the same was selected for production of lipase. The 16S rDNA amplification for phylogenetic study revealed that the isolate was highly related to Nocardiopsis dassonvillei. In conclusion, these results increased the scope of finding industrially important marine actinomycetes from Visakhapatnam Coastal of Andhra Pradesh.

Exploring Marine Rare Actinomycetes: Untapped Resources of Bioactive Compounds in Clinical Development

Marine Actinomycetes represent a rich and valuable source of distinct and promising substances. The genus Streptomyces in particular, has been extensively studied due to its ability to produce bioactive compounds and its abundance of biosynthetic gene clusters (BGCs). However, the exclusive focus on Streptomyces has resulted in the rediscovery of known compounds. On the other hand, marine rare Actinomycetes (MRA), comprising Actinomycetes species beyond Streptomyces, also harbor a significant number of BGCs. In this article, we summarize the chemical composition, biological activity, and biosynthetic pathways of compounds sourced from MRA that have been tested in clinical trials for their potential in infection, pain relief, and anticancer treatments. Our particular emphasis lies on compounds derived from MRA associated with marine invertebrates, an area that has been comparatively underexplored when compared to MRA isolated from marine sediment and water. Some notable compounds include rifamycin SV, staurosporine, and tetrodotoxin, which are produced by actinomycetes from the genera Salinospora, Micromonospora, and Nocardiopsis. The findings of this overview shed light on the potential of MRA associated with marine invertebrates to yield intriguing compounds that could be developed into drugs. Exploring the natural products from these bacteria holds the promise of discovering novel compounds with remarkable bioactivities.

Antibacterial Effect of Silver Nanoparticles Synthesized from the Secondary Metabolites of Marine Actinomycete Species

Bioprospecting marine actinomycetes can yield biological solutions to many of the key human concerns. The primary reservoir of bioactive metabolites with diverse applications is found in marine actinomycetes. Bioactive secondary metabolites produced by marine actinomycetes are widely used as immunosuppressives, antimicrobials, enzymes, and cosmetics. Actinoplanes, Micromonospora, Saccharopolyspora, Streptomyces, and Amycolatopsis are the main taxonomic groups of actinomycete that are important to industry. Because of the effectiveness of actinomycetes and their bioactive secondary metabolites, modern research is concentrating more on marine actinobacteria to address current difficulties. Nanotechnology combines the concepts of physics, chemistry, and biology to produce particles smaller than 100 nm, or nanoparticles, with specific applications. When it comes to a diverse array of bacteria and fungus, silver nanoparticles have broad spectrum antibacterial characteristics. Within the medical community, silver nanoparticles have become more well-liked because of their antibacterial properties.

Mimicking Nonribosomal Peptides from the Marine Actinomycete Streptomyces sp. H-KF8 Leads to Antimicrobial Peptides.

Microorganisms within the marine environment have been shown to be very effective sources of naturally produced antimicrobial peptides (AMPs). Several nonribosomal peptides were identified based on genome mining predictions of Streptomyces sp. H-KF8, a marine Actinomycetota isolated from a remote Northern Chilean Patagonian fjord. Based on these predictions, a series of eight peptides, including cyclic peptides, were designed and chemically synthesized. Six of these peptides showed antimicrobial activity. Mode of action studies suggest that two of these peptides potentially act on the cell membrane via a novel mechanism allowing the passage of small ions, resulting in the dissipation of the membrane potential. This study shows that though structurally similar peptides, determined by NMR spectroscopy, the incorporation of small sequence mutations results in a dramatic influence on their bioactivity including mode of action. The qualified hit sequence can serve as a basis for more potent AMPs in future studies.

Cytotoxic and Antifungal Staurosporine Derivatives from Marine-Derived Actinomycete Streptomyces sp. ZS-A121.

A novel staurosporine derivate, streptomholyrine A (1), along with 6 known compounds were identified from the rice-based solid fermentation of marine-derived Streptomyces sp. ZS-A121. The planar structure and absolute configuration of streptomholyrine A were elucidated using a combination of 1D, 2D NMR, HRESIMS data analysis, chemical transformation, ECD and NMR calculations. Screening of all these compounds revealed their cytotoxic activity against HCT-116 cell lines, with IC50 values ranging from 0.012 to 11.67 μM, except for the known 1H-indole-3-hydroxyacetyl, which showed no inhibition activity. Furthermore, streptomholyrine A, along with two known staurosporine derivatives, k252d and staurosporine, exhibited activities against Candida albicans, with MICs of 12.5, 25.0 and 50.0 μg/ml, respectively.

Application of laccase produced by marine actinomycetes in accelerating the rate of biodegradation of polyethylene

Although plastic is very useful in modern life, its widespread use could impair human sustainability. Improper plastic waste management generates greenhouse gases and harmful waste. Plastics and its associated by-products, such as microplastics, accumulate on land and in the oceans causing harm to human and ecological health. An environmentally friendly solution, such as enzymes-mediated biocatalytic depolymerization, is required for efficient management of the large amount of waste generated around the world. Actinomycetes are less explored for commercial biodegradation processes but have attracted attention since they constitute a significant proportion of the soil and aquatic flora and because of their ability to degrade complex materials. This study involves identification of laccase-producing marine actinomycetes and examining the possibility of accelerating the rate of biodegradation of polyethylene by treating with laccase enzyme. The polyethylene test material treated with laccase enzyme for 30 days shows 9.36 percent rate of biodegradation, which was six times higher than the rate of biodegradation of an untreated one. The change in the chemical structure of the polyethylene was studied using Fourier transform infrared spectroscopy. After treatment with laccase enzyme, the carbonyl index of the polyethylene test material increased to 1.25 indicating that the polymer was oxidized, and post biodegradation study showed that the carbonyl index decreased to 0.66 which confirms the concept that oxidized polymer was utilized by the microorganisms. The laccase-producing isolate A-09 showed 99 percent identity as Streptomyces rubiginosus based on molecular fingerprinting.

Kueishanamides A and B from the Hydrothermal Vent Sediment Derived Streptomyces sp. WU20.

Marine actinomycetes are known for their production of remarkable organic molecules, particularly those featuring polyoxygenated long-chain backbones. Determining the absolute configurations of these compounds remains a challenging task even today. In this study, we successfully established the planar structures and absolute configurations of two highly flexible amide alkaloids from Streptomyces sp. WU20: kueishanamides A (1) and B (2). These compounds possess a C13 linear backbone and each contains five stereogenic carbon centers. Our approach involved a combination of spectroscopic and computational methods, including J-based configurational analysis and VCD calculations, ensuring the unambiguous determination of their configurations. Kueishanamide A (1) and kueishanamide B (2) showed moderate antifungal activity against pathogenic fungus Crytococcus neoformans, with MIC values of 25 μg/mL each.

Resistomycin Suppresses Prostate Cancer Cell Growth by Instigating Oxidative Stress, Mitochondrial Apoptosis, and Cell Cycle Arrest

Globally, prostate cancer is among the most threatening and leading causes of death in men. This study, therefore, aimed to search for an ideal antitumor strategy with high efficacy, low drug resistance, and no or few adverse effects. Resistomycin is a natural antibiotic derived from marine actinomycetes, and it possesses various biological activities. Prostate cancer cells (PC3) were treated with resistomycin (IC12.5: 0.65 or IC25: 1.3 µg/mL) or 5-fluorouracil (5-FU; IC25: 7 µg/mL) for 24 h. MTT assay and flow cytometry were utilized to assess cell viability and apoptosis. Oxidative stress, apoptotic-related markers, and cell cycle were also assessed. The results revealed that the IC50 of resistomycin and 5-FU on PC3 cells were 2.63 µg/mL and 14.44 µg/mL, respectively. Furthermore, treated cells with the high dose of resistomycin showed an increased number of apoptotic cells compared to those treated with the lower dose. Remarkable induction of reactive oxygen species generation and lactate dehydrogenase (LDH) leakage with high malondialdehyde (MDA), carbonyl protein (CP), and 8-hydroxyguanosine (8-OHdG) contents were observed in resistomycin-treated cells. In addition, marked declines in glutathione (GSH), superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPx) in PC3 cells subjected to resistomycin therapy were observed. Resistomycin triggered observable cell apoptosis by increasing Bax, caspase-3, and cytosolic cytochrome c levels and decreasing Bcl-2 levels. In addition, notable downregulation of proliferating cell nuclear antigen (PCNA) and cyclin D1 was observed in resistomycin-treated cancerous cells. According to this evaluation, the antitumor potential of resistomycin, in a concentration-dependent manner, in prostate cancer cells was achieved by triggering oxidative stress, mitochondrial apoptosis, and cell cycle arrest in cancer cells. In conclusion, our investigation suggests that resistomycin can be considered a starting point for developing new chemotherapeutic agents for human prostate cancer.

Biodiversity and biological applications of marine actinomycetes—Abu-Qir Bay, Mediterranean Sea, Egypt

BackgroundThe ability of actinomycetes to produce bioactive secondary metabolites makes them one of the most important prokaryotes. Marine actinomycetes are one of the most important secondary metabolites producers used for pharmaceuticals and other different industries. ResultsIn this study, the promising actinomycetes were isolated from Abu-Qir Bay. Four different media named as starch nitrate, starch casein, glycerol asparagine, and glycerol glycine were used as a preliminary experimental media to study the role of the medium components on the counts of actinomycetes in sediment samples. The results indicated that starch casein medium reported the highest counts (30–63 CFU/g) in all the tested sites. Lower counts were detected on starch nitrate and glycerol asparagine. On the other hand, glycerol glycine medium gave the lowest counts (15–48 CFU/g). Abu-Qir8 harbored the highest average count of actinomycetes (63 CFU/g), followed by Abu-Qir1 (48 CFU/g). The lower counts were detected in Abu-Qir5 and Abu-Qir7 (26 and 29 CFU/g, respectively). A total of 12 pure obtained actinomycetes isolates were subjected to morphological, physiological, and biochemical characterization. The selected actinobacterial isolates were subjected to numerical analysis, and the majority of isolates were grouped into four main clusters (A, B, C, & D), and each of them harbored two isolates; additionally, four isolates did not cluster at this similarity level. Isolate W4 was carefully chosen as the most promising pigment and antimicrobial agent’s producer; the produced pigment was extracted and optimized by statistical experiments (PBD & BBD) and was tested for its anti-inflammatory activity. The results showed anti-inflammatory effect and prevented the denaturation of BSA protein at a concentration much higher than the safe dose and increased with increasing the pigment concentration. ConclusionMarine actinomycetes play a vital role in the production of novel and important economic metabolites that have many industrial and pharmaceuticals applications. Streptomyces genera are the most important actinomycetes that produce important metabolites as previously reported.

Isolation and Identification of Pigments from Marine Actinomycetes, Along with Their Potential Applications

Natural dyes produced by marine microorganisms particularly actinomycetes—have gained significance as a source of active chemicals and pharmaceuticals with potential for medicinal purposes in recent years. This significant finding served as the foundation for the investigation, which aimed to determine the cytotoxic, antibacterial, and antioxidant properties of a methanolic pigment extract obtained from the marine actinomycetes VES 01 and VES 04. Based on the Brine Shrimp Lethality Test (BSLT), both extracts showed substantial toxicity activity. The actinomycetes VES 01 and VES 04 pigment crude extracts had lethal concentration 50% (LC50) values of 92.64µg/mL and 134.21 mg/mL, respectively, according to the data. When those extracts were evaluated for antibacterial efficacy against a variety of microorganisms, Bacillus subtilis and Escherichia coli showed the best inhibition rates. Additionally, we used 2,2-diphenyl-1-picrylhydrazyl (DPPH) radicals to measure the antioxidant activity. The findings demonstrated that the actinomycetes VES 01 and VES 04 pigment crude extracts had inhibitory concentration 50% (IC50) values of 228.08 µg/mL and 346.3 µg/mL, respectively. We identified the chemical components of actinomycete pigment crude extracts using GC-MS analysis. The results showed that the most prevalent chemicals were 5-Methoxypyrrolidin-2-one (30.23%) for VES 04, 1H-Purine-2,6-dione, and 3,7-dihydro-1,3,7-trimethyl- (CAS) (44.65%) for VES 01 and VES 04. This work showed the antibacterial, antioxidant, and toxicological properties of two pigment crude extracts obtained from actinimycetes actinomycetes VES 01 and VES 04. In terms of antibacterial activity against E. coli ATCC 8739, actnomycete VES 04 pigment crude extract was the most effective, whereas actnomycete VES 01 pigment crude extract revealed the highest level of antioxidant activity.

Nonomuraea corallina sp. nov., isolated from coastal sediment in Samila Beach, Thailand: insights into secondary metabolite synthesis as anticancer potential.

A novel marine actinomycete, designated strain MCN248T, was isolated from the coastal sediment in Songkhla Province, Thailand. Based on the 16S rRNA gene sequences, the new isolate was closely related to Nonomuraea harbinensis DSM45887T (99.2%) and Nonomuraea ferruginea DSM43553T (98.6%). Phylogenetic analyzes based on the 16S rRNA gene sequences showed that strain MCN248T was clustered with Nonomuraea harbinensis DSM45887T and Nonomuraea ferruginea DSM43553T. However, the digital DNA-DNA hybridization analyzes presented a low relatedness of 40.2% between strain MCN248T and the above closely related strains. This strain contained meso-diaminopimelic acid. The acyl type of the peptidoglycan was acetyl, and mycolic acids were absent. The major menaquinones were MK-9(H2) and MK-9(H4). The whole cell sugars consisted of madurose, ribose, mannose, and glucose. Diphosphatidylglycerol, hydroxyl-phosphatidylethanolamine, phosphatidylethanolamine, phosphatidylinositol, and phosphatidylglycerol were detected as the major phospholipids. The predominant cellular fatty acids were iso-C16:0 (40.4%), 10-methyl-C17:0 (22.1%), and C17:18c (10.9%). The DNA G + C content of the genomic DNA was 71.7%. With in silico analyzes, the antiSMASH platform uncovered a diverse 29 secondary metabolite biosynthesis arsenal, including non-ribosomal peptide synthetase (NRPS) and polyketide synthase (PKS) of strain MCN248T, with a high prevalence of gene cluster encoding pathways for the production of anticancer and cytotoxic compounds. Consistently, the crude extract could inhibit colorectal HCT-116 cancer cells at a final concentration of 50 μg/mL. Based on the polyphasic approach, strain MCN248 was designated as a novel species of the genus Nonomuraea, for which the name Nonomuraea corallina sp. nov. is proposed. The type strain of the type species is MCN248T (=NBRC115966T = TBRC17110T).

Phenopyrrolizins A and B, Two Novel Pyrrolizine Alkaloids from Marine-Derived Actinomycetes Micromonospora sp. HU138.

Two previously undescribed pyrrolizine alkaloids, named phenopyrrolizins A and B (1 and 2), were obtained from the fermentation broth of marine-derived Micromonospora sp. HU138. Their structures were established by extensive spectroscopic analysis, including 1D and 2D NMR spectra as well as HRESIMS data. The structure of 1 was confirmed by single-crystal diffraction analysis and its racemization mechanism was proposed. The antifungal activity assay showed that 2 could inhibit the mycelial growth of Botrytis cinerea with the inhibitory rates of 18.9% and 35.9% at 20 μg/disc and 40 μg/disc, respectively.

Natural Products from Marine Actinomycete Genus Salinispora Might Inhibit 3CLpro and PLpro Proteins of SARS-CoV-2: An In Silico Evidence

Among the oldest marine species on the planet, the genus Salinispora is often encountered inhabiting sediments and other marine creatures in tropical and subtropical marine settings. This bacterial genus produces a plethora of natural products. The purpose of this study was to examine the potential for salinispora-based natural products (NPs) to combat the SARS-CoV-2 virus. The RCSB PDB was used to obtain the crystal structures of proteins 3CLpro and PLpro. All 125 NPs were obtained from online databases. Using Autodock Vina software v1.2.0 the molecular docking process was carried out after the proteins and ligands were prepared. Assessments of binding affinities and interacting amino acids were rigorously examined prior to MD simulations. The docking experiments revealed 35 NPs in total for both 3CLpro and PLpro, with high docking scores ranging from −8.0 kcal/mol to −9.0 kcal/mol. However, a thorough binding residue analyses of all docked complexes filtered nine NPs showing strong interactions with HIS: 41 and CYS: 145 of 3CLpro. Whereas, for PLpro, merely six NPs presented good interactions with residues CYS: 111, HIS: 272, and ASP: 286. Further research was conducted on residue–residue and ligand–residue interactions in both the filtered docked complexes and the Apo-protein structures using the Protein Contacts Atlas website. All complexes were found to be stable in CABS-flex 2.0 MD simulations conducted at various time frames (50, 125, 500, and 1000 cycles). In conclusion, salinaphthoquinone B appears to be the most promising metabolite, based on favorable amino acid interactions forming stable confirmations towards 3CLpro and PLpro enzymes, acting as a dual inhibitor.

Isolation and molecular detection of endophytic actinomycetes Nocardiopsis dassonvillei DMS 1 (MH900216) from marine sea grasses with bacterial inactivation

In recent years, new antibiotics have been discovered around the world in order to inhibit multi-drug resistant (MDR) pathogens. To overcome this problem, marine actinomycetes are an alternative choice for producing new bioactive compounds that inhibit MDR bacteria. The typical endophytic actinomycete (EA) Nocardiopsis dassonvillei (N. dassonvillei) DMS 1 (MH900216) was isolated from marine Sea grasses by surface sterilization method. After surface sterilization, it was confirmed that the pure, dry, white-colored spore producing colonies emerged from the internal tissue of the Sea grasses. The crude extract of N. dassonvillei DMS 1 (MH900216) demonstrated 8- and 10-mm zones of inhibition against A. baumannii and K. pneumoniae, respectively. The composition of N. dassonvillei DMS 1 (MH900216) with potential anti-bacterial properties was studied by GC-MS analysis and exhibited 22 chemical compounds. Subsequently, the molecular identification and phylogenetic construction of the isolated EA strain was confirmed as N. dassonvillei DMS 1 (MH900216). The liquid-liquid extraction of the compound demonstrated 24- and 26-mm zones of inhibition against A. baumannii and K. pneumoniae, respectively. Furthermore, the purified crude compound demonstrated 92% and 94% cell death against A. baumannii and K. pneumoniae, respectively, at a minimum inhibitory concentration of 500 μg/mL. Overall, the present study demonstrated the antibacterial properties of the EA N. dassonvillei DMS 1 (MH900216) isolated from Sea grasses and their importance as alternative sources for discovering new antibiotics to inhibit MDR bacteria.

Marine actinomycete Streptomyces variabilis S26 as a biocontrol agent for vibriosis in shrimp larval rearing systems.

Indiscriminate use of antibiotics has led to the emergence of antibiotic-resistant microbes and the loss of natural flora in aquaculture systems necessitating the ban of many of these chemotherapeutants in aquaculture. Actinobacteria play a profound role in the biogeochemical cycling in the marine environment and represent the principal source of secondary metabolites with antimicrobial property. In the present study, 98 marine-derived actinomycete isolates were screened for antimicrobial activity against the common aquatic pathogens. A potent actinomycete isolate S26, identified as Streptomyces variabilis based on 16 S ribosomal RNA (rRNA) gene sequencing was then checked for the production of antibiotic in five different fermentation media and the one which showed maximum production was chosen for further study. Optimization of the fermentation medium for secondary metabolite production was carried out by response surface methodology (RSM) using DESIGN EXPERT. The analysis of variance (ANOVA) of the quadratic regression model demonstrated that the model was highly significant for the response concerned that is, antimicrobial activity as evident from the Fisher's F- test with a very low probability value [(P model>F) = 0.0001]. Of the 10 different solutions suggested by the software, the most suitable composition was found to be starch, 1.38%; soy powder, 0.88%; ammonium sulfate, 0.16% and salinity, 27.76‰. S. variabilis S26 cultured in the optimized production medium was applied in the Penaeus monodon larval rearing system and the total Vibrio count and survival rate were estimated. S. variabilis S26 treatment showed a significant reduction in vibrios and conferred better protection to P. monodon in culture system compared with control.

Production, Purification, Characterization and Anti biofilm activity of natural antibiotic by Actinokineospora cibodasensis from marine water

Health sector faces a distress globally because of the scarcity of newer antibiotics against drug resistant pathogens. Innovations in developing new antibiotics is the solution to combat the drug resistant pathogens. This alarming situation requires advanced, potential and effective antibiotics. Secondary metabolite products from microbes remain as the main origin for many of the antibiotics in the market today and are also found to be promising till date. Out of the microbes, the major share of antibiotic production is reported by Actinomycetes, which are Gram positive, anaerobic, filamentous bacteria. They are currently being exploited through new approaches to improve the efficiency of commercially valuable antibiotics. Since natural environment stands a potential source of innovative and novel antimicrobials, this investigation was performed to test the potential of selected marine actinomycetes. Of the screened ones, Actinokineospora is potential enough to cease the growth of biofilm formation. This strain was identified by molecular characterization as Actinokineospora cibodasensis. It was selected to extract secondary metabolites by submerged fermentation and made to undergo further purification and structural analyses for the search of bioactive components. Presence of streptomycin like compound by Gas Chromatography Mass Spectrometry led to a breakthrough in the study which had been confined by High Performance Thin Layer Chromatography and Fourier Transform Infra-Red Spectroscopy techniques by comparing with standards. Gene expression studies showed that the selected strain can down regulate the genes in the formation of biofilm by the test organism Pseudomonas aeruginosa. The bioactive compound from Actinokineospora is an ecofriendly product along with a biofilm mitigating activity on medical devices. Rare actinomycetal isolate was able to produce the antibiotic which could apply on medical device to reduce the infections during the treatment. This antibiotic coating on life saving devices will provide the ultimate protection for patients.

Evaluation of Antimicrobial Activity by Marine Nocardiopsis dassonvillei against Foodborne Listeria monocytogenes and Shiga Toxin-Producing Escherichia coli.

The emergence of multidrug-resistant pathogens creates public health challenges, prompting a continuous search for effective novel antimicrobials. This study aimed to isolate marine actinomycetes from South Africa, evaluate their in vitro antimicrobial activity against Listeria monocytogenes and Shiga toxin-producing Escherichia coli, and characterize their mechanisms of action. Marine actinomycetes were isolated and identified by 16S rRNA sequencing. Gas chromatography-mass spectrometry (GC-MS) was used to identify the chemical constituents of bioactive actinomycetes' secondary metabolites. Antibacterial activity of the secondary metabolites was assessed by the broth microdilution method, and their mode of actions were predicted using computational docking. While five strains showed antibacterial activity during primary screening, only Nocardiopsis dassonvillei strain SOD(B)ST2SA2 exhibited activity during secondary screening for antibacterial activity. GC-MS identified five major bioactive compounds: 1-octadecene, diethyl phthalate, pentadecanoic acid, 6-octadecenoic acid, and trifluoroacetoxy hexadecane. SOD(B)ST2SA2's extract demonstrated minimum inhibitory concentration and minimum bactericidal concentration, ranging from 0.78-25 mg/mL and 3.13 to > 25 mg/mL, respectively. Diethyl phthalate displayed the lowest bacterial protein-binding energies (kcal/mol): -7.2, dihydrofolate reductase; -6.0, DNA gyrase B; and -5.8, D-alanine:D-alanine ligase. Thus, marine N. dassonvillei SOD(B)ST2SA2 is a potentially good source of antibacterial compounds that can be used to control STEC and Listeria monocytogenes.

Isolation, identification of antimicrobial activity-possessing marine actinomycetes, fungi from samples collected at the Bach Long Vy to Ly Son island

The marine environment has been known as a resource containing a lot of compounds with antibiotic, anti-tuberculosis and antiviral activities. Many of the marine microorganisms have been found to live in sediment, sand, surface or within the body of other living organisms such as sponges, soft coral, mollusk, algae… Natural products from marine actinomyces and fungi are considered an important source for the discovery of novel compounds, of their rich secondary metabolites. From 38 samples collected at 22 coordinates and different depths in the sea from Bach Long Vy island - Hai Phong to Ly Son island - Quang Ngai on the marine research vessel “Oparin Academik”, 40 actinomycetes and 20 fungal strains were isolated. The crude extracts of 60 isolates were primary screened for their antimicrobial activity against 7 pathogenic microorganisms by the Bioassay method in a 96-well tray. As a result, 53/60 strains were resistant at least 1 tested microorganisms, 22/60 isolates against 3 or more the test microorganisms, respectively. In particular, there were 4 isolates (three actinomyces G817, G819, G824 and fungus OM01) with the strongest resistance to four or more tested strains, which were then studied further. The results of phenotypic and molecular identification by 16S rRNA sequences for G817, G819, G824 and 18S rRNA sequence for OM01 showed that OM01 was Penicillium citrinum; G817, G819 strains belonged to Salinispora arenicola, while G824 was identified as Pseudonocardia carboxydivorans. The promising candidate isolates were analyzed in a phylogenetic tree based on MegaX software.

New Insights on Biological Activities, Chemical Compositions, and Classifications of Marine Actinomycetes Antifouling Agents.

Biofouling is the assemblage of undesirable biological materials and macro-organisms (barnacles, mussels, etc.) on submerged surfaces, which has unfavorable impacts on the economy and maritime environments. Recently, research efforts have focused on isolating natural, eco-friendly antifouling agents to counteract the toxicities of synthetic antifouling agents. Marine actinomycetes produce a multitude of active metabolites, some of which acquire antifouling properties. These antifouling compounds have chemical structures that fall under the terpenoids, polyketides, furanones, and alkaloids chemical groups. These compounds demonstrate eminent antimicrobial vigor associated with antiquorum sensing and antibiofilm potentialities against both Gram-positive and -negative bacteria. They have also constrained larval settlements and the acetylcholinesterase enzyme, suggesting a strong anti-macrofouling activity. Despite their promising in vitro and in vivo biological activities, scaled-up production of natural antifouling agents retrieved from marine actinomycetes remains inapplicable and challenging. This might be attributed to their relatively low yield, the unreliability of in vitro tests, and the need for optimization before scaled-up manufacturing. This review will focus on some of the most recent marine actinomycete-derived antifouling agents, featuring their biological activities and chemical varieties after providing a quick overview of the disadvantages of fouling and commercially available synthetic antifouling agents. It will also offer different prospects of optimizations and analysis to scale up their industrial manufacturing for potential usage as antifouling coatings and antimicrobial and therapeutic agents.