Marine Streptomyces as a novel source of bioactive substances

Bioactive Fraction of Streptomyces thinghirensis MSA1 Effectively Inhibits Biofilm Forming Clinically Significant AMR Pathogens

The escalating threat of antibiotic-resistant microorganisms necessitate the discovery of novel antibacterial agents. This study explores the potential of marine-associated actinomycetes, focusing on Streptomyces thinghirensis MSA1, isolated from the marine sponge Callyspongia diffusa in Palk Bay, India, for its notable antibacterial properties. To optimize the production of bioactive compounds of S. thinghirensis MSA1, we established optimal growth conditions (30 °C, pH 7, 2% salinity, 9-day incubation) and utilized ISP4 medium for enhanced secondary metabolite production. The extracted compound, MSA1, was analyzed through FTIR and GCMS, identifying 20 biologically active components. MSA1 demonstrated potent antibacterial activity against significant pathogens, including Escherichia coli, Klebsiella pneumoniae, Salmonella typhi, Pseudomonas aeruginosa, and MRSA, alongside remarkable antioxidant and anti-biofilm properties. These findings highlight the potential of MSA1 as a promising candidate for developing treatments against antibiotic-resistant infections. This study acknowledges the preliminary nature of the findings and the necessity for further in vivo and clinical trials to fully ascertain the therapeutic potential of MSA1. This research opens avenues for novel antibacterial agents in the fight against antibiotic resistance, underscoring the value of marine biodiversity in medical science.

Metabolomic and genomic insights into Micromonospora carbonacea subsp. caeruleus for anti-colorectal compound

Cancer is a predominant contributor to global morbidity and mortality, affecting populations worldwide. Marine Micromonospora species have been identified as significant sources of anticancer compounds. This work aimed to perform a polyphasic approach of isolated strain and conduct comparative metabolomic and genomic analyses to identify compounds with anticancer activity. The study utilized a polyphasic approach on isolated strains for anticancer compound identification. Taxonomic analysis of strain 2MTK254 revealed unique pigment and fatty acid patterns, designating it as a novel Micromonospora carbonacea subsp. caeruleus. Its crude extract displayed significant anti-colorectal activity (66.03% inhibition). Molecular network analysis classified metabolites into eight classes, highlighting a polycyclic tetramate macrolactams (PTMs) compound (P1, C29H38N2O4) with 99.31% inhibitory activity against HCT-116 cell lines (IC50 at 0.125 µM). Genome analysis identified 32 biosynthetic gene clusters (BGCs), including unique PTMs BGCs (83% similarity) linked to the P1 compound. Thus, M. carbonacea subsp. caeruleus 2MTK254 holds promise as a source of novel PTMs with anti-colorectal cancer potential. KEY POINTS: • A novel strain of Micromonospora carbonacea subsp. caeruleus 2MTK254 was isolated in Thailand • A new polycyclic tetramate macrolactam (PTM) with anticancer activity was identified in 2MTK254 • The genome of 2MTK254 has unique secondary metabolite gene clusters.

Diversity of secondary metabolites from marine Streptomyces with potential anti-tubercular activity: a review

The bacterial genus Streptomyces is known for the prolific production of secondary metabolites, which exhibit remarkable structural diversity and potent biological activities. Tuberculosis (TB) remains a formidable global health challenge exacerbated by the emergence of antimicrobial resistance (AMR), necessitating the discovery of novel therapeutic agents. The untapped potential of marine Streptomyces-derived secondary metabolites offers a promising avenue for screening anti-tubercular (anti-TB) compounds with unique chemical structures and potential bioactive properties. The review emphasizes the diverse marine habitats and Streptomyces with novel anti-TB bioactive metabolites. It discusses fermentation and bioprocessing strategies for screening anti-TB drugs. This review also covers the chemical diversity, potency, mechanism of action, and structures of about seventy anti-TB compounds discovered from marine Streptomyces. These compounds span various chemical classes, including quinones, macrolactams, macrolides, phenols, esters, anthracyclines, peptides, glycosides, alkaloids, piperidones, thiolopyrrolones, nucleosides, terpenes, flavonoids, polyketides, and actinomycins. It emphasizes the need to explore marine ecosystems to discover more novel anti-TB natural products.

Optimization and characterization of bioactive secondary metabolites from Streptomyces sp CMSTAAHL-4 isolated from mangrove sediment

BACKGROUND

Ten morphologically different actinomycetes were isolated from mangrove sediments of Manakudy, Kanyakumari District, India. The potent strain was selected based on their primary screening against Gram positive Staphylococcus aureus, Enterococcus faecalis and Gram negative Klebsiella pneumoniae, Escherichia coli, Pseudomonas aeruginosa, Salmonella typhi bacterial pathogens. The selected strain was identified as Streptomyces sp CMSTAAHL-4 by 16S rRNA sequencing. The media optimization for secondary metabolites production was performed by One-Variable at a Time and Response Surface Methodology-Central Composite Design. Minimum inhibitory concentration and minimum bacterial concentration for the extracted secondary metabolites were determined. The antioxidant potential of the secondary metabolites showed that the concentration of the metabolites increases, with the percentage of inhibition. The anti-inflammatory activity of the secondary metabolites found that maximum activity was observed at 500 µg/ml of the metabolites. Alcohols, alkenes, alkynes, alkyl halides, carboxylic acids, aliphatic esters functional groups were identified by fourier transform infrared spectroscopy, gas chromatography and mass spectrometer analysis of the secondary metabolites revealed five bioactive compounds. The X-ray diffraction analysis revealed that the secondary metabolites are amorphous. The thermogravimetric analysis showed the thermal stability of secondary metabolites. Atomic force microscopy analysis revealed specific structural characteristics of the secondary metabolites, which may be associated with their potential biological activities.

CONCLUSIONS

The results showed that the antibacterial, antioxidant, and anti-inflammatory chemicals present in the isolated secondary metabolites give them therapeutic properties.

Naphpyrones A-H, Antibacterial Aromatic Polyketides Isolated from the Streptomyces coelicolor A3(2)/spi1 ΔspiH3

Staphylococcus aureus, a common foodborne pathogen, has a close association with agriculture and food. With the rapid emergence and widespread dissemination of antimicrobial resistance, efforts have been directed toward developing and studying new antimicrobial compounds to inhibit the growth of S. aureus and other foodborne pathogens, thereby preventing contamination and ensuring food safety. Herein, we reported eight new aromatic polyketides, naphpyrones A-H (1-8), from the heterologous expression strain Streptomyces coelicolor A3(2)/spi1 ΔspiH3. Their structures and absolute configurations were elucidated by extensive NMR, MS, theoretical NMR calculations, DP4+ probability analysis, Mosher's method, and ECD analyses. Notably, naphpyrone A (1) featured an unprecedented 6/6/6/6/5 neocyclic skeleton. Bioactivity evaluation revealed that compounds 1 and 2 exhibited antibacterial activity against S. aureus, with MIC values of 1 μg/mL and 4 μg/mL, respectively. These findings highlight the potential for screening and developing therapeutic agents from actinomycetes-derived aromatic polyketides against food pathogens.

Three New Depsipeptides, Homiamides A-C, Isolated from Streptomyces sp., ROA-065

Three new depsipeptides, homiamides A-C (1-3), were isolated from a marine sediment-derived strain of Streptomyces sp., ROA-065. The planar structures of homiamides A-C (1-3) were elucidated using mass spectrometry (MS) and nuclear magnetic resonance (NMR) spectroscopic data. The absolute configurations of 1-3 were deduced from the application of the Marfey's method and GC-MS analysis after formation of the O-trifluoroacetylated (S)-(+)-methyl-2-butyl ester derivatives of amino acids. Compounds 1-3 exhibited weak anti-bacterial activities against both Gram-positive bacteria and Gram-negative bacteria, with compound 1 showing MIC values of 32-64 μg/mL. In antifouling assays, compounds 1 and 2 displayed moderate activity against Micrococcus luteus KCTC 3063, while compound 3 exhibited weak activity against all tested bacteria.

Investigation on taxonomy, secondary metabolites and antibacterial activity of Streptomyces sediminicola sp. nov., a novel marine sediment-derived Actinobacteria

BACKGROUND

Marine actinomycetes, especially Streptomyces, are recognized as excellent producers of diverse and bioactive secondary metabolites on account of the multiplicity of marine habitations and unique ecological conditions, which are yet to be explored in terms of taxonomy, ecology, and functional activity. Isolation, culture and genome analysis of novel species of Streptomyces to explore their potential for discovering bioactive compounds is an important approach in natural product research.

RESULTS

A marine actinobacteria, designated strain SCSIO 75703 T, was isolated, and the potential for bioactive natural product discovery was evaluated based on genome mining, compound detection, and antimicrobial activity assays. The phylogenetic, phenotypic and chemotaxonomic analyses indicate that strain SCSIO 75703 T represents a novel species in genus Streptomyces, for which the name Streptomyces sediminicola sp. nov. is proposed. Genome analysis revealed the presence of 25 secondary metabolite biosynthetic gene clusters. The screening for antibacterial activity reveals the potential to produce bioactive metabolites, highlighting its value for in-depth exploration of chemical constituents. Seven compounds (1-7) were separated from the fractions guided by antibacterial activities, including three indole alkaloids (1-3), three polyketide derivatives (4-6), and 4-(dimethylamino)benzoic acid (7). These primarily antibacterial components were identified as anthracimycin (4), 2-epi-anthracimycin (5) and β-rubromycin (6), presenting strong antibacterial activities against Gram-positive bacteria with the MIC value ranged from 0.125 to 16 μg/mL. Additionally,, monaprenylindole A (1) and 3-cyanomethyl-6-prenylindole (2) displayed moderate inhibitory activities against α-glucosidase with the IC50 values of 83.27 and 86.21 μg/mL, respectively.

CONCLUSION

Strain SCSIO 75703 T was isolated from marine sediment and identified as a novel species within the genus Streptomyces. Based on genomic analysis, compounds isolation and bioactivity studies, seven compounds were identified, with anthracimycin and β-rubromycin showing significant biological activity and promising potential for further applications.

In Silico Analysis and Biochemical Characterization of Streptomyces PET Hydrolase with Bis(2-Hydroxyethyl) Terephthalate Biodegradation Activity

Polyethylene terephthalate (PET), one of the most widely used plastics in the world, causes serious environmental problems. Recently, scientists have been focused on the enzymatic degradation of PET, an environmentally friendly method that offers an attractive approach to the degradation and recycling of PET. In this work, PET hydrolase from Streptomyces sp. W2061 was biochemically characterized, and the biodegradation of PET was performed using the PET model substrate bis (2-hydroxyethyl terephthalate) (BHET). PET hydrolase has an isoelectric point of 5.84, and a molecular mass of about 50.31 kDa. The optimum pH and temperature were 7.0 and 40°C, respectively. LC-MS analysis of the enzymatic products showed that the PET hydrolase successfully degraded a single ester bond of BHET, leading to the formation of MHET. Furthermore, in silico characterization of the PET hydrolase protein sequence and its predicted three-dimensional structure was designed and compared with the well-characterized IsPETase from Ideonella sakaiensis. The structural analysis showed that the (Gly-x1-Ser-x2-Gly) serine hydrolase motif and the catalytic triad (Ser, Asp, and His) were conserved in all sequences. In addition, we integrated molecular dynamics (MD) simulations to analyze the variation in the structural stability of the PET hydrolase in the absence and presence of BHET. These simulations showed the formation of a stable complex between the PET hydrolase and BHET. To the best of our knowledge, this is the first study on Streptomyces sp. W2061 to investigate the BHET degradation activity of PET hydrolase, which has potential application in the biodegradation of plastics in the environment.

Efomycine U, a new C2-asymmetric elaiophylin derivative from Streptomyces malaysiensis DSM 4137

Chemical examination of an actinomycete strain Streptomyces malaysiensis DSM 4137 derived from a soil sample derived isolate Streptomyces sp. DSM 3816, yielded a new C2-asymmetric elaiophylin derivative efomycine U (1) and a known analogue halichoblelide D (2). These structures were unambiguously elucidated on the basis of extensive NMR spectroscopic and mass spectrometric analyses. All compounds isolated were subjected to antimicrobial, cytotoxic and immnosuppressive activities evaluation.

Recent Advances in Marine-Derived Compounds as Potent Antibacterial and Antifungal Agents: A Comprehensive Review

The increase in antimicrobial resistance (AMR) in microorganisms is a significant global health concern. Various factors contribute to AMR, including alterations in cell membrane permeability, increased efflux pump activity, enzymatic modification or inactivation of antibiotics, target site changes, alternative metabolic pathways, and biofilm formation. Marine environments, with their extensive biodiversity, provide a valuable source of natural products with a wide range of biological activities. Marine-derived antimicrobial compounds show significant potential against drug-resistant bacteria and fungi. This review discusses the current knowledge on marine natural products such as microorganisms, sponges, tunicates and mollusks with antibacterial and antifungal properties effective against drug-resistant microorganisms and their ecological roles. These natural products are classified based on their chemical structures, such as alkaloids, amino acids, peptides, polyketides, naphthoquinones, terpenoids, and polysaccharides. Although still in preclinical studies, these agents demonstrate promising in vivo efficacy, suggesting that marine sources could be pivotal in developing new drugs to combat AMR, thereby fulfilling an essential medical need. This review highlights the ongoing importance of marine biodiversity exploration for discovering potential antimicrobial agents.

Discovery of the Lipopeptides Albubactins A-H from Streptomyces albidoflavus RKJM0023 via Chemical Elicitation with Rhamnolipids and Synthesis of Albubactin A

The marine tunicate-derived Streptomyces albidoflavus RKJM0023 was cultured in the presence of a rhamnolipid mixture in an effort to elicit the production of silent natural products. MS/MS-based molecular networking analysis enhanced with nonparametric statistics highlighted the upregulation of a molecular cluster (Kruskal-Wallis p = 1.6 e-6 for 1) in which no MS/MS features had library matches. Targeted isolation of these features resulted in the discovery of nine new N-acylated lipopeptides, albubactins A-H (1-8) each containing a unique glutamine tripeptide and a C-terminal ethyl ester moiety. Three related albubactin acids A-C (9-11) lacking the ethyl ester were also identified. NMR spectroscopy and UPLC-HR-ESI-MS/MS demonstrated that the albubactins were obtained as mixtures that shared a common m/z and differed only in their acylated terminal groups. Due to the complex spectroscopic elucidation with many overlapping shifts, a total synthesis of albubactin A (1) was completed and used to determine the absolute configuration of the new albubactins.

Streptomyces Paradigm in Anticancer Therapy: A State-of-the Art Review

Abstract:

Cancer is one of the biggest threats to human health with a global incidence of 23.6 million, mortality of 10 million, and an estimated 250 million lost in disability-adjusted life years (DALYs) each year. Moreover, the incidence, mortality, and DALYs have increased over the past decade by 26.3%, 20.9%, and 16.0%, respectively. Despite significant evolutions in medical therapy and advances in the DNA microarray, proteomics technology, and targeted therapies, anticancer drug resistance continues to be a growing concern and invites regular discovery of potent agents. One such agent is the microbe-producing bioactive compounds like Streptomyces, which are proving increasingly resourceful in anticancer therapy of the future. Streptomyces, especially the species living in extreme conditions, produce bioactive compounds with cytolytic and anti-oxidative activity which can be utilized for producing anticancer and chemo-preventive agents. The efficacy of the derived compounds has been proven on cell lines and some of these have already established clinical results. These compounds can potentially be utilized in the treatment of a variety of cancers including but not limited to colon, lung, breast, GI tract, cervix, and skin cancer. The Streptomyces, thus possess the armory to fuel the anticancer agents of the future and help address the problem of rising resistance to currently available anti-cancer drugs. We conducted a state-of-art review using electronic databases of PubMed, Scopus, and Google scholar with an objective to appraise the currently available literature on Streptomyces as a source of anti-cancer agents and to compile the clinically significant literature to update the clinicians.

The Complete Genomic Sequence of Microbial Transglutaminase Producer, Streptomyces mobaraensis DSM40587

Actinomycetes are remarkable natural sources of active natural molecules and enzymes of considerable industrial value. Streptomyces mobaraensis is the first microorganism found to produce transglutaminase with broad industrial applications. Although transglutaminase in S. mobaraensis has been well studied over the past three decades, the genome of S. mobaraensis and its secondary metabolic potential were poorly reported. Here, we presented the complete genome of S. mobaraensis DSM40587 obtained from the German Collection of Microorganisms and Cell Cultures GmbH. It contains a linear chromosome of 7,633,041 bp and a circular plasmid of 23,857 bp. The chromosome with an average GC content of 73.49% was predicted to harbour 6683 protein-coding genes, seven rRNA and 69 tRNA genes. Comparative genomic analysis reveals its meaningful genomic characterisation. A comprehensive bioinformatics investigation identifies 35 putative BGCs (biosynthesis gene clusters) involved in synthesising various secondary metabolites. Of these, 13 clusters showed high similarity (> 55%) to known BGCs coding for polyketides, nonribosomal peptides, hopene, RiPP (Ribosomally synthesized and post-translationally modified peptides), and others. Furthermore, these BGCs with over 65% similarity to the known BGCs were analysed in detail. The complete genome of S. mobaraensis DSM40587 reveals its capacity to yield diverse bioactive natural products and provides additional insights into discovering novel secondary metabolites.

Present Status, Limitations, and Prospects of Using Streptomyces Bacteria as a Potential Probiotic Agent in Aquaculture

Streptomyces is a Gram-positive bacterium, belonging to the family Streptomycetaceae and order Streptomycetales. Several strains from different species of Streptomyces can be used to promote the health and growth of artificially cultured fish and shellfish by producing secondary metabolites including antibiotics, anticancer agents, antiparasitic agents, antifungal agents, and enzymes (protease and amylase). Some Streptomyces strains also exhibit antagonistic and antimicrobial activity against aquaculture-based pathogens by producing inhibitory compounds such as bacteriocins, siderophores, hydrogen peroxide, and organic acids to compete for nutrients and attachment sites in the host. The administration of Streptomyces in aquaculture could also induce an immune response, disease resistance, quorum sensing/antibiofilm activity, antiviral activity, competitive exclusion, modification in gastrointestinal microflora, growth enhancement, and water quality amelioration via nitrogen fixation and degradation of organic residues from the culture system. This review provides the current status and prospects of Streptomyces as potential probiotics in aquaculture, their selection criteria, administrative methods, and mechanisms of action. The limitations of Streptomyces as probiotics in aquaculture are highlighted and the solutions to these limitations are also discussed.

(+)- and (-)-Tedanine, a pair of new enantiomeric indolone alkaloids from the marine sponge Tedania sp

(+)- and (-)-Tedanine [(+)-1 and (-)-1], a pair of new enantiomeric indolone alkaloids, along with nine compounds (2-10) were isolated from the marine sponge Tedania sp. The structures of (+)-1 and (-)-1 including absolute configurations were determined by spectroscopic analysis and quantum chemical calculation. Compounds (+)-1 and (-)-1 were the first examples of indolone alkaloids isolated from this genus. In addition, the cytotoxic and antibacterial activities of these compounds were also evaluated.

Streptomyces Diversity Maps Reveal Distinct High-Specificity Biogeographical and Environmental Patterns Compared to the Overall Bacterial Diversity

Despite their enormous impact on the environment and humans, the distribution and variety of the biggest natural secondary metabolite producers, the genus Streptomyces, have not been adequately investigated. We developed representative maps from public EMP 16S rRNA amplicon sequences microbiomics data. Streptomyces ASVs were extracted from the EMP overall bacterial community, demonstrating Streptomyces diversity and identifying crucial diversity patterns. Our findings revealed that while the EMP primarily distinguished bacterial communities as host-associated or free-living (EMPO level 1), the Streptomyces community showed no significant difference but exhibited distinctions between categories in EMPO level 2 (animal, plant, non-saline, and saline). Multiple linear regression analysis demonstrated that pH, temperature, and salinity significantly predicted Streptomyces richness, with richness decreasing as these factors increased. However, latitude and longitude do not predict Streptomyces richness. Our Streptomyces maps revealed that additional samplings in Africa and Southeast Asia are needed. Additionally, our findings indicated that a greater number of samples did not always result in greater Streptomyces richness; future surveys may not necessitate extensive sampling from a single location. Broader sampling, rather than local/regional sampling, may be more critical in answering microbial biogeograph questions. Lastly, using 16S rRNA gene sequencing data has some limitations, which should be interpreted cautiously.

Therapeutic Potential of Marine Probiotics: A Survey on the Anticancer and Antibacterial Effects of Pseudoalteromonas spp

Due to the increasing limitations and negative impacts of the current options for preventing and managing diseases, including chemotherapeutic drugs and radiation, alternative therapies are needed, especially ones utilizing and maximizing natural products (NPs). NPs abound with diverse bioactive primary and secondary metabolites and compounds with therapeutic properties. Marine probiotics are beneficial microorganisms that inhabit marine environments and can benefit their hosts by improving health, growth, and disease resistance. Several studies have shown they possess potential bioactive and therapeutic actions against diverse disease conditions, thus opening the way for possible exploitation of their benefits through their application. Pseudoalteromonas spp. are a widely distributed heterotrophic, flagellated, non-spore-forming, rod-shaped, and gram-negative marine probiotic bacteria species with reported therapeutic capabilities, including anti-cancer and -bacterial effects. This review discusses the basic concepts of marine probiotics and their therapeutic effects. Additionally, a survey of the anticancer and antibacterial effects of Pseudoalteromonas spp. is presented. Finally, marine probiotic production, advances, prospects, and future perspectives is presented.

Statistical optimization and characterization of monodisperse and stable biogenic gold nanoparticle synthesis using Streptomyces sp. M137-2

Microbial synthesis of gold nanoparticles (AuNPs), which are used in various forms with different properties in medicine, as a renewable bioresource has become increasingly important in recent years. In this study, statistical optimization of stable and monodispersed AuNPs synthesis was performed using a cell-free fermentation broth of Streptomyces sp. M137-2 and AuNPs were characterized, and their cytotoxicity was determined. The three factors determined as pH, gold salt (HAuCl₄) concentration, and incubation time, which are effective in the extracellular synthesis of biogenic AuNPs, were optimized by Central Composite Design (CCD) and then UV-Vis Spectroscopy, Dynamic Light Scattering (DLS), X-Ray Diffraction (XRD), Scanning Electron Microscope (SEM), Scanning Transmission Electron Microscope (STEM), size distribution, Fourier-Transform Infrared (FT-IR) Spectroscopy, X-Ray Photoelectron Spectrophotometer (XPS) and stability analyzes of AuNPs were carried out. Optimum values of the factors were determined as pH 8, 10^- 3 M HAuCl₄, and 72 h incubation using Response Surface Methodology (RSM). Almost spherical AuNPs with 20-25 nm protein corona on the surface, 40-50 nm in size, monodisperse, and highly stable form were synthesized. Biogenic AuNPs were confirmed from characteristic diffraction peaks in the XRD pattern, UV-vis peak centred at 541 nm. The FT-IR results confirmed the role of Streptomyces sp. M137-2 metabolites in the reduction and stabilization of AuNPs. The cytotoxicity results also showed that AuNPs obtained using Streptomyces sp. can be used safely in medicine. This is the first report to perform statistical optimization of size-dependent biogenic AuNPs synthesis using a microorganism.

Purification and biochemical characterization of SM14est, a PET-hydrolyzing enzyme from the marine sponge-derived Streptomyces sp. SM14

The successful enzymatic degradation of polyester substrates has fueled worldwide investigation into the treatment of plastic waste using bio-based processes. Within this realm, marine-associated microorganisms have emerged as a promising source of polyester-degrading enzymes. In this work, we describe the hydrolysis of the synthetic polymer PET by SM14est, a polyesterase which was previously identified from Streptomyces sp. SM14, an isolate of the marine sponge Haliclona simulans. The PET hydrolase activity of purified SM14est was assessed using a suspension-based assay and subsequent analysis of reaction products by UV-spectrophotometry and RP-HPLC. SM14est displayed a preference for high salt conditions, with activity significantly increasing at sodium chloride concentrations from 100 mM up to 1,000 mM. The initial rate of PET hydrolysis by SM14est was determined to be 0.004 s^-1 at 45°C, which was increased by 5-fold to 0.02 s^-1 upon addition of 500 mM sodium chloride. Sequence alignment and structural comparison with known PET hydrolases, including the marine halophile PET6, and the highly efficient, thermophilic PHL7, revealed conserved features of interest. Based on this work, SM14est emerges as a useful enzyme that is more similar to key players in the area of PET hydrolysis, like PHL7 and IsPETase, than it is to its marine counterparts. Salt-tolerant polyesterases such as SM14est are potentially valuable in the biological degradation of plastic particles that readily contaminate marine ecosystems and industrial wastewaters.

Draft Genome Sequence of the Marine-Derived, Anticancer Compound-Producing Bacterium Streptomyces sp. Strain GMY01

The marine Streptomyces sp. strain GMY01 was isolated from Indonesian marine sediment. Genome mining analysis revealed that GMY01 has 28 biosynthetic gene clusters, dominated by genes encoding nonribosomal peptide synthetase and polyketide synthase.

Marine‐Derived Hydrogels for Biomedical Applications

Marine organisms provide novel and broad sources for the preparations and applications of biomaterials. Since the urgent requirement of bio‐hydrogels to mimic tissue extracellular matrix (ECM), the natural biomacromolecule hydrogels derived from marine sources have received increasing attention. Benefiting from their outstanding bioactivity and biocompatibility, many attempts have been made to reconstruct ECM components by applying marine‐derived natural hydrogels. Moreover, marine hydrogels have been successfully applied in biomedicine by means of microfluidics, electrospray, and bioprinting. In this review, the classification and characteristics of marine‐derived hydrogels are summarized. In particular, their role in the development of biomaterials is also introduced. Then, the recent advances in bio‐fabrication strategies for various hydrogel materials are focused upon. Besides, the influences of hydrogel types on their functions in biomedical applications are discussed in depth. Finally, critical reflections on the limitations and future development of marine‐derived hydrogels are presented.

Marine Cellulases and their Biotechnological Significance from Industrial Perspectives

Marine microorganisms represent virtually unlimited sources of novel biological compounds and can survive extreme conditions. Cellulases, a group of enzymes that are able to degrade cellulosic materials, are in high demand in various industrial and biotechnological applications, such as in the medical and pharmaceutical industries, food, fuel, agriculture, and single-cell protein, and as probiotics in aquaculture. The cellulosic biopolymer is a renewable resource and is a linearly arranged polysaccharide of glucose, with repeating units of disaccharide connected via β-1,4-glycosidic bonds, which are broken down by cellulase. A great deal of biodiversity resides in the ocean, and marine systems produce a wide range of distinct, new bioactive compounds that remain available but dormant for many years. The marine environment is filled with biomass from known and unknown vertebrates and invertebrate microorganisms, with much potential for use in medicine and biotechnology. Hence, complex polysaccharides derived from marine sources are a rich resource of microorganisms equipped with enzymes for polysaccharides degradation. Marine cellulases' extracts from the isolates are tested for their functional role in degrading seaweed and modifying wastes to low molecular fragments. They purify and renew environments by eliminating possible feedstocks of pollution. This review aims to examine the various types of marine cellulase producers and assess the ability of these microorganisms to produce these enzymes and their subsequent biotechnological applications.

Bioprospecting of endophytic actinobacterium associated with Aloe ferox mill for antibacterial activity

BACKGROUND

The emergence of drug resistance among pathogens has resulted in renewed interest in bioprospecting for natural microbial products.

METHODS

This study aimed to bioprospecting endophytic actinobacterium associated with Aloe ferox Mill for its antibacterial activity. Endophytic actinomycetes were isolated from the gel of A. ferox Mill by surface sterilization technique using actinomycete isolation agar. The isolate with a promising antibacterial activity was identified using 16S rRNA sequence analysis. The minimum inhibitory concentration (MIC) of the extract was assessed by the micro-dilution method and its effect on the respiratory chain dehydrogenase (RCD) activity was ascertained by the iodonitrotetrazolium chloride (INT) assay. Fourier transform-infrared spectrophotometer (FTIR) and gas chromatography-mass spectrophotometry (GC-MS) were employed to identify functional groups and the chemical constituents, respectively.

RESULTS

The actinobacterium was found to be Streptomyces olivaceus CP016795.1. Its extract displayed noteworthy antibacterial activity (MIC ≤1 mg/mL) against Staphylococcus aureus (ATCC 25925), Bacillus cereus (ATCC 10102), and Escherichia coli (ATCC 25922); and showed an inhibitory effect on the RCD activity. FTIR spectrum displayed hydroxyl, amine, and aromatic groups, and the GC-MS revealed 5-Hydroxymethylfurfural as the main constituent (19.47%).

CONCLUSIONS

S. olivaceus CP016795.1 can serve as a potential source of effective antibacterial compounds.

Streptomyces: The biofactory of secondary metabolites

Natural products derived from microorganisms serve as a vital resource of valuable pharmaceuticals and therapeutic agents. Streptomyces is the most ubiquitous bacterial genus in the environments with prolific capability to produce diverse and valuable natural products with significant biological activities in medicine, environments, food industries, and agronomy sectors. However, many natural products remain unexplored among Streptomyces. It is exigent to develop novel antibiotics, agrochemicals, anticancer medicines, etc., due to the fast growth in resistance to antibiotics, cancer chemotherapeutics, and pesticides. This review article focused the natural products secreted by Streptomyces and their function and importance in curing diseases and agriculture. Moreover, it discussed genomic-driven drug discovery strategies and also gave a future perspective for drug development from the Streptomyces.

Halophilic and Halotolerant Actinomycetes of Sambhar Salt Lake, India: Screening and Optimization of Cellulolytic Activity

Actinomycetes are Gram-positive filamentous bacteria well known for the production of bioactive compounds. Recently, many halophilic habitats have been explored for isolation of actinomycetes that exhibit biotechnological potentials. In this investigation, a saline habitat of Rajasthan, Sambhar Salt Lake (SSL) was selected to study the actinomycetes population and Carboxy Methyl Cellulase (CMCase) production by native isolates. A total of sixteen actinomycete isolates, halotolerant and moderately halophilic, were obtained using culture-dependent methods and characterized morphologically and biochemically. They were identified as members of Streptomyces, Nocardiopsis, Pseudonocardia, Saccharospolyspora, and Microbispora. Streptomyces was the most dominating genus, followed by Nocardiopsis. Agar plate assay was used for screening the isolates for CMCase production. Thirteen were found to produce the enzyme, apparent by hydrolysis observed on media plates. The highest relative activity of 22.04 was shown by isolate SSL 14 identified as Nocardiopsis sp. by 16S rDNA sequencing studies and thus selected for further optimization studies. Maximum enzyme (1.08 ± 0.09 U/ml) was produced using medium containing Carboxy Methyl Cellulose (Carbon source) and yeast extract (nitrogen source) at 12% NaCl and pH 9.0, incubated at 30 °C for 96 h. Maximum CMCase production at high salt concentration and pH suggests that Nocardiopsis SSL 14 can be used for industrial processes that operate under excessive saline and alkaline conditions.

Streptothiazolidine B, a new cytotoxic alkaloid produced by Streptomyces violaceoruber

A new cytotoxic alkaloid, named streptothiazolidine B (1), together with three known compounds (2-4), were isolated from Streptomyces violaceoruber. The structure of the undescribed compound was established using 1D and 2D NMR, and HRESIMS. Streptothiazolidine B was isolated and identified as an amide alkaloid with a unique thiazolidine side chain and its absolute configuration was determined by a combination of NOESY experiment and ECD analysis. Streptothiazolidine B exhibited significant cytotoxic activities against two human tumor cell lines, Li-7 and A2780, with IC₅₀ values of 7.8, and 9.1 μM. Meanwhile, compound 4 showed obvious cytotoxic activities against four human tumor cell lines, THP-1, HT29, Li-7 and A2780, with IC₅₀ values ranging from 3.1 to 10.2 μM.

Streptomyces: Still the Biggest Producer of New Natural Secondary Metabolites, a Current Perspective

There is a real consensus that new antibiotics are urgently needed and are the best chance for combating antibiotic resistance. The phylum Actinobacteria is one of the main producers of new antibiotics, with a recent paradigm shift whereby rare actinomycetes have been increasingly targeted as a source of new secondary metabolites for the discovery of new antibiotics. However, this review shows that the genus Streptomyces is still the largest current producer of new and innovative secondary metabolites. Between January 2015 and December 2020, a significantly high number of novel Streptomyces spp. have been isolated from different environments, including extreme environments, symbionts, terrestrial soils, sediments and also from marine environments, mainly from marine invertebrates and marine sediments. This review highlights 135 new species of Streptomyces during this 6-year period with 108 new species of Streptomyces from the terrestrial environment and 27 new species from marine sources. A brief summary of the different pre-treatment methods used for the successful isolation of some of the new species of Streptomyces is also discussed, as well as the biological activities of the isolated secondary metabolites. A total of 279 new secondary metabolites have been recorded from 121 species of Streptomyces which exhibit diverse biological activity. The greatest number of new secondary metabolites originated from the terrestrial-sourced Streptomyces spp.

Sattahipmycin, a Hexacyclic Xanthone Produced by a Marine-Derived Streptomyces

Sattahipmycin was isolated from the mycelium of marine-derived Streptomyces sp. GKU 257-1 by following the antibiofilm activity against E. coli NBRC 3972 throughout the purification steps. The structure of sattahipmycin was determined to be a new polycyclic xanthone related to xantholipin but lacking a dioxymethylene and a chlorinated carbon. This compound showed activity toward Gram-positive bacteria and Plasmodium falciparum, antibiofilm formation of Escherichia coli, and cytotoxicity to human cancer cell lines. Using genome sequence data, a biosynthetic pathway leading to sattahipmycin has been proposed involving an uncharacterized type II polyketide synthase biosynthetic gene cluster.

Streptoglycerides E-H, Unsaturated Polyketides from the Marine-Derived Bacterium Streptomyces specialis and Their Anti-Inflammatory Activity

Four new streptoglycerides E-H (1-4), with a rare 6/5/5/-membered ring system, were isolated from a marine-derived actinomycete Streptomyces specialis. The structures of 1-4 were elucidated by detailed analysis of HRESIMS, 1D and 2D NMR data and ECD spectra as well as comparison of their spectroscopic data with those reported in literature. Compounds 1-4 showed significant anti-inflammatory activity by inhibiting lipopolysaccharide (LPS)-induced nitric oxide (NO) production in Raw 264.7 cells with IC₅₀ values ranging from 3.5 to 10.9 µM. Especially, 2 suppressed mRNA expression levels of iNOS and IL-6 without cytotoxicity.

Antibacterial Meroterpenoids, Merochlorins G-J from the Marine Bacterium Streptomyces sp

Four new chlorinated meroterpenoids, merochlorins G-J (1-4), and 10, a dihydronaphthalenedione precursor, along with known merochlorins A (5) and C-F (6-9), were obtained from cultivation of the bacterium strain Streptomyces sp. CNH-189, which was isolated from marine sediment. The planar structures of compounds 1-4 and 10 were elucidated by interpretation of MS, UV, and NMR spectroscopic data. The relative configurations of compounds 1-4 were determined via analysis of nuclear Overhauser effect (NOE) spectroscopic data, after which their absolute configurations were established by comparing the experimental electronic circular dichroism (ECD) spectra of compounds 1-4 to those of previously reported possible enantiomer models and DP4 calculations. Compound 3 displayed strong antibacterial activities against Bacillus subtilis, Kocuria rhizophila, and Staphylococcus aureus, with MIC values of 1, 2, and 2 μg/mL, respectively, whereas compound 1 exhibited weak antibacterial effects on these three strains, with a 16-32 μg/mL MIC value range.

Complete Genome Sequence of the Marine-Derived Bacterium Streptomyces sp. Strain GMY02

We report the complete genome sequence of Streptomyces sp. strain GMY02, isolated from Indonesian marine sediment. This bacterium has a circular 8,512,626-nucleotide chromosome. Genome mining analysis of the whole-genome sequence revealed that GMY02 has 28 biosynthetic gene clusters, dominated by genes encoding nonribosomal peptide synthetase and polyketide synthase.

Bioactive Secondary Metabolites from Marine Streptomyces griseorubens f8: Isolation, Identification and Biological Activity Assay

Marine actinomycetes are a potential source of a wide variety of bioactive natural products. Herein, four cyclic dipeptides, namely, cyclo(L-Val-L-Pro) (compound 1), cyclo(L-Pro-L-Leu) (compound 2), cyclo(L-Pro-L-Tyr) (compound 3) and cyclo(L-Pro-L-Phe) (compound 5), and an N-acetyltyramine (compound 4) were first isolated and identified as products of the marine Streptomyces griseorubens f8. Compounds 3 and 5 exhibit antibacterial activity against Staphylococcus aureus, Klebsiella aerogenes and Proteus vulgaris. The minimum inhibitory concentrations (MICs) against Staphylococcus aureus, Klebsiella aerogenes and Proteus vulgaris are 160 µg/mL, 100 µg/mL, 120 µg/mL for the compound 3 and 180 µg/mL, 130 µg/mL 150 µg/mL for the compound 5, respectively. In addition, compounds 1, 2, 3 and 5 was first found to have the ability to inhibit the invasion and migration of A549 cells (lung cancer cells), which exhibited the potentiality for these compounds to be used as novel anticancer drugs. This study provides a novel production strain for compounds 1, 2, 3 and 5, and four potential promising anticancer agents.

Streptomyces tardus sp. nov.: A Slow-Growing Actinobacterium Producing Candicidin, Isolated From Sediments of the Trondheim Fjord

Marine environments are home to an extensive number of microorganisms, many of which remain unexplored for taxonomic novelty and functional capabilities. In this study, a slow-growing Streptomyces strain expressing unique genomic and phenotypic characteristics, P38-E01 T , was described using a polyphasic taxonomic approach. This strain is part of a collection of over 8,000 marine Actinobacteria isolates collected in the Trondheim fjord of Norway by SINTEF Industry (Trondheim, Norway) and the Norwegian University of Science and Technology (NTNU, Trondheim, Norway). Strain P38-E01 T was isolated from the sediments of the Trondheim fjord, and phylogenetic analyses affiliated this strain with the genus Streptomyces, but it was not closely affiliated with other described species. The closest related type strains were Streptomyces daliensis YIM 31724 T (98.6%), Streptomyces rimosus subsp. rimosus ATCC 10970 T (98.4%), and Streptomyces sclerotialus NRRL ISP-5269 T (98.3%). Predominant fatty acids were C16:0 iso, C16:0, and Summed Feature 3, and the predominant respiratory quinones were MK-10(H6), MK-10(H4), and MK9(H4). The main polar lipids were identified as diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylglycerol, and phosphoglycolipid. The whole-cell sugars were glucose, ribose, and in minor amounts, mannose. The cell wall peptidoglycan contained LL-diaminopimelic acid. The draft genome has a size of 6.16 Mb, with a %G + C content of 71.4% and is predicted to contain at least 19 biosynthetic gene clusters encoding diverse secondary metabolites. Strain P38-E01 T was found to inhibit the growth of the pathogenic yeast Candida albicans ATCC 90028 and a number of Gram-positive bacterial human and plant pathogens. Metabolites extracted from cultures of P38-E01 T were analyzed by mass spectrometry, and it was found that the isolate produced the antifungal compound candicidin. Phenotypic and chemotaxonomic signatures, along with phylogenetic analyses, distinguished isolate P38-E01 T from its closest neighbors; thus, this isolate represents a novel species of the genus Streptomyces for which the name Streptomyces tardus sp. nov. (P38-E01 T = CCM 9049 T = DSM 111582 T ) is proposed.

Streptomyces poriferorum sp. nov., a novel marine sponge-derived Actinobacteria species expressing anti-MRSA activity

Marine sponges represent a rich source of uncharacterized microbial diversity, and many are host to microorganisms that produce biologically active specialized metabolites. Here, a polyphasic approach was used to characterize two Actinobacteria strains, P01-B04^T and P01-F02, that were isolated from the marine sponges Geodia barretti (Bowerbank, 1858) and Antho dichotoma (Esper, 1794), respectively. Phylogenetic analysis based on 16S rRNA gene sequences indicated that strains P01-B04^T and P01-F02 are closely related to Streptomyces beijiangensis DSM 41794^T, Streptomyces laculatispora NRRL B-24909^T, and Streptomyces brevispora NRRL B-24910^T. The two strains showed nearly identical 16S rRNA gene sequences (99.93%), and the average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) relatedness values were 99.96% and 99.6%, respectively, suggesting that these strains are affiliated with the same species. Chemotaxonomic and culture characteristics of both strains were also consistent with the genus Streptomyces, while phenotypic properties, genome-based comparisons, and phylogenomic analyses distinguished strains P01-B04^T and P01-F02 from their closest phylogenetic relatives. In silico analysis predicted that the 8.9 Mb genome of P01-B04^T contains at least 41 biosynthetic gene clusters (BGCs) encoding secondary metabolites, indicating that this strain could express diverse bioactive metabolites; in support of this prediction, this strain expressed antibacterial activity against Gram-positive bacteria including a clinical isolate of methicillin-resistant Staphylococcus aureus (MRSA) EAMC30. Based on these results, the marine sponge-associated isolates represent a novel species of the genus Streptomyces, for which the name Streptomyces poriferorum sp. nov. is proposed, with P01-B04^T (=DSM 111306^T = CCM 9048^T) as the type strain.

The Genome Analysis of the Human Lung-Associated Streptomyces sp. TR1341 Revealed the Presence of Beneficial Genes for Opportunistic Colonization of Human Tissues

Streptomyces sp. TR1341 was isolated from the sputum of a man with a history of lung and kidney tuberculosis, recurrent respiratory infections, and COPD. It produces secondary metabolites associated with cytotoxicity and immune response modulation. In this study, we complement our previous results by identifying the genetic features associated with the production of these secondary metabolites and other characteristics that could benefit the strain during its colonization of human tissues (virulence factors, modification of the host immune response, or the production of siderophores). We performed a comparative phylogenetic analysis to identify the genetic features that are shared by environmental isolates and human respiratory pathogens. The results showed a high genomic similarity of Streptomyces sp. TR1341 to the plant-associated Streptomyces sp. endophyte_N2, inferring a soil origin of the strain. Putative virulence genes, such as mammalian cell entry (mce) genes were not detected in the TR1341's genome. The presence of a type VII secretion system, distinct from the ones found in Mycobacterium species, suggests a different colonization strategy than the one used by other actinomycete lung pathogens. We identified a higher diversity of genes related to iron acquisition and demonstrated that the strain produces ferrioxamine B in vitro. These results indicate that TR1341 may have an advantage in colonizing environments that are low in iron, such as human tissue.

Isolation and characterization of marine sponge-associated Streptomyces sp. NMF6 strain producing secondary metabolite(s) possessing antimicrobial, antioxidant, anticancer, and antiviral activities

Background

Actinomycetes associated with marine sponge represent a promising source of bioactive compounds. Herein, we report the isolation, identification, and bioactivity evaluation of Streptomyces sp. NMF6 associated with the marine sponge Diacarnus ardoukobae.

Results

Results showed that the strain belonged to the genus Streptomyces, and it was designated as Streptomyces sp. NMF6 with the GenBank accession number MW015111. Ethyl acetate (EtOAc) extract of the strain NMF6 demonstrated a promising antimicrobial activity against Staphylococcus aureus, Enterococcus faecalis, Vibrio damsela, and Candida albicans and a strong antioxidant activity, which were confirmed by DPPH, ferric-reducing power, and phosphomolybdenum assays; results are expressed as ascorbic acid equivalents. NMF6 extract also demonstrated cytotoxicity against breast cancer cell line (MCF-7), hepatocellular carcinoma cell line (Hep-G2), and human colon carcinoma cell line (HCT-116); the selectivity index values were < 2. The extract showed promising antiviral activity against HSV-1, CoxB4, and hepatitis A viruses at concentrations that were nontoxic to the host cells, with the selectivity index values being 13.25, 9.42, and 8.25, respectively. GC-MS analysis of the extract showed the presence of 20 compounds, with bis(2-ethylhexyl) phthalate being the major component (48%).

Conclusions

Our study indicates that the marine sponge–associated Streptomyces sp. NMF6 strain is a potential source of bioactive compounds that could be developed into therapeutic agents.

Flavonoids from Marine-Derived Actinobacteria as Anticancer Drugs

Flavonoids represent a large diverse group of natural products that are used as a traditional medicine against various infectious diseases. They possess many biological activities including antimicrobial, antioxidant, anti-inflammatory, anti-cancer and anti-diabetic activities. Commercially, flavonoids are mainly obtained from plants, however, several challenges are faced during their extraction. Microorganisms have been known as natural sources of a wide range of bioactive compounds including flavonoids. Actinobacteria are the most prolific group of microorganisms for the production of bioactive secondary metabolites, thus facilitating the production of flavonoids. The screening programs for bioactive compounds revealed the potential application of actinobacteria to produce flavonoids with interesting biological activities, especially anticancer activities. Since marine actinobacteria are recognized as a potential source of novel anticancer agents, they are highly expected to be potential producers of anticancer flavonoids with unusual structures and properties. In this review, we highlight the production of flavonoids by actinobacteria through classical fermentation, engineering of plant biosynthetic genes in a recombinant actinobacterium and the de novo biosynthesis approach. Through these approaches, we can control and improve the production of interesting flavonoids or their derivatives for the treatment of cancer.

Anticancer Drug Discovery from Microbial Sources: The Unique Mangrove Streptomycetes

Worldwide cancer incidence and mortality have always been a concern to the community. The cancer mortality rate has generally declined over the years; however, there is still an increased mortality rate in poorer countries that receives considerable attention from healthcare professionals. This suggested the importance of the prompt detection, effective treatment, and prevention strategies. The genus Streptomyces has been documented as a prolific producer of biologically active secondary metabolites. Streptomycetes from mangrove environments attract researchers' attention due to their ability to synthesize diverse, interesting bioactive metabolites. The present review highlights research on mangrove-derived streptomycetes and the production of anticancer-related compounds from these microorganisms. Research studies conducted between 2008 and 2019, specifically mentioning the isolation of streptomycetes from mangrove areas and described the successful purification of compound(s) or generation of crude extracts with cytotoxic activity against human cancer cell lines, were compiled in this review. It is anticipated that there will be an increase in prospects for mangrove-derived streptomycetes as one of the natural resources for the isolation of chemotherapeutic agents.

Marine Actinobacteria Bioflocculant: A Storehouse of Unique Biotechnological Resources for Wastewater Treatment and Other Applications

The bioactive compounds produced by actinobacteria have played a major role in antimicrobials, bioremediation, biofuels, enzymes, and anti-cancer activities. Biodegradable microbial flocculants have been produced by bacteria, algae, and fungi. Microbial bioflocculants have also attracted biotechnology importance over chemical flocculants as a result of degradability and environmentally friendly attributes they possess. Though, freshwater actinobacteria flocculants have been explored in bioflocculation. Yet, there is a paucity of information on the application of actinobacteria flocculants isolated from the marine environment. Similarly, marine habitats that supported the biodiversity of actinobacteria strains in the field of biotechnology have been underexplored in bioflocculation. Hence, this review reiterates the need to optimize culture conditions and other parameters that affect bioflocculant production by using a response surface model or artificial neural network.

Diversity and Bioactive Potential of Actinobacteria Isolated from a Coastal Marine Sediment in Northern Portugal

Natural compounds have had increasing applications in the biotechnological sector, with a large fraction of these substances being channeled to the pharmaceutical industry due to their important pharmacological properties. The discovery of new bioactive molecules with novel mechanisms of action constitutes a promising solution for the design of alternative therapeutic solutions. Actinobacteria are a large group of morphologically and physiologically diverse bacteria well known for their production of biotechnologically relevant compounds. The Portuguese coast is scantly explored in terms of Actinobacteria diversity and respective bioactive potential, offering a good opportunity to find new Actinobacteria taxa and bioactive natural products. In this study, we investigated the Actinobacteria diversity associated with a sediment sample collected from the intertidal zone of a beach in northern Portugal, through a cultivation-dependent approach, and screened its antimicrobial and cytotoxic potential. A total of 52 Actinobacteria strains were recovered from the marine sediment, with the largest fraction of the isolates belonging to the genus Micromonospora. Bioactivity screening assays identified crude extracts of six Streptomyces strains active against C. albicans, exhibiting minimum inhibition concentration (MIC) values in the range of 3.90-125 μg mL^-1. Twenty-five Actinobacteria crude extracts (obtained from strains of the genera Micromonospora, Streptomyces and Actinomadura) exhibited significant effects on the viability of at least one tested cancer cell line (breast ductal carcinoma T-47D and liver hepatocellular carcinoma HepG2). The Actinobacteria extracts demonstrating activity in the antimicrobial and/or cytotoxic assays were subjected to metabolomic analysis (Mass spectrometry (MS)-based dereplication and molecular networking analyses), indicating the presence of four clusters that may represent new natural products. The results obtained demonstrate the importance of bioprospecting underexplored environments, like the Portuguese coast, for enhancing the discovery of new natural products, and call attention to the relevance of preserving the natural genetic diversity of coastal environments.

Antifungal activity of marine-derived actinomycetes against Talaromyces marneffei

AIMS

This study aimed to isolate actinomycetes from marine environments and examine their antifungal activity against Talaromyces marneffei both in vitro and in vivo.

METHODS AND RESULTS

Nineteen out of 101 actinomycete extracts were active and further determined for their minimum inhibitory concentrations (MIC). Three extracts of AMA50 that isolated from sediment showed strong antifungal activity against T. marneffei yeast (MICs ≤0·03-0·25 µg ml^-1 ) and mould (MICs 0·5-16 µg ml^-1 ) forms. The hexane extract from the cells of AMA50 (AMA50CH) exhibited the best activity against both the forms (MIC ≤ 1 µg ml^-1 ). Three extracts from AMA50 killed the melanized yeast cells at 0·5 µg ml^-1 . The AMA50CH was further tested for protective effects in Caenorhabditis elegans model. At concentrations of 1-8 µg ml^-1 , the AMA50CH prolonged survival of T. marneffei-infected C. elegans with a 60-70% survival rate. The composition of AMA50CH was determined by gas chromatography-mass spectrometry. The major components were n-hexadecanoic acid, tetradecanoic acid and pentadecanoic acid. Sequencing analysis revealed that isolate AMA50 belonged to the genus Streptomyces.

CONCLUSIONS

The AMA50CH from Streptomyces sp. AMA50 was the most effective extract against T. marneffei.

SIGNIFICANCE AND IMPACT OF THE STUDY

Talaromyces marneffei is one of the most important thermally dimorphic pathogenic fungi. These results indicated the potency of marine-derived actinomycete extracts against T. marneffei both in vitro and in vivo.

Diversity of Culturable Actinobacteria Producing Protease Inhibitors Isolated from the Intertidal Zones of Maharashtra, India

Phylogenetic diversity of culturable actinobacteria isolated from the intertidal regions of west coast of Maharashtra, India was studied using 16S rRNA gene sequencing. Total of 140 actinobacterial isolates were obtained, which belonged to 14 genera, 10 families and 65 putative species with Streptomyces being the most dominant (63%) genus followed by Nocardiopsis and Micromonospora. Isolates were screened for production of extracellular protease inhibitors (PI) against three pure proteases viz. chymotrypsin, trypsin, subtilisin and a crude extracellular protease from Pseudomonas aeruginosa. Eighty percent of the isolates showed PI activity against at least one of the four proteases, majority of these belonged to genus Streptomyces. Actinobacterial diversity from two sites Ade (17° 52' N, 73° 04' E) and Harnai (17° 48' N, 73° 05' E) with varying anthropological pressure showed that more putative species diversity was obtained from site with lower human intervention i.e. Ade (Shannon's H 3.45) than from Harnai (Shannon's H 2.83), a site with more human intervention. However, in Ade, percentage of isolates not showing PI activity against any of the proteases was close to 21% and that in Harnai was close to 9%. In other words, percentage of PI producers was lower at a site with lesser human intervention.

Draft Genome Sequence of Streptomyces sp. Strain ventii, Isolated from a Microbial Mat near Hydrothermal Vents within the Axial Seamount in the Pacific Ocean, and Resequencing of the Type Strains Streptomyces lonarensis NCL 716 and Streptomyces bohaiensis 11A07

The draft genome of Streptomyces sp. strain ventii, an environmental isolate recovered from deep-sea hydrothermal vents in the Pacific Ocean, is presented along with the resequenced draft genomes of the type strains Streptomyces bohaiensis 11A07 and Streptomyces lonarensis NCL 716.

The draft genome of Streptomyces sp. strain ventii, an environmental isolate recovered from deep-sea hydrothermal vents in the Pacific Ocean, is presented along with the resequenced draft genomes of the type strains Streptomyces bohaiensis 11A07 and Streptomyces lonarensis NCL 716.

Streptomyces-Derived Metabolites with Potential Photoprotective Properties-A Systematic Literature Review and Meta-Analysis on the Reported Chemodiversity

Sun overexposure is associated with the development of diseases that primarily affect the skin, which can lead to skin cancer. Among the main measures of photoprotection is the use of sunscreens. However, there is currently concern about the reported harmful effects to both humans and the environment due to several of the sunscreen ingredients available on the market. For this reason, the search for and development of new agents with photoprotective properties is required. In searching for these metabolites, researchers have turned their attention to microbial sources, especially the microbiota in unusual hostile environments. Among the diverse microorganisms available in nature, Actinobacteria and specifically Streptomyces, have been shown to be a source of metabolites with various biological activities of interest, such as antimicrobial, antitumor and immunomodulator activities. Herein, we present the results of a systematic review of the literature in which Streptomyces isolates were studied as a source of compounds with photoprotective properties. A meta-analysis of the structure-property and structure-activity relationships of those metabolites identified in the qualitative analysis phase was also carried out. These findings indicate that Streptomyces are a source of metabolites with potential applications in the development of new, safe and more eco-friendly sunscreens.

Diversity and antimicrobial potential of Actinobacteria isolated from diverse marine sponges along the Beibu Gulf of the South China Sea

Marine sponge-associated microorganisms have proven to be a very promising source of biologically active and pharmaceutically important natural products. In this study, we investigated the diversity and antibacterial potential of bacteria from 49 sponge species isolated from the Beibu Gulf, South China Sea, belonging to 16 genera and several unidentified taxa. Using a variety of selective media, 363 strains with different morphologies were identified to six bacterial taxa, including Proteobacteria (α-subgroup 85 and γ-subgroup 59), Actinobacteria (123), Firmicutes (90), Bacteroidetes (5) and Brevundimonas (1). Media ISP2 and R2A were the most effective for isolating Actinobacteria. One hundred and twenty-three actinobacterial strains clustered into 21 genera identified by 16S rDNA gene sequencing, most of which were from the genus Microbacterium, followed by Pseudonocardia, Streptomyces, Kocuria, Aeromicrobium, Brachybacterium and Nocardiopsis, constituted 82% of total actinobacterial isolates. By using the minimal medium, 92 actinobacterial isolates showed antimicrobial activities, and 51 strains displayed moderate to strong antimicrobial activity that inhibited the growth of more than half of the bacteria tested in this study. Functional genes related to secondary metabolites were screened, revealing that 10% (12/123) of actinobacterial isolates contained PKS-KS genes, 18% (22/123) harbored NRPS-A genes and 6% (7/123) had hybrid PKS-NRPS gene clusters. The sponges Haliclona sp., Callyspongia sp. and Desmacella sp., belonging to class Demonspongiae, and Leucaltis sp. from the class Calcarea, were dominant hosts, harboring the most diverse actinobacterial genera with stronger antimicrobial activities and more diverse PKS/NRPS genes.