Streptomyces tirandamycinicus sp. nov., a Novel Marine Sponge-Derived Actinobacterium With Antibacterial Potential Against Streptococcus agalactiae

A smooth vetch (Vicia villosa var.) strain endogenous to the broad-spectrum antagonist Bacillus siamensis JSZ06 alleviates banana wilt disease

Fusarium wilt, caused by Fusarium oxysporum f. sp. cubense Tropical Race 4 (Foc TR4), poses a significant threat to banana production globally, thereby necessitating effective biocontrol methods to manage this devastating disease. This study investigates the potential of Bacillus siamensis strain JSZ06, isolated from smooth vetch, as a biocontrol agent against Foc TR4. To this end, we conducted a series of in vitro and in vivo experiments to evaluate the antifungal activity of strain JSZ06 and its crude extracts. Additionally, genomic analyses were performed to identify antibiotic synthesis genes, while metabolomic profiling was conducted to characterize bioactive compounds. The results demonstrated that strain JSZ06 exhibited strong inhibitory activity against Foc TR4, significantly reducing mycelial growth and spore germination. Moreover, scanning and transmission electron microscopy revealed substantial ultrastructural damage to Foc TR4 mycelia treated with JSZ06 extracts. Genomic analysis identified several antibiotic synthesis genes, and metabolomic profiling revealed numerous antifungal metabolites. Furthermore, in pot trials, the application of JSZ06 fermentation broth significantly enhanced banana plant growth and reduced disease severity, achieving biocontrol efficiencies of 76.71% and 79.25% for leaves and pseudostems, respectively. In conclusion, Bacillus siamensis JSZ06 is a promising biocontrol agent against Fusarium wilt in bananas, with its dual action of direct antifungal activity and plant growth promotion underscoring its potential for integrated disease management strategies.

Taxonomic identification and antagonistic activity of Streptomyces luomodiensis sp. nov. against phytopathogenic fungi

Banana wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) is a devastating fungal disease. Biocontrol strategies hold immense potential for inhibiting the spread of Foc TR4. Here, 30 actinobacteria were isolated from soils and screened for their antagonistic activity against Foc TR4. Strain SCA4-21T was selected due to its strongest antagonistic activity against Foc TR4. Strain SCA4-21T also exhibited strong antagonistic activity against the other eight phytopathogenic fungi. The strain was identified as the genus Streptomyces according to its physiological, biochemical, and phenotypic characteristics. The phylogenetic trees of 16S rRNA sequences demonstrated that strain SCA4-21T formed a subclade with S. iranensis HM 35T and/or S. rapamycinicus NRRL B-5491T with low bootstrap values. Considering that 16S rRNAs did not provide sufficient resolution for species-level identification, the whole genome of strain SCA4-21T was sequenced. Multilocus sequence analysis (MLSA) based on five housekeeping gene alleles (atpD, gyrB, recA, rpoB, and trpB) revealed that strain SCA4-21T clustered into S. hygroscopicus subsp. hygroscopicus NBRC 13472T with 100% of bootstrap value. The analysis of the genome-based phylogeny also approved the results. Average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) were 91.26 and 44.30%, respectively, with values below the respective species level threshold of 95 and 70%. Hence, strain SCA 4-21T represented a novel species within the genus Streptomyces, named Streptomyces luomodiensis sp. nov. The type strain is SCA4-21T (=GDMCC4.340T = JCM36555T). By the CAZymes analysis, 348 carbohydrate-active enzymes (CAZymes) were detected, including 15 chitinases and eight β-1,3-glucanases. The fermentation broth of strain SCA4-21T, exhibiting strong antagonistic activity against Foc TR4, demonstrated high activities of chitinase and β-1,3-glucanase, which might be involved in antifungal activity. Our results showed an innovative potential biocontrol agent for managing plant fungal diseases, specifically banana fusarium wilt.

Streptomyces chengmaiensis sp. nov., isolated from the stem of a mangrove plant in Hainan

A novel Streptomyces strain, designated as HNM0663T, was isolated from the stem of a mangrove plant (Avicennia marina) collected from the coast of Chengmai city, Hainan Island, PR China. On the basis of the alignment of 16S rRNA gene sequences, strain HNM0663T was closely related to Streptomyces lichenis LCR6-01T (98.67 %), Streptomyces nanningensis YIM 33098T (98.12 %) and Streptomyces palmae CMU-AB204T (97.93 %). Genome-based comparisons showed that strain HNM0663T was distinguished from its closest related species with 80.3 % average nucleotide identity and 20.2 % digital DNA-DNA hybridization values. The main cellular fatty acids were iso-C16 : 0, iso-C15 : 0 and anteiso-C15 : 0. The main menaquinones were MK-9 (H6), MK-9 (H4) and MK-8 (H4). The predominant phospholipids contained diphosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol and phosphatidylcholine. Based on these polyphasic taxonomy results, strain HNM0663T should represent a novel Streptomyces species, for which the name Streptomyces chengmaiensis sp. nov. is proposed. The type strain is HNM 0663T (=CCTCC AA 2019075T=LMG 31909T).

Advances in Natural Products from the Marine-Sponge-Associated Microorganisms with Antimicrobial Activity in the Last Decade

Microorganisms are the dominating source of food and nutrition for sponges and play an important role in sponge structure, chemical defense, excretion and evolution. In recent years, plentiful secondary metabolites with novel structures and specific activities have been identified from sponge-associated microorganisms. Additionally, as the phenomenon of the drug resistance of pathogenic bacteria is becoming more and more common, it is urgent to discover new antimicrobial agents. In this paper, we reviewed 270 secondary metabolites with potential antimicrobial activity against a variety of pathogenic strains reported in the literature from 2012 to 2022. Among them, 68.5% were derived from fungi, 23.3% originated from actinomycetes, 3.7% were obtained from other bacteria and 4.4% were discovered using the co-culture method. The structures of these compounds include terpenoids (13%), polyketides (51.9%), alkaloids (17.4%), peptides (11.5%), glucosides (3.3%), etc. Significantly, there are 124 new compounds and 146 known compounds, 55 of which have antifungal activity in addition to antipathogenic bacteria. This review will provide a theoretical basis for the further development of antimicrobial drugs.

New insights into the neuroprotective and beta-secretase1 inhibitor profiles of tirandamycin B isolated from a newly found Streptomyces composti sp. nov

Tirandamycin (TAM B) is a tetramic acid antibiotic discovered to be active on a screen designed to find compounds with neuroprotective activity. The producing strain, SBST2-5^T, is an actinobacterium that was isolated from wastewater treatment bio-sludge compost collected from Suphanburi province, Thailand. Taxonomic characterization based on a polyphasic approach indicates that strain SBST2-5^T is a member of the genus Streptomyces and shows low average nucleotide identity (ANI) (81.7%), average amino-acid identity (AAI) (78.5%), and digital DNA-DNA hybridization (dDDH) (25.9%) values to its closest relative, Streptomyces thermoviolaceus NBRC 13905^T, values that are significantly below the suggested cut-off values for the species delineation, indicating that strain SBST2-5^T could be considered to represent a novel species of the genus Streptomyces. The analysis of secondary metabolites biosynthetic gene clusters (smBGCs) in its genome and chemical investigation led to the isolation of TAM B. Interestingly, TAM B at 20 µg/mL displayed a suppressive effect on beta-secretase 1 (BACE1) with 68.69 ± 8.84% inhibition. Molecular docking simulation reveals the interaction mechanism between TAM B and BACE1 that TAM B was buried in the pocket of BACE-1 by interacting with amino acids Thr231, Asp 228, Gln73, Lys 107 via hydrogen bond and Leu30, Tyr71, Phe108, Ile118 via hydrophobic interaction, indicating that TAM B represents a potential active BACE1 inhibitor. Moreover, TAM B can protect the neuron cells significantly (% neuron viability = 83.10 ± 9.83% and 112.72 ± 6.83%) from oxidative stress induced by serum deprivation and Aβ_1-42 administration models at 1 ng/mL, respectively, without neurotoxicity on murine P19-derived neuron cells nor cytotoxicity against Vero cells. This study was reportedly the first study to show the neuroprotective and BACE1 inhibitory activities of TAM B.

Streptomyces pacificus sp. nov., a novel spongiicolazolicin-producing actinomycete isolated from a coastal sediment

A polyphasic approach was used to determine the taxonomic position of a marine actinomycete, designated isolate CWH03T, which we previously reported to produce new linear azole-containing peptides spongiicolazolicins A and B. Strain CWH03T is mesophilic, neutrophilic, and halotolerant streptomycete that forms spiral spore chains on aerial mycelium. Comparative 16S rRNA gene sequencing showed that CWH03T was most closely related to Streptomyces tirandamycinicus HNM0039T (99.7%), Streptomyces spongiicola HNM0071T (99.4%), 'Streptomyces marianii' ICN19T (99.1%) and Streptomyces wuyuanensis CGMCC4.7042T (99.0%). The phylogenetic tree prepared using the 16S rRNA gene, as well as the phylogenomic tree using the genome BLAST distance phylogeny method and 81 core housekeeping genes, respectively, showed that the closest relative of strain CWH03T was S. spongiicola HNM0071T. The average nucleotide identity and digital DNA-DNA hybridization values between strains CWH03T and S. spongiicola HNM0071T were 91.46% and 44.2%, respectively, which were below the thresholds of 96% and 70% for prokaryotic conspecific assignation. The G+C content of the genomic DNA of strain CWH03T was 72.3%. Whole-cell hydrolysates of strain CWH03T contained LL-diaminopimelic acid. The predominant menaquinone was MK-9(H8) (88.3%), and the major fatty acids were iso-C16:0 (28.4%), anteiso-C15:0 (15.0%) and iso-C15:0 (12.9%). The major phospholipids were diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine and an unidentified phospholipid. Based on data obtained from phenotypic, phylogenetic, genomic, and chemotaxonomic analyses, strain CWH03T represents a novel species of the genus Streptomyces, for which the proposed name is Streptomyces pacificus sp. nov. The type strain is CWH03T ( = NBRC 114659T = TBRC 15780T).

Identification and genomic analyses of a novel endophytic actinobacterium Streptomyces endophytica sp. nov. with potential for biocontrol of yam anthracnose

Anthracnose disease caused by Colletotrichum gloeosporioides is one of the devastating diseases of yams (Dioscorea sp.) worldwide. In this study, we aimed to isolate endophytic actinobacteria from yam plants and to evaluate their potential for the control of yam anthracnose based on bioassays and genomic analyses. A total of 116 endophytic actinomycete strains were isolated from the surface-sterilized yam tissues from a yam orchard in Hainan Province, China. In total, 23 isolates showed antagonistic activity against C. gloeosporioides. An endophytic actinomycete, designated HNM0140^T, which exhibited strong antifungal activities, multiple biocontrol, and plant growth-promoting (PGP) traits was subsequently selected to colonize in the tissue-cultured seedlings of yam and was tested for its in vivo biocontrol potential on yam anthracnose. The results showed that treatment with strain HNM0140^T markedly reduced the severity and incidence of yam anthracnose under greenhouse conditions. Morphological and chemotaxonomic analyses showed that strain HNM0140^T was assigned to the genus Streptomyces. Phylogenetic analysis based on the 16S rRNA gene sequences indicated that strain HNM0140^T formed a separate cluster together with Streptomyces lydicus ATCC 25470^T (99.45%), Streptomyces chattanoogensis NRRL ISP-5002^T (99.45%), and Streptomyces kronopolitis NEAU-ML8^T (98.97%). The phylogenomic tree also showed that strain HNM0140^T stably clustered with Streptomyces lydicus ATCC 25470^T. The ANI and dDDH between strain HNM0140^T and its closest related-type species were well below the recommended thresholds for species demarcation. Hence, based on the phylogenetic, genomic, and phenotypic analyses, strain HNM0140^T should represent a new streptomycete species named Streptomyces endophytica sp. nov. Genomic analysis revealed that strain HNM0140^T harbored 18 putative BGCs for secondary metabolites, some PGP-related genes, and several genes coding for antifungal enzymes. The presented results indicated that strain HNM0140^T was a promising biocontrol agent for yam anthracnose.

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.

Genomic and Biocontrol Potential of the Crude Lipopeptide by Streptomyces bikiniensis HD-087 Against Magnaporthe oryzae

Rice blast caused by Magnaporthe oryzae is one of the most destructive plant diseases. The secondary metabolites of Streptomyces have potential as biological control agents against M. oryzae. However, no commercial secondary antimicrobial products of Streptomyces have been found by gene prediction, and, particularly relevant for this study, a biocontrol agent obtained from Streptomyces bikiniensis has yet to be found. In this research, genomic analysis was used to predict the secondary metabolites of Streptomyces, and the ability to develop biocontrol pharmaceuticals rapidly was demonstrated. The complete genome of the S. bikiniensis HD-087 strain was sequenced and revealed a number of key functional gene clusters that contribute to the biosynthesis of active secondary metabolites. The crude extract of lipopeptides (CEL) predicted by NRPS gene clusters was extracted from the fermentation liquid of S. bikiniensis HD-087 by acid precipitation followed by methanol extraction, and surfactins, iturins, and fengycins were identified by liquid chromatography-mass spectrometry (LC–MS). In vitro, the CEL of this strain inhibited spore germination and appressorial formation of M. oryzae by destroying membrane integrity and through the leakage of cellular components. In vivo, this CEL reduced the disease index of rice blast by approximately 76.9% on detached leaves, whereas its control effect on leaf blast during pot experiments was approximately 60%. Thus, the S. bikiniensis CEL appears to be a highly suitable alternative to synthetic chemical fungicides for controlling M. oryzae.

Beyond the approved: target sites and inhibitors of bacterial RNA polymerase from bacteria and fungi

Covering: 2016 to 2022RNA polymerase (RNAP) is the central enzyme in bacterial gene expression representing an attractive and validated target for antibiotics. Two well-known and clinically approved classes of natural product RNAP inhibitors are the rifamycins and the fidaxomycins. Rifampicin (Rif), a semi-synthetic derivative of rifamycin, plays a crucial role as a first line antibiotic in the treatment of tuberculosis and a broad range of bacterial infections. However, more and more pathogens such as Mycobacterium tuberculosis develop resistance, not only against Rif and other RNAP inhibitors. To overcome this problem, novel RNAP inhibitors exhibiting different target sites are urgently needed. This review includes recent developments published between 2016 and today. Particular focus is placed on novel findings concerning already known bacterial RNAP inhibitors, the characterization and development of new compounds isolated from bacteria and fungi, and providing brief insights into promising new synthetic compounds.

Antibacterial Molecules from Marine Microorganisms against Aquatic Pathogens: A Concise Review

Antibiotic resistance and residues in aquaculture are a growing concern worldwide and consequently identifying favorable antibacterial compounds against aquatic pathogenic bacteria are gained more attention. Active compounds derived from marine microorganisms have shown great promise in this area. This review is aimed to make a comprehensive survey of anti-aquatic pathogenic bacterial compounds that were produced by marine microorganisms. A total of 79 compounds have been reported, covering literature from 1997 to 2021. The compounds are included in different structural classes such as polyketides, terpenoids, nitrogen compounds and others, and some of them present the potential to be developed into agents for the treatment of aquatic pathogenic bacteria.

Biocontrol potential and antifungal mechanism of a novel Streptomyces sichuanensis against Fusarium oxysporum f. sp. cubense tropical race 4 in vitro and in vivo

Most commercial banana cultivars are highly susceptible to Fusarium wilt caused by soilborne fungus Fusarium oxysporum f. sp. cubense (Foc), especially tropical race 4 (TR4). Biological control using antagonistic microorganism has been considered as an alternative method to fungicide. Our previous study showed that Streptomyces sp. SCA3-4 ^T had a broad-spectrum antifungal activity from the rhizosphere soil of Opuntia stricta in a dry hot valley. Here, the sequenced genome of strain SCA3-4 ^T contained 6614 predicted genes with 72.38% of G + C content. A polymorphic tree was constructed using the multilocus sequence analysis (MLSA) of five house-keeping gene alleles (atpD, gyrB, recA, rpoB, and trpB). Strain SCA3-4 ^T formed a distinct clade with Streptomyces mobaraensis NBRC 13819 ^T with 71% of bootstrap. Average nucleotide identity (ANI) values between genomes of strain SCA3-4 ^T and S. mobaraensis NBRC 13819 ^T was 85.83% below 95-96% of the novel species threshold, and named after Streptomyces sichuanensis sp. nov. The type strain is SCA3-4 ^T (= GDMCC 4.214 ^T = JCM 34964 ^T). Genomic analysis revealed that strain SCA3-4 ^T contained 36 known biosynthetic gene clusters of secondary metabolites. Antifungal activity of strain SCA3-4 ^T was closely associated with the production of siderophore and its extracts induced the apoptosis of Foc TR4 cells. A total of 12 potential antifungal metabolites including terpenoids, esters, acid, macrolides etc. were obtained by the gas chromatography-mass spectrometry (GC-MS). Greenhouse experiment indicated that strain SCA3-4 ^T could significantly inhibit infection of Foc TR4 in the roots and corms of banana seedlings and reduce disease index. Therefore, strain SCA3-4 ^T is an important microbial resource for exploring novel natural compounds and developing biopesticides to manage Foc TR4. KEY POINTS: • Strain SCA3-4 ^T was identified as a novel species of Streptomyces. • Siderophore participates in the antifungal regulation. • Secondary metabolites of strain SCA3-4 ^T improves the plant resistance to Foc TR4.

Natural Products from Actinomycetes Associated with Marine Organisms

The actinomycetes have proven to be a rich source of bioactive secondary metabolites and play a critical role in the development of pharmaceutical researches. With interactions of host organisms and having special ecological status, the actinomycetes associated with marine animals, marine plants, macroalgae, cyanobacteria, and lichens have more potential to produce active metabolites acting as chemical defenses to protect the host from predators as well as microbial infection. This review focuses on 536 secondary metabolites (SMs) from actinomycetes associated with these marine organisms covering the literature to mid-2021, which will highlight the taxonomic diversity of actinomycetes and the structural classes, biological activities of SMs. Among all the actinomycetes listed, members of Streptomyces (68%), Micromonospora (6%), and Nocardiopsis (3%) are dominant producers of secondary metabolites. Additionally, alkaloids (37%), polyketides (33%), and peptides (15%) comprise the largest proportion of natural products with mostly antimicrobial activity and cytotoxicity. Furthermore, the data analysis and clinical information of SMs have been summarized in this article, suggesting that some of these actinomycetes with multiple host organisms deserve more attention to their special ecological status and genetic factors.

Identification and Antifungal Mechanism of a Novel Actinobacterium Streptomyces huiliensis sp. nov. Against Fusarium oxysporum f. sp. cubense Tropical Race 4 of Banana

Banana is an important fruit crop. Fusarium wilt caused by Fusarium oxysporum f. sp. cubense tropical race 4 (Foc TR4) seriously threatens the global banana industry. It is difficult to control the disease spread using chemical measures. In addition, commercial resistant cultivars are also lacking. Biological control is considered as a promising strategy using antagonistic microbes. Actinomycetes, especially Streptomyces, are potential sources of producing novel bioactive secondary metabolites. Here, strain SCA2-4 T with strong antifungal activity against Foc TR4 was isolated from the rhizospheric soil of Opuntia stricta in a dry hot valley. The morphological, physiological and chemotaxonomic characteristics of the strain were consistent with the genus Streptomyces. Based on the homology alignment and phylogenetic trees of 16S rRNA gene, the taxonomic status of strain SCA2-4 T exhibited a paradoxical result and low bootstrap value using different algorithms in the MEGA software. It prompted us to further discriminate this strain from the closely related species by the multilocus sequence analysis (MLSA) using five house-keeping gene alleles (atpD, gyrB, recA, rpoB, and trpB). The MLSA trees calculated by three algorithms demonstrated that strain SCA2-4 T formed a distinct clade with Streptomyces mobaraensis NBRC 13819 T . The MLSA distance was above 0.007 of the species cut-off. Average nucleotide identity (ANI) values between strain SCA2-4 T genome and two standard strain genomes were below 95-96% of the novel species threshold. Strain SCA2-4 T was assigned to a novel species of the genus Streptomyces and named as Streptomyces huiliensis sp. nov. The sequenced complete genome of SCA2-4 T encoded 51 putative biosynthetic gene clusters of secondary metabolites. Genome alignment revealed that ten gene clusters were involved in the biosynthesis of antimicrobial metabolites. It was supported that strain SCA2-4 T showed strong antifungal activities against the pathogens of banana fungal diseases. Extracts abstracted from the culture filtrate of strain SCA2-4 T seriously destroyed cell structure of Foc TR4 and inhibited mycelial growth and spore germination. These results implied that strain SCA2-4 T could be a promising candidate for biological control of banana Fusarium wilt.

Biocontrol Ability and Mechanism of a Broad-Spectrum Antifungal Strain Bacillus safensis sp. QN1NO-4 Against Strawberry Anthracnose Caused by Colletotrichum fragariae

Strawberry is a very popular fruit with a special taste, color, and nutritional value. Anthracnose caused by Colletotrichum fragariae severely limits fruit shelf life during post-harvest storage. Use of traditional chemical fungicides leads to serious environment pollution and threatens food safety. Biocontrol is considered as a promising strategy to manage the post-harvest fruit diseases. Here, strain QN1NO-4 isolated from noni (Morinda citrifolia L.) fruit exhibited a high antifungal activity against C. fragariae. Based on its physicochemical profiles and phylogenetic tree of the 16S rRNA sequence, strain QN1NO-4 belonged to the genus Bacillus. The average nucleotide identity (ANI) calculated by comparing two standard strain genomes was below 95-96%, suggesting that the strain might be a novel species of the genus Bacillus and named as Bacillus safensis sp. QN1NO-4. Its extract effectively reduced the incidence of strawberry anthracnose of harvested fruit. Fruit weight and TSS contents were also maintained significantly. The antifungal mechanism assays indicated that the extract of the test antagonist inhibited mycelial growth and spore germination of C. fragariae in vitro. Cells of strain QN1NO-4 demonstrated the cytoplasmic heterogeneity, disappeared organelles, and ruptured ultrastructure. Notably, the strain extract also had a broad-spectrum antifungal activity. Compared with the whole genome of strain QN1NO-4, several functional gene clusters involved in the biosynthesis of active secondary metabolites were observed. Fifteen compounds were identified by gas chromatography-mass spectrometry (GC-MS). Hence, the fruit endophyte B. safensis sp. QN1NO-4 is a potential bio-agent identified for the management of post-harvest disease of strawberry fruit.

Genomic insight into the Streptomyces aurantiacus clade: reclassification of Streptomyces ederensis as a later heterotypic synonym of Streptomyces umbrinus and Streptomyces glomeroaurantiacus as a later heterotypic synonym of Streptomyces aurantiacus

The taxonomic relationships and genome features of the type strains in the Streptomyces aurantiacus clade, including Streptomyces aurantiacus, Streptomyces ederensis, Streptomyces glomeroaurantiacus, Streptomyces umbrinus, Streptomyces phaeochromogenes, Streptomyces dioscori and Streptomyces tauricus, were investigated. Type strains of these species shared high 16S rRNA gene sequence similarity to each other. Multilocus sequence analysis (MLSA) based on atpD, gyrB, recA, rpoB and trpB genes revealed that S. ederensis and S. umbrinus belong to the same species. Also, S. aurantiacus and S. glomeroaurantiacus belong to the same species, but the remaining species are not closely related to each other. MLSA results were verified by the results average nucleotide identity (ANI) and digital DNA-DNA hybridization (dDDH) analyses; while the ANI and dDDH values between S. ederensis and S. umbrinus are 98.1 and 85.4 %, respectively, these values between S. aurantiacus and S. glomeroaurantiacus are 98.9 and 90.7 %, respectively. The presence of almost the same set of biosynthetic gene clusters and highly consistent phenotypic test results also supported the synonymy between S. ederensis and S. umbrinus, as well as between S. aurantiacus and S. glomeroaurantiacus. Therefore, S. ederensis should be reclassified as a later heterotypic synonym of S. umbrinus and S. glomeroaurantiacus should be reclassified as a later heterotypic synonym of S. aurantiacus.

Bioactive Compounds from Marine Sponges: Fundamentals and Applications

Marine sponges are sessile invertebrates that can be found in temperate, polar and tropical regions. They are known to be major contributors of bioactive compounds, which are discovered in and extracted from the marine environment. The compounds extracted from these sponges are known to exhibit various bioactivities, such as antimicrobial, antitumor and general cytotoxicity. For example, various compounds isolated from Theonella swinhoei have showcased various bioactivities, such as those that are antibacterial, antiviral and antifungal. In this review, we discuss bioactive compounds that have been identified from marine sponges that showcase the ability to act as antibacterial, antiviral, anti-malarial and antifungal agents against human pathogens and fish pathogens in the aquaculture industry. Moreover, the application of such compounds as antimicrobial agents in other veterinary commodities, such as poultry, cattle farming and domesticated cats, is discussed, along with a brief discussion regarding the mode of action of these compounds on the targeted sites in various pathogens. The bioactivity of the compounds discussed in this review is focused mainly on compounds that have been identified between 2000 and 2020 and includes the novel compounds discovered from 2018 to 2021.

A Metataxonomic Approach Reveals Diversified Bacterial Communities in Antarctic Sponges

Marine sponges commonly host a repertoire of bacterial-associated organisms, which significantly contribute to their health and survival by producing several anti-predatory molecules. Many of these compounds are produced by sponge-associated bacteria and represent an incredible source of novel bioactive metabolites with biotechnological relevance. Although most investigations are focused on tropical and temperate species, to date, few studies have described the composition of microbiota hosted by Antarctic sponges and the secondary metabolites that they produce. The investigation was conducted on four sponges collected from two different sites in the framework of the XXXIV Italian National Antarctic Research Program (PNRA) in November-December 2018. Collected species were characterized as Mycale (Oxymycale) acerata, Haliclona (Rhizoniera) dancoi, Hemigellius pilosus and Microxina sarai by morphological analysis of spicules and amplification of four molecular markers. Metataxonomic analysis of these four Antarctic sponges revealed a considerable abundance of Amplicon Sequence Variants (ASVs) belonging to the phyla Proteobacteria, Bacteroidetes, Actinobacteria and Verrucomicrobia. In particular, M. (Oxymycale) acerata, displayed several genera of great interest, such as Endozoicomonas, Rubritalea, Ulvibacter, Fulvivirga and Colwellia. On the other hand, the sponges H. pilosus and H. (Rhizoniera) dancoi hosted bacteria belonging to the genera Pseudhongella, Roseobacter and Bdellovibrio, whereas M. sarai was the sole species showing some strains affiliated to the genus Polaribacter. Considering that most of the bacteria identified in the present study are known to produce valuable secondary metabolites, the four Antarctic sponges could be proposed as potential tools for the discovery of novel pharmacologically active compounds.

Streptomyces marianii sp. nov., a novel marine actinomycete from southern coast of India

A novel marine actinomycete strain designated ICN19T was isolated from the subtidal sediment of Chinnamuttam coast of Kanyakumari, India and subjected to polyphasic taxonomic analysis. Neighbour-joining tree based on 16S rRNA gene sequences of validly described type strains had revealed the strain ICN19T formed distinct cluster with Streptomyces wuyuanensis CGMCC 4.7042T, Streptomyces tirandamycinicus HNM0039T and Streptomyces spongiicola HNM0071T. Morphological, physiological and chemotaxonomic characteristics were consistent with those of members of the genus Streptomyces. The strain possessed LL-diaminopimelic acid as the diagnostic diamino acid. The predominant isoprenoid quinone was identified as MK-9(H8) (70%), MK-9(H6) (20%) and MK-9(H2) (2%), with the major cellular fatty acids (>10%) being anteiso-C15:0, C16:0 and iso-C16:0. The main polar lipids were found to be diphosphatidylglycerol, phosphatidylglycerol, phosphatidylethanolamine, phosphatidylinositol mannosides and three unidentified phospholipids. The dendrogram generated on the basis of MALDI-TOF mass spectra supports the strain differentiated from its neigbours. The genome sequence of strain ICN19T was 9,010,366 bp in size with a total of 7420 protein-coding genes and 98 RNA genes. The genomic G+C content of the novel strain was 71.27 mol%. The DNA-DNA relatedness between strain ICN19T and the reference strains with S. wuyuanensis CGMCC 4.7042T, S. tirandamycinicus HNM0039T and S. spongiicola HNM0071T were 42.8%, 39.5% and 38%, respectively. Based on differences in physiological, biochemical, chemotaxonomic differences and whole-genome characteristics the isolated strain represents a novel species of the genus Streptomyces, for which the name Streptomyces marianii sp. nov. is proposed. Type strain is ICN19T (=MCC 3599T = KCTC 39749T).

Newly Isolated Streptomyces sp. JBS5-6 as a Potential Biocontrol Agent to Control Banana Fusarium Wilt: Genome Sequencing and Secondary Metabolite Cluster Profiles

Banana is a key staple food and fruit in countries all over the world. However, the development of the global banana industry is seriously threatened by Fusarium wilt disease, which is caused by Fusarium oxysporum f. sp. cubense (Foc). In particular, Foc tropical race 4 (Foc TR4) could infect more than 80% of global banana and plantain crops. Until now, there were no commercial chemicals or resistant cultivars available to control the disease. Biological control using actinomycetes is considered a promising strategy. In this study, 88 actinomycetes were isolated from a banana orchard without symptoms of Fusarium wilt disease for more than 10 years. An actinobacterial strain labeled as JBS5-6 has exhibited strong antifungal activities against Foc TR4 and other selected 10 phytopathogenic fungi. Based on phenotypic and biochemical traits as well as complete genome analysis, strain JBS5-6 was assigned to Streptomyces violaceusniger. Extracts of the strain inhibited the mycelial growth and spore germination of Foc TR4 by destroying membrane integrity and the ultrastructure of cells. The complete genome of strain JBS5-6 was sequenced and revealed a number of key function gene clusters that contribute to the biosynthesis of active secondary metabolites. Sixteen chemical compounds were further identified by gas chromatography-mass spectrometry (GC-MS). 5-hydroxymethyl-2-furancarboxaldehyde was one of the dominant components in strain JBS5-6 extracts. Moreover, fermentation broth of strain JBS5-6 significantly reduced the disease index of banana seedlings by inhibiting the infection of Foc TR4 in a pot experiment. Hence, strain JBS5-6 is a potential biocontrol agent for the management of disease and the exploitation of biofertilizer.

Isolation and structure determination of new linear azole-containing peptides spongiicolazolicins A and B from Streptomyces sp. CWH03

Linear azole-containing peptides are a class of ribosomally synthesized and post-translationally modified peptides. We performed a chemical investigation on marine actinomycetes, and new linear azole-containing peptides named spongiicolazolicins A and B were found in the MeOH extracts of a newly isolated strain Streptomyces sp. CWH03 (NBRC 114659) and two strains of S. spongiicola (strain HNM0071^T: DSM 103383^T and strain 531S: NBRC 113560). The strain Streptomyces sp. CWH03 was indicated to be a new species closely related to S. spongiicola by phylogenetic analysis using the genome sequence. The new peptides named spongiicolazolicins A and B were isolated from the cell of Streptomyces sp. CWH03. The partial structure of spongiicolazolicin A was determined by 2D NMR experiments. Based on data of MS/MS experiments, the chemical structures of spongiicolazolicins A and B were proposed using the amino acid sequence deduced from the precursor-encoding gene, which was found from whole-genome sequence data of Streptomyces sp. CWH03. The biosynthetic gene cluster of spongiicolazolicins was proposed based on comparative analysis with that of a known linear azole peptide goadsporin. KEY POINTS: • Streptomyces sp. CWH03 was a new species isolated from marine sediment. • New linear azole-containing peptides named spongiicolazolicins A and B were isolated. • Biosynthetic pathway of spongiicolazolicins was proposed.

Genome Mining of the Genus Streptacidiphilus for Biosynthetic and Biodegradation Potential

The genus Streptacidiphilus represents a group of acidophilic actinobacteria within the family Streptomycetaceae, and currently encompasses 15 validly named species, which include five recent additions within the last two years. Considering the potential of the related genera within the family, namely Streptomyces and Kitasatospora, these relatively new members of the family can also be a promising source for novel secondary metabolites. At present, 15 genome data for 11 species from this genus are available, which can provide valuable information on their biology including the potential for metabolite production as well as enzymatic activities in comparison to the neighboring taxa. In this study, the genome sequences of 11 Streptacidiphilus species were subjected to the comparative analysis together with selected Streptomyces and Kitasatospora genomes. This study represents the first comprehensive comparative genomic analysis of the genus Streptacidiphilus. The results indicate that the genomes of Streptacidiphilus contained various secondary metabolite (SM) producing biosynthetic gene clusters (BGCs), some of them exclusively identified in Streptacidiphilus only. Several of these clusters may potentially code for SMs that may have a broad range of bioactivities, such as antibacterial, antifungal, antimalarial and antitumor activities. The biodegradation capabilities of Streptacidiphilus were also explored by investigating the hydrolytic enzymes for complex carbohydrates. Although all genomes were enriched with carbohydrate-active enzymes (CAZymes), their numbers in the genomes of some strains such as Streptacidiphilus carbonis NBRC 100919^T were higher as compared to well-known carbohydrate degrading organisms. These distinctive features of each Streptacidiphilus species make them interesting candidates for future studies with respect to their potential for SM production and enzymatic activities.

Marine Sediment-Derived Streptomyces Strain Produces Angucycline Antibiotics against Multidrug-Resistant Staphylococcus aureus Harboring SCCmec Type 1 Gene

The Philippine archipelago is geographically positioned in the tropics with rich areas of marine biodiversity. Its marine sediments harbor actinomycetes that exhibit antibacterial activity. Screening of actinomycetes isolated from marine sediments collected near the coast of Islas de Gigantes, Iloilo showed one isolate that exhibited high activity against the multidrug-resistant Staphylococcus aureus (MRSA) strain carrying the Staphylococcal Cassette Chromosome mec (SCCmec) type 1 gene, a biomarker for drug resistance. The isolate was identified as Streptomyces sp. strain DSD011 based on its 16s rRNA and protein-coding genes (atpD, recA, rpoB, and trpB) sequences, and was found to be a new species of salt-tolerant marine Streptomyces. Further, the strain harbors both non-ribosomal peptide synthetase (NRPS) and type II polyketide synthase (PKS) in its genome. The targeted chromatographic isolation and chemical investigations by Liquid Chromatography Mass Spectrometry-Time of Flight (LCMS-TOF), tandem mass spectrometry (MS/MS), and Global Natural Product Social molecular networking (GNPS) of the antibiotics produced by the strain afforded the two polycyclic aromatic polyketide angucycline glycosides, fridamycin A (1) and fridamycin D (2), which are products of type II PKS biosynthesis. Compounds 1 and 2 displayed antibacterial activity against MRSA with minimum inhibitory concentration (MIC) of 500 μg/mL and 62.5 μg/mL, respectively. These results suggest that the underexplored marine sediments near the coast of Islas de Gigantes, Iloilo offer access to undiscovered Streptomyces species that are invaluable sources of antibiotic leads.

Streptomyces from traditional medicine: sources of new innovations in antibiotic discovery

Given the increased reporting of multi-resistant bacteria and the shortage of newly approved medicines, researchers have been looking towards extreme and unusual environments as a new source of antibiotics. Streptomyces currently provides many of the world's clinical antibiotics, so it comes as no surprise that these bacteria have recently been isolated from traditional medicine. Given the wide array of traditional medicines, it is hoped that these discoveries can provide the much sought after core structure diversity that will be required of a new generation of antibiotics. This review discusses the contribution of Streptomyces to antibiotics and the potential of newly discovered species in traditional medicine. We also explore how knowledge of traditional medicines can aid current initiatives in sourcing new and chemically diverse antibiotics.

Monitoring and assessment of the therapeutic impact of metabolites extracted from sponge-associated bacteria screened from Gulf of Mannar, southeast coast of India

The present study aimed to assess and monitor the therapeutic potential of antimicrobial metabolites from marine sponge-associated bacteria collected from the southeast coast of India against multidrug-resistant clinical bacterial isolates. Five sponge samples were collected and the metabolite-producing bacteria were screened from the Gulf of Mannar, India, and their antibacterial potential was studied against drug-resistant clinical bacterial isolates obtained from the hospitals. The two metabolite-producing bacteria (IS1 and IS2) were characterized by standard microbiology protocols and 16S rRNA sequencing. The antibacterial metabolites were characterized by liquid chromatography mass spectrometry (LCMS) analysis. The study suggested that marine sponges such as Spheciospongia spp., Haliclona spp., Mycale spp., Tedania spp., and SS-01 were associated with 30 ± 2, 26 ± 2, 23 ± 3, 21 ± 2, and 20 ± 2% of antibacterial metabolite-producing bacteria, respectively. The LCMS analysis of metabolites extracted from IS1 (4,6-dimethyl-2-pyrimidinamine; 4,5-dimethyl-2-propylsilyl-1H-imidazole) and IS2 (caproyl amide, 2-imidazoline) associated with Spheciospongia spp. exhibited significant antibacterial properties against drug-resistant bacteria. IS1 showed antimicrobial potential against the clinical isolates of Proteus spp., and IS2 showed antibacterial potential against isolates of both Proteus mirabilis and Salmonella typhi. IS1 and IS2 were identified by 16S rRNA sequencing and designated as Klebsiella spp. DSCE-bt01 and Pseudomonas spp. DSCE-bt02, respectively. The current study concluded that the assessment and monitoring of novel isolates from sponge-associated bacteria from marine coastal areas probably offer latest breakthrough in curtailing the global antimicrobial resistance and the study of such ecosystems adds value addition to the searching of novel bioactive compounds from terrestrial ecosystems.

The Biological and Chemical Diversity of Tetramic Acid Compounds from Marine-Derived Microorganisms

Tetramic acid (pyrrolidine-2,4-dione) compounds, isolated from a variety of marine and terrestrial organisms, have attracted considerable attention for their diverse, challenging structural complexity and promising bioactivities. In the past decade, marine-derived microorganisms have become great repositories of novel tetramic acids. Here, we discuss the biological activities of 277 tetramic acids of eight classifications (simple 3-acyl tetramic acids, 3-oligoenoyltetramic acids, 3-decalinoyltetramic acid, 3-spirotetramic acids, macrocyclic tetramic acids, N-acylated tetramic acids, α-cyclopiazonic acid-type tetramic acids, and other tetramic acids) from marine-derived microbes, including fungi, actinobacteria, bacteria, and cyanobacteria, as reported in 195 research studies up to 2019.