Three new lavandulylated flavonoids, (2S,2″S)-6-lavandulyl-7,4′-dimethoxy-5,2′-dihydroxylflavanone (1), (2S,2″S)-6-lavandulyl-5,7,2′,4′-tetrahydroxylflavanone (2), and (2″S)-5′-lavandulyl-2′-methoxy-2,4,4′,6′-tetrahydroxylchalcone (3), along with seven known compounds 4–10 were isolated from culture broth of Streptomyces sp. G248. Their structures were established by spectroscopic data analysis, including 1D and 2D nuclear magnetic resonance (NMR), and high-resolution electrospray ionization mass spectrometry (HR-ESI-MS). The absolute configurations of 1–3 were resolved by comparison of their experimental and calculated electronic circular dichroism spectra. Compounds 1–3 exhibited remarkable antimicrobial activity. Whereas, two known compounds 4 and 5 exhibited inhibitory activity against Mycobacterium tuberculosis H37Rv with minimum inhibitory concentration (MIC) values of 6.0 µg/mL and 11.1 µg/mL, respectively.

Marine microorganisms are an invaluable source of novel active secondary metabolites possessing various biological activities. In this study, the extraction and isolation of the marine sediment Penicillium species collected in Vietnam yielded ten secondary metabolites, including sporogen AO-1 (1), 3-indolecarbaldehyde (2), 2-[(5-methyl-1,4-dioxan-2-yl)methoxy]ethanol (3), 2-[(2R-hydroxypropanoyl)amino]benzamide (4), 4-hydroxybenzandehyde (5), chrysogine (6), 3-acetyl-4-hydroxycinnoline (7), acid 1H-indole-3-acetic (8), cyclo (Tyr-Trp) (9), and 2’,3’-dihydrosorbicillin (10). Their structures were identified by the analysis of 1D and 2D NMR data. Among the isolated compounds, 2-[(5-methyl-1,4-dioxan-2-yl)methoxy]ethanol (3) showed a strong inhibitory effect against Enterococcus faecalis with a minimum inhibitory concentration value of 32 µg/mL. Both 2-[(2R-hydroxypropanoyl)amino]benzamide (4) and 4-hydroxybenzandehyde (5) selectively inhibited E. coli with minimum inhibitory concentration values of 16 and 8 µg/mL, respectively. 2’,3’-Dihydrosorbicillin (10) potentially inhibited α-glucosidase activity at a concentration of 2.0 mM (66.31%).

The Streptomyces strain G222, isolated from a Vietnamese marine sediment, was confidently identified by 16S rRNA gene sequencing. Its AcOEt crude extract was successfully analyzed using non-targeted LC-MS/MS analysis, and molecular networking, leading to a putative annotation of its chemical diversity thanks to spectral libraries from GNPS and in silico metabolite structure prediction obtained from SIRIUS combined with the bioinformatics tool conCISE (Consensus Annotation Propagation of in silico Elucidations). This dereplication strategy allowed the identification of an interesting cluster of a series of putative cyclic and linear lipopeptides of the lichenysin and surfactin families. Lichenysins (3–7) were isolated from the sub-fraction, which showed significant anti-biofilm activity against Pseudomonas aeruginosa MUC-N1. Their structures were confirmed by detailed 1D and 2D NMR spectroscopy (COSY, HSQC, HMBC, TOCSY, ROESY) recorded in CD₃OH, and their absolute configurations were determined using the modified Marfey’s method. The isolated lichenysins showed anti-biofilm activity at a minimum concentration of 100 µM. When evaluated for antibacterial activity against a panel of Gram-positive and Gram-negative strains, two isolated lichenysins exhibited selective activity against the MRSA strain without affecting its growth curve and without membranotropic activity. This study highlights the power of the MS/MS spectral similarity strategy using computational methods to obtain a cross-validation of the annotated molecules from the complex metabolic profile of a marine sediment-derived Streptomyces extract. This work provides the first report from a Streptomyces strain of combined cyclic and linear lichenysins and surfactins, known to be characteristic compounds of the genus Bacillus.

The marine environmental conditions are particularly different from terrestrial ones; recent studies have showed that marine actinomycetes might produce many novel compounds with good biological activity. The objective of this study is to isolate and screen actinomycetes strains from the marine environment with activity against pathogenic microorganisms. Fifty strains of actinomycetes were isolated from 40 samples including: sediments, sponges, soft corals, echinoderms... collected from Van Phong Bay area of Khanh Hoa province, Vietnam. The strains fermented in A+ medium and fermentation broths were extracted 5 times with ethyl acetate. The extracts were evaporated under reduced pressure to yield crude extracts. Quantitative assay was used to determine MIC (minimum inhibitory concentration) of extract against 7 test strains, including three Gram-negative bacteria (Escherichia coli ATCC25922, Pseudomonas aeruginosa ATCC27853, Salmonella enterica ATCC13076), three Gram-positive bacteria (Enterococcus faecalis ATCC29212, Staphylococcus aureus ATCC25923, Bacillus cereus ATCC 14579), and the yeast Candida albicans ATCC10231. The result of screening showed that: 18/50 strains have shown the antibacterial activities against at least 3 strains of tested microorganisms. In which, strains G650, G654, G657, G666, G675 inhibited three Gram-positive test microorganisms at MIC values from 8 to 64 µg/mL and C. albicans ATCC10231 with MIC values from 2 to 16 µg/mL. In addition, the two strains G657 and G666 had inhibitory effect on P. aeruginosa ATCC27853 và S. enterica ATCC13076 with MIC value 128 µg/mL. Morphological and phylogenetic investigations based on 16S rRNA gene sequences of the selected five strains showed that: strain G650 belonged to species Streptomyces ardesiacus and strain G666 high similarity to the genus Streptomyces; strain G654 showed the highest similarity to the Salinispora arenicola species; strain G657 highest similarity to the Micromonospora aurantiaca; whereas G675 belonged to the Nocardiopsis flavescens species.

In this study, we isolated 46 strains of actinomycetes from 40 samples including: sediments, sponges, soft corals, echinoderms and starfish collected from three sea areas of Vietnam: Thanh Hoa – Quang Binh – Quang Tri. The strains were fermented in A⁺ medium and fermentation broths were extracted 5 times with ethyl acetate then the extracts were evaporated under reduced pressure to yield crude extracts. Quantitative assay was used to determine MIC (Minimum inhibitory concentration) of extract against 7 reference strains. From the results of screening, we chose 5 strains of actinomycetes that have the highest biological activity (Code: G212, G222, G233, G227 and G241). In particular, strains G222, G233, G227 and G241 were resistant 6/7 strains of microorganisms test, with values MICs from 64µg/ml to 256µg/ml; Moreover, All of the five strains were highly resistant to yeast Candida albicans ATCC10231. These strains were then subjected to morphological and phylogenetic investigations based on 16S rRNA gene sequences. The results showed that strains G212, G222 and G227 belonged to Genus Streptomyces; strains G233 and G241 were identified as Genus Micromonospora.

The ocean covers almost three-quarters of our planet’s surface. Marine fungi are fungi that live in marine habitats, most of them are microscopic, either microfungi or yeasts, but many marine species that inhabit the world’s oceans are not known yet. They are well recognized as a source of many novel compounds that possess valuable pharmacological properties. In the present study, we isolated and assessed the antimicrobial and cytotoxic activities of marine fungi isolated from samples collected in Ly Son Island. From 20 samples, a total of 44 marine fungi were isolated. As a result, 33/44 strains were resistant to at least 1 tested microorganisms. Among them, there were 2 isolates VM10 and VM25 showed a broad spectrum of antibacterial activity against five to six tested pathogenic ATCC strains with low MIC values. Moreover, 4/44 extracts (VM10, VM15, VM25, and VM39) showed remarkable cytotoxic effects against HepG2 human hepatoma, MCF-7 breast cancer, and A549 lung cancer cell lines with the recorded viability of tested cancer cells ranging more than 50%. The two candidate strains were subsequently identified as Aspergillus versicolor VM10, Metarhizium sp. VM25 by using 18S rRNA sequence analysis. The promising candidate isolates were analyzed in a phylogenetic tree based on MegaX software.