Diversity and bioprospecting of culturable actinomycetes from marine sediment of the Yellow Sea, China.

Marine actinomycetes are a potential source of a wide variety of bioactive natural products. In this work, seven pretreatments, three selective isolation media, and five artificial seawater concentrations were used to isolate actinomycetes from the sediments collected from Yellow Sea, China. Statistical analysis showed that only the isolation medium strongly affected the total and bioactive numbers of actinomycete isolates. A total of 613 actinobacterial strains were isolated and screened for antimicrobial activities; 154 isolates showed activity against at least one of nine test drug-resistant microorganisms. Eighty-nine representatives with strong antimicrobial activity were identified phylogenetically based on 16S rRNA gene sequencing, which were assigned to five different actinomycete genera Streptomyces, Kocuria, Saccharomonospora, Micromonospora, and Nocardiopsis. Using PCR-based screening for six biosynthetic genes of secondary metabolites, all 45 isolates with acute activity have at least one biosynthetic gene, 28.8 % of which possess more than three biosynthetic genes. As a case, strain SMA-1 was selected for antimicrobial natural product discovery. Three diketopiperazine dimers including a new compound iso-naseseazine B (1) and two known compounds naseseazine B (2) and aspergilazine A (3) were isolated by bioassay-guided separation. These results suggested that actinomycetes from marine sediments are a potential resource of novel secondary metabolites and drugs.

Endophytes in the plant Huperzia serrata: fungal diversity and discovery of a new pentapeptide.

Endophytic fungi are an underexploited resource of natural products and have a capacity to produce diverse classes of plant-derived secondary metabolites. Here, we investigated the diversity of endophytic fungi from Huperzia serrata and the potential for discovering novel fungal natural products. One hundred and fifty-five endophytic fungi isolates obtained from H. serrata, belonging to four classes Dothideomycetes (47.3 %), Sordariomycetes (36.8 %), Eurotiomycetes (10.6 %) and an undefined class (5.3 %, Mucoraceae), were grouped into nine genera based on morphological and molecular identification. Colletotrichum, Cladosporium, Sordariomycetes and Guignardia were the dominant genera, whereas the remaining genera were infrequent groups. To our knowledge, the fungal genera Mucor and Neurospora were first reported in Huperzia plant. Among these endophytic fungi isolates, strain B14, belonging to Penicillium oxalicum, gave a gray precipitate with Dragendorff's reagent. A new pentapeptide was isolated from the culture of strain B14, and its chemical structure was elucidated on the basis of spectroscopic data from (1)H NMR, (13)C NMR and ESI-MS/MS. Taken together, H. serrata has a significant diversity of endophytic fungi that could be a rich resource for the discovery of new natural products.

Synthesis and insecticidal evaluation of novel N-pyridylpyrazolecarboxamides containing an amino acid methyl ester and their analogues.

On the basis of the commercial insecticide chlorantraniliprole, a series of novel N-pyridylpyrazolecarboxamides containing an amino acid methyl ester and their analogues were designed and synthesized. Their chemical structures were established on the basis of corresponding (1) H NMR spectroscopy, (13)C NMR spectroscopy, elemental analysis, and single-crystal X-ray diffraction analysis. The insecticidal activities of the new compounds against oriental armyworm ( Mythimna separata ) and diamondback moth ( Plutella xylostella ) were evaluated. The results of bioassays indicated that most of the compounds showed moderate to high activities at the tested concentration, of which the compounds 6 containing a methyl acrylate substructure had excellent larvicidal activity; for example, 6a displayed 100% larvicidal activity against P. xylostella at the concentration of 0.005 mg/L, whereas the activities of both compounds 6g and 6h against M. separata were 100% at 2.5 mg/L. The calcium imaging technique experiment results showed that novel compound 6 could elevate the calcium concentration in the cytoplasm. Furthermore, this study also provided evidence that compound 6h activates inositol 1,4,5-trisphosphate (IP3) sensitive intracellular calcium release channels in the endoplasmic reticulum of Spodoptera exigua third-instar larva neurons.