Metabolites from Lysobacter gummosus YMF3.00690 Against Meloidogyne javanica.

The strains in Lysobacter spp. have the potential to control plant-parasitic nematodes. In our experiment, L. gummosus YMF3.00690 showed antagonistic effects against plant root-knot nematode. Nine metabolites were isolated and identified from cultures of L. gummosus YMF3.00690, of which compound 1 was identified as a new metabolite tetrahydro-4,4,6-trimethyl-6-[(tetrahydro-6,6-dimethyl-2-oxo-4(1H)-pyrimidinylidene) methyl]-2(1H)-pyrimidinone. The activity assay showed that two compounds, 5-(hydroxymethyl)-1H-pyrrole-2-carbaldehyde (2) and 1H-pyrrole-2-carboxylic acid (3), had nematicidal activities against Meloidogyne javanica with mortalities of 69.93 and 90.54% at 400 ppm for 96 h, respectively. These two compounds were further tested for the inhibition activity of eggs hatching, and compound 3 showed a significant inhibition rate of 63.36% at 50 ppm for 48 h. In the chemotactic activity assay, three compounds (1 to 3) were found to have concentration-dependent chemotactic activity, of which compound 1 showed attractive activity. This experiment explored the active metabolites of L. gummosus YMF3.00690 against M. javanica and laid the foundation for biopesticide development.

Stereumamides E-H, four new minor quaternary ammonium hybrids from Stereum hirsutum.

In our preview research, four novel quaternary ammonium hybrids were isolated from the Stereum hirsutum FP-91666. To further discover this type of compounds, S. hirsutum was fermented in 30 L YMG broth, and eight hybrid compounds including four new quaternary ammoniums were obtained, which are sesquiterpenes combined with α-amino acids. Their structures were elucidated by extensive spectroscopic analyses, including 1D- and 2D-NMR, and HR-MS experiments.

Identification and Mechanism of Action of the Global Secondary Metabolism Regulator SaraC in Stereum hirsutum.

DNA methylation is an important factor in the regulation of gene expression. In analyzing genomic data of Stereum hirsutum FP-91666, we found a hypothetical bifunctional transcription regulator/O6Meguanine-DNA methyltransferase (named SaraC), which is widely present in both bacteria and fungi, and confirmed that its function in bacteria is mainly for DNA reparation. In this paper, we confirmed that SaraC has the function of DNA binding and demethylation through surface plasma resonance and reaction experiments in vitro. Then, we achieved the overexpression of SaraC (OES) in S. hirsutum, sequenced the methylation and transcription levels of the whole-genome, and further conducted untargeted metabolomics analyses of the OES transformants and the wild type (WT). The results confirmed that the overall-methylation levels of the transformants were significantly downregulated, and various genes related to secondary metabolism were upregulated. Through comparative untargeted metabolomic analyses, it showed that OES SA6 transformant produced a greater number of hybrid polyketides, and we identified 2 novel hybrid polyketides from the fermentation products of SA6. Our results show that overexpression SaraC can effectively stimulate the expression of secondary-metabolism-related genes, which could be a broad-spectrum tool for discovery of metabolites due to its cross-species conservation. IMPORTANCE Fungi are one of the important sources of active compounds. However, in fungi, most of the secondary metabolic biosynthetic gene clusters are weakly expressed or silenced under conventional culture conditions. How to efficiently excavate potential new compounds contained in fungi is becoming a research hot spot in the world. In this study, we found a DNA demethylation protein (SaraC) and confirmed that it is a global secondary metabolism regulator in Stereum hirsutum FP-91666. In the past, SaraC-like proteins were mainly regarded as DNA repair proteins, but our findings proved that it will be a powerful tool for mining secondary metabolites for overexpression of SaraC, which can effectively stimulate the expression of genes related to secondary metabolism.

Sesquiterpenoids and their quaternary ammonium hybrids from the mycelium of mushroom Stereum hirsutum by medium optimization.

The fungal genus Stereum (Stereaceae) produces a broad variety of specialised metabolites, including a wide range of terpenes. This probably relates to the presence of an extensive biosynthetic machinery for this group of compounds: genomic analysis of Stereum hirsutum has identified 16 terpene synthase gene clusters, 6 polyketide synthase gene clusters, and 1 polyketide synthase non-ribosomal polypeptide heterodimer gene cluster in S. hirsutum FP-91666. In the present study, the One Strain Many Compounds (OSMAC) approach was employed to discover undescribed metabolites from this strain. Fermentation was carried out in five media and the products of the strain cultivated on different media were analyzed by LC-MS. From cultures grow in WGB medium (30.0 g wheat bran, 20.0 g glucose, 1.5 g KH2PO4, and 1.5 g MgSO4), four previously undescribed metabolites, a sesquiterpene sterostrein X and three mixed terpenes (stereumamides I-K) were isolated, together with seven known compounds (drimene-2,11-diol, stereumamide E, stereumamide D, stereumamide B, stereumamide A, stereumamide C, and sterostrein Q). The drimane-type sesquiterpene drimene-2,11-diol was found in S. hirsutum FP-91666 for the first time. All structures were elucidated by spectroscopic data analysis. The absolute configurations of stereumamides I, J and K were assigned by comparing their experimental and calculated electronic circular dichroism (ECD) spectra. An anti-Mycobacterium tuberculosis experiment showed that stereumamides I-K and sterostrein Q had weak antibacterial activity against this pathogen.

Antibacterial diketopiperazines from an endophytic fungus Bionectria sp. Y1085.

Two new diketopiperazines (1, 2), one new polyprenol (3), together with 19 known compounds (4-22) were obtained from the EtOAc extract of Bionectria sp. Y1085, an endophytic fungus isolated from the plant Huperzia serrata. Their structures were elucidated by extensive NMR and MS analysis. Bionectin D (1) is a rare diketopiperazine with a single methylthio substitution at the α-carbon of cyclized amino acid residue. The antibacterial activity of compounds was assayed against Escherichia coli, Staphylococcus aureus, and Salmonella typhimurium ATCC 6539, and some metabolites (1, 2, 10, 11, and 14) exhibited evident antibacterial activity.