Characterization and biocontrol mechanism of Streptomyces olivoreticuli as a potential biocontrol agent against Rhizoctonia solani.

Rhizoctonia solani is a widespread and devastating plant pathogenic fungus that infects many important crops. This pathogen causes tobacco target spot, a disease that is widespread in many tobacco-growing countries and is destructive to tobacco. To identify antagonistic microorganisms with biocontrol potential against this disease, we isolated Streptomyces strains from forest inter-root soil and screened a promising biocontrol strain, ZZ-21. Based on in vitro antagonism assays, ZZ-21 showed a significant inhibitory effect on R. solani and various other phytopathogens. ZZ-21 was identified as Streptomyces olivoreticuli by its phenotypic, genetic, physiological and biochemical properties. Complete genome sequencing revealed that ZZ-21 harbored numerous antimicrobial biosynthesis gene clusters. ZZ-21 significantly reduced the lesion length in detached inoculated leaf assays and reduced the disease index under greenhouse and field conditions. Based on an in vitro antagonistic assay of ZZ-21 culture, the strain exhibited an antifungal activity against R. solani in a dose-dependent manner. The culture filtrate could impair membrane integrity, possibly through membrane lipid peroxidation. ZZ-21 could secrete multiple extracellular enzymes and siderophores. According to a series of antifungal assays, the extracellular metabolites of ZZ-21 contained antimicrobial bioactive compounds composed of proteins/peptides extracted using ammonium sulfate precipitation, which were stable under stress caused by high temperature and protease K. The EC50 value for ammonium sulfate precipitation was determined to be 21.11 µg/mL in this study. Moreover, the proteins/peptides also exhibited biocontrol ability and were observed to alter the plasma membrane integrity of R. solani which were evaluated by biocontrol efficacy assays on detached tobacco leaves and PI staining. Overall, strain ZZ-21 shows the potential to be developed into a biopesticide against tobacco target spot disease.

Characterization of a novel victorivirus from Nigrospora chinensis, a fungus isolated from tobacco.

Here, we characterized a new mycovirus from the fungus Nigrospora chinensis, which was named "Nigrospora chinensis victorivirus 1" (NcVV1). The NcVV1 genome is 5283 bp in length, containing two continuous open reading frames (ORFs), ORF1 and ORF2. ORF1 and ORF2 were predicted to encode a putative coat protein (CP) and an RNA-dependent RNA polymerase (RdRp), respectively. The stop codon of ORF1 overlaps with the start codon of ORF2 by the tetranucleotide sequence AUGA. Phylogenetic analysis based on amino acid sequences of RdRp and CP indicated that NcVV1 clustered with members of the genus Victorivirus in the family Totiviridae. To our knowledge, this was the first report of a mycovirus infecting N. chinensis.

[Study on the mechanism of polypeptide extract from scorpion venom on inhibition of angiogenesis of H 22 hepatoma].

OBJECTIVE: To explore the mechanism of polypeptide extract from scorpion venom (PESV) on inhibiting angiogenesis. METHODS: The H22 hepatoma tumor model was established by subcutaneously implanting H22 hepatoma cells into mice. The tumor-bearing mice were randomly divided into 4 groups, i.e., the control group, the high dose PESV group, the low dose PESV group, and the 5-fluorouracil (5-Fu) group, 10 mice in each group. The intervention was lasted for 14 days. The growth curve of the tumor volume was drawn and the inhibition rate calculated. Pathological changes of the tumors were observed by HE staining. The microvessel density (MVD) was detected using SP method. The protein expression levels of phosphatidylinositol 3-kinase (P13K), phosphoprotein kinase B (P-Akt), hypoxia-inducible factor-1 alpha (HIF-1 )alpha, and vascular endothelial growth factor-A (VEGF-A) were detected by immunohistochemical assay and Western blot. RESULTS: The tumor inhibitory rate was 64.8%, 43.7%, and 32.4% in the 5-Fu group, the high dose PESV group, and the low dose PESV group. Compared with the control group, the protein expression of PI3K, P-Akt, HIF-1alpha, and VEGF-A were obviously inhibited by PESV and 5-Fu (P <0. 05,P <0. 01). The MVD also decreased in the high and low dose PESV groups (P < 0.05). CONCLUSIONS: PESV could inhibit the angiogenesis of H22 hepatoma. The mechanisms might be associated with suppressing the expression of PI3K, P-Akt, HIF-1 alpha, and VEGF-A.