Complete genome sequence of the Pogostemon cablin bacterial wilt pathogen Ralstonia solanacearum strain SY1.

BACKGROUND: Ralstonia solanacearum causes bacterial wilt of Pogostemon cablin which is an important aromatic herb and also the main materials of COVID-19 therapeutic traditional drugs. However, we are lacking the information on the genomic sequences of R. solanacearum isolated from P. cablin. OBJECTIVE: The acquisition and analysis of this whole-genome sequence of the P. cablin bacterial wilt pathogen. METHODS: An R. solanacearum strain, named SY1, was isolated from infected P. cablin plants, and the complete genome sequence was sequenced and analyzed. RESULTS: The SY1 strain contains a 3.70-Mb chromosome and a 2.18-Mb megaplasmid, with GC contents of 67.57% and 67.41%, respectively. A total of 3308 predicted genes were located on the chromosome and 1657 genes were located in the megaplasmid. SY1 strain has 273 unique genes compared with five representative R. solanacearum strains, and these genes were enriched in the plant-pathogen interaction pathway. SY1 possessed a higher syntenic relationship with phylotype I strains, and the arsenal of type III effectors predicted in SY1 were also more closely related to those of phylotype I strains. SY1 contained 14 and 5 genomic islands in its chromosome and megaplasmid, respectively, and two prophage sequences in its chromosome. In addition, 215 and 130 genes were annotated as carbohydrate-active enzymes and antibiotic resistance genes, respectively. CONCLUSION: This is the first genome-scale assembly and annotation for R. solanacearum which isolated from infected P. cablin plants. The arsenal of virulence and antibiotic resistance may as the determinants in SY1 for infection of P. cablin plants.

Biphenyl metabolites from the patchouli endophytic fungus Alternaria sp. PfuH1.

Patchouli is a tropical medicinal and spice crop with high economic value, and the endophytic microorganism is also one of its important components and can provide new active compounds with medicinal use. In the present study, four new biphenyl compounds named 3-O-demethylaltenuisol (1), (-)-dialtenuisol (5) and (+)-dialtenuisol (6), and altertoxin VII (9), as well as six known related compounds, were isolated from the patchouli (Pogostemon cablin) endophytic fungus Alternaria sp. PfuH1. The structures of the new compounds were elucidated from spectroscopic data, ECD spectra analysis, and ECD calculations. Compounds 5 and 6 are a pair of dimeric axially chiral enantiomers. Compounds 2, 4, and 9 showed antibacterial activities against S. agalactiae with MIC values of 9.3, 85.3, and 17.3 µg/mL, respectively, and compound 4 also showed weak antibacterial activity against E. coli with MIC value of 128 µg/mL.

Cytotoxic triquinane-type sesquiterpenoids from the endophytic fungus Cerrena sp. A593.

The culture broth of Cerrena sp. A593, which was isolated from Pogostemon cablin, showed potent cytotoxicity against several human tumor cell lines. The following chemical study resulted in the isolation of two new triquinane-type sesquiterpenoids, named cerrenins D (1) and E (2), along with two known compounds plerocybellone A (3) and chloriolin B (4). Their structures were fully assigned with the aid of extensive spectroscopic analysis (1H and 13C NMR, HSQC, HMBC, 1H-1H COSY, HRESIMS, and IR) and data from the literature. Moreover, cytotoxic activity in vitro of compounds 1-4 were evaluated against SF-268, MCF-7, NCI-H460, and HepG-2 tumor cell lines. The new compound 1 exhibited weak growth inhibitory activity against all the four tumor cell lines with IC50 values of 41.01, 14.43, 29.67, 44.32 µM.

[Construction of Tn5 transposon insertion mutants of Ralstonia solanacearum isolated from Pogostemon cablin].

Ralstonia solanacearum strain PRS-84 used in this study was isolated from diseased Pogostemon cablin plants in our previous study.The competent cells of R.solanacearum strain PRS-84 were transformed by electroporation with Tn5 transposon and then were plated on TTC agar plates containing kanamycin to select for kanamycin-resistant colonies.The detection of kanamycin-resistant gene in kanamycin-resistant colonies was performed by PCR.Further,the flanking fragments of Tn5 transposon insertion site in the mutants were amplified by inverse PCR,and the flanking fragments were sequenced and analyzed.The results indicated that the kanamycin-resistant colonies were obtained in the transformation experiment of R.solanacearum strain PRS-84 by electroporation with Tn5 transposon.A specific band of approximately 700 bp was amplified by PCR from kanamycin-resistant colonies.The flanking sequences of Tn5 transposon insertion site in the transformants were obtained by inverse PCR.After sequencing and sequence analysis of Tn5 transposon insertion site in mutants,we preliminarily speculated that the Tn5 transposon inserted in the typ A gene,rec O gene and gid A gene in three mutants,respectively.A random mutagenesis system of R.solanacearum strain PRS-84 by electroporation with Tn5 transposon has been established,and the Tn5 insertion mutants have been obtained.This study might facilitate the creation of mutant library and the discovery of the virulence gene of R.solanacearum isolated from P.cablin.

Two new metabolites from Daldinia eschscholtzii, an endophytic fungus derived from Pogostemon cablin.

The chemical investigation of the mycelia of endophytic fungus Daldinia eschscholtzii A630, which was isolated from the medicinal plant Pogostemon cablin, resulted in the isolation of two new compounds, named eschscholin A (1), 3-ene-2-methyl-2H-1-benzopyran-5-ol (2), and one new natural product 3,5-dihydroxy-2-methyl-4H-chromen-4-one (3), along with seven known compounds. Their structures were fully characterized by means of detailed spectroscopic analysis, and in comparison with published data for known compounds. All of the isolated compounds (1-10) were evaluated for their antibacterial activities.

A practical random mutagenesis system for Ralstonia solanacearum strains causing bacterial wilt of Pogostemon cablin using Tn5 transposon.

A practical random mutagenesis system of Ralstonia solanacearum by electroporation with Tn5 transposon was established, which may be utilized to provide genetic approach to study virulence genes of R. solanacearum strains and create nonpathogenic mutants for biological control of bacterial wilt in Pogostemon cablin. R. solanacearum strain PRS-84 used in this study was isolated from P. cablin plants infected with bacterial wilt. The bacterial suspension of R. solanacearum strain PRS-84 was mixed with Tn5 transposome complex and the mixture was transformed by electroporation. The electroporated cells were then spread on the 2, 3, 5-triphenyltetrazolium chloride agar plates containing kanamycin to select the kanamycin-resistant colonies. Several factors which determined the bacterial transformation efficiency were optimized. The transformation process was shown to be optimal at the electric field strength of 12.5 kV cm-1. Bacterial cells harvested at mid-exponential phase gave the highest transformation efficiency. 10 µg mL-1 kanamycin was found to be the optimal concentration for transformant selection. Tn5 insertion mutants of R. solanacearum strain PRS-84 were identified by PCR amplification and Southern blot analysis. Mutants subcultured for 100 passages were also detected by PCR amplification and Southern blot analysis. Furthermore, pathogenicity screening test of mutants was performed by inoculating in vitro regenerated patchouli plants. Results revealed that mutants with a single Tn5 insertion in their genomes were obtained from R. solanacearum strain PRS-84, and the Tn5 insertion could be stably inherited in the mutants. Then, mutants with reduced pathogenicity were selected.

[Sesquiterpenoids of endophytic fungus Cerrena sp. from Pogostemon cablin and their cytotoxic activities].

The secondary metabolites of endophytic fungus Cerrena sp.A593 from Pogostemon cablin and their cytotoxic activities were investigated. Eight sesquiterpenoids were isolated from the fermentation broth of the strain A593 by silica gel, reverse phase silica gel, Sephadex LH-20, HPLC and so on. Their structures were identified as chloriolin B(1), chloriolin C(2), pleurocybellone A(3), dihydrohypnophilin(4), cucumin F(5), antrodin A(6), 10α-hydroxyamorphan-4-en-3-one(7), and connatusin A(8). Compounds 1- 8 were firstly found from the genus Cerrena. All isolated sesquiterpenoids were evaluated for in vitro cytotoxic activities against HepG-2, SF-268, MCF-7 and NCI-H460 tumor cell lines. Compounds 1-3 showed inhibitory activities against the four tumor cell lines with IC50 values ranging from 20.33 to 63.13 µmol•L⁻¹.

[Study on communities of endophytic fungi from Pogostemon cablin and their antimicrobial activities].

Seventy-two strains of endophytic fungi were isolated from roots, stems and leaves of Pogostemon cablin and identified as 40 species of 25 genera based on ITS sequences analysis. Among them, Phomopsis, Colletotrichum and Fusarium were dominant genera. Distribution of endophytic fungi in P. cablin showed obvious tissue-specificity, and more strains were isolated from stems with an isolation rate of 78%. The bioassay results indicated that 34 strains of 15 genera displayed antimicrobial activities against at least one of test bacteria or plant pathogenic fungi. The results obtained in this study showed that endophytic fungi in P. cablin were rich in species diversity, and some strains exhibited strong antimicrobial activities, which deserve further research.

Induction of defense-related enzymes in patchouli inoculated with virulent Ralstonia solanacearum

Background: Defense-related anti-oxidative response is a vital defense mechanism of plants against pathogen invasion. Ralstonia solanacearum is an important phytopathogen. Bacterial wilt caused by R. solanacearum is the most destructive disease and causes severe losses in patchouli, an important aromatic and medicinal plant in Southeast Asia. The present study evaluated the defense response of patchouli inoculated with virulent R. solanacearum. Results: Results showed that the basic enzymatic activities differed not only between the leaves and stems but also between the upper and lower parts of the same organ of patchouli. POD, SOD, PPO, and PAL enzymatic activities were significantly elevated in leaves and stems from patchouli inoculated with R. solanacearum compared to those in control. The variation magnitude and rate of POD, PPO, and PAL activities were more obvious than those of SOD in patchouli inoculated with R. solanacearum. PAGE isoenzymatic analysis showed that there were one new POD band and two new SOD bands elicited, and at least two isoformic POD bands and two SOD bands were observably intensified compared to the corresponding control. Conclusion: Our results suggest that not only defense-related enzymatic activities were elevated but also the new isoenzymatic isoforms were induced in patchouli inoculated with R. solanacearum.

Two Trichothecene Mycotoxins from Myrothecium roridum Induce Apoptosis of HepG-2 Cells via Caspase Activation and Disruption of Mitochondrial Membrane Potential.

Trichothecene mycotoxins are a type of sesquiterpenoid produced by various kinds of plantpathogenic fungi. In this study, two trichothecene toxins, namely, a novel cytotoxic epiroridin acid and a known trichothecene, mytoxin B, were isolated from the endophytic fungus Myrothecium roridum derived from the medicinal plant Pogostemon cablin. The two trichothecene mytoxins were confirmed to induce the apoptosis of HepG-2 cells by cytomorphology inspection, DNA fragmentation detection, and flow cytometry assay. The cytotoxic mechanisms of the two mycotoxins were investigated by quantitative real time polymerase chain reaction, western blot, and detection of mitochondrial membrane potential. The results showed that the two trichothecene mycotoxins induced the apoptosis of cancer cell HepG-2 via activation of caspase-9 and caspase-3, up-regulation of bax gene expression, down-regulation of bcl-2 gene expression, and disruption of the mitochondrial membrane potential of the HepG-2 cell. This study is the first to report on the cytotoxic mechanism of trichothecene mycotoxins from M. roridum. This study provides new clues for the development of attenuated trichothecene toxins in future treatment of liver cancer.

[Study on cytotoxic secondary metabolites of endophytic fungus Diaporthe longicolla A616 from Pogostemon cablin].

To study active secondary metabolites of endophytic fungus Diaporthe longicolla A616 isolated from Pogostemon cablin. Ten compounds were isolated from fermentation product of the strain 616 by silica gel, reverse phase silica gel, Sephadex-LH20, HPLC and so on. Their structures were identified as 1,3-diamino-1,3-dimethylurea(1),(7R,9R)-7-hydroxy-9-propyl-5-nonen-9-olide(2), Ergosta-5,7,22-trien-3ß-ol(3),(22E,24R)-ergosta-4,6,8(14)-22-tetraen-3-one(4),(22E,24R)-3ß,5α-dihydroxy-6ß-ergosta-7,22-diene(5), citreoisocoumarin(6), glycerol monolinoleate(7), 1-(2-hydroxyethoxy)ethyl(E)-octadec-9-enoate(8), cyclo-(L-Pro-L-Ala)(9), cyclo(L)-Pro-(L)-Val(10), respectively, based on extensive spectroscopic analysis and literature comparisons. Compounds 6-10 were isolated from the genus Diaporthe for the first time. All isolated compounds were evaluated for in vitro cytotoxic activities against SF-268, MCF-7, NCI-H460 and HepG-2 tumor cell lines. Compounds 4 and 5 showed potent growth inhibitory activities against the four cell lines with IC50 values of 5.3, 6.5, 12.2, 6.1µmol•L⁻¹ and 8.2, 5.2, 6.1, 9.4µmol•L⁻¹, respectively.