Sipeimine-Producing Endophytic Fungus Isolated from Fritillaria Ussuriensis Hong Yin* and Juan-Li Chen
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Sipeimine-Producing Endophytic Fungus Isolated from Fritillaria ussuriensis Hong Yin* and Juan-Li Chen College of Life Science, Northwest University, Xi’an, 710069, China. Fax: 0086 2988 303572. E-mail: [email protected] * Author for correspondence and reprint requests Z. Naturforsch. 63 c, 789Ð793 (2008); received April 25/June 23, 2008 Ten strains of endophytic fungi were isolated from the bulbs of the traditional Chinese medicinal plant Fritillaria ussuriensis. The extract from one of them, Fu7, showed a positive reaction with Dragendorff’s reagent and the same Rf value in thin-layer chromatography (TLC) analysis as authentic sipeimine. A further TLC scan and high-performance liquid chromatography-evaporative light-scattering detection (HPLC-ELSD) showed that one in- gredient of the extract of strain Fu7 had a similar absorption curve in the range 200Ð700 nm and the same retention time as authentic sipeimine. Thus, the fungus produces the bioactive ingredient sipeimine, as does its host plant, and could be used for the production of sipeimine by fermentation. Key words: Endophytic Fungus, Fritillaria ussuriensis, Alkaloid Introduction (Stierle et al., 1993). Since then, continuing studies have reported that many endophytes Ð microor- Fritillaria ussuriensis Maxim. is a perennial plant ganisms that inhabit the tissues of living plants Ð of the family Liliaceae. The bulbs of the plant are produce a plethora of substances of potential use one of the traditional Chinese herbal medicines in modern medicine, agriculture, and industry (TCM). It has been used as one of the most impor- (Strobel and Daisy, 2003; Tan and Zou, 2001; Guo, tant antitussive and expectorant drugs in China 2001; Liu et al., 2005). and other Asian countries for thousands of years An endophytic fungus isolated from F. ussurien- (Li et al., 2001; Chen et al., 2006). It is now offi- sis, that produces the same bioactive compounds cially recorded in the National Pharmacopoeia of (alkaloids) as its host plant, would not only reduce China (Editorial Board of the Pharmacopoeia of the need to harvest the rare plant but would also the People’s Republic of China, 2005). The main preserve our ever-diminishing biodiversity. Fur- active constituents of the bulbs are steroidal alka- thermore, it is recognized that a microbial source loids, such as sipeimine, peimine, pingpeinine A of a valuable product is usually easier and more and B (Xu et al., 1982; Chen et al., 2006). economically produced, effectively reducing its The natural resource of this medicinal material is market price (Strobel and Daisy, 2003). now in short supply and becomes vulnerable be- Therefore, this study was undertaken to ascer- cause of the overcollection of the plant (State Envi- tain the presence of endophytic fungi in the plant ronmental Protection Administration of China and F. ussuriensis and to ascertain whether any such Institute of Botany, 2000). Although this plant has fungus produces Fritillaria alkaloids. In this way, been cultivated at several places in China, the con- we hoped to develop a new method of producing flict between supply and demand is an ongoing is- these plant-derived pharmaceutical components, sue, because its growth requirements in the environ- to resolve the conflict between natural resource ment are quite stringent and its growth rate is slow. protection and the requirement for TCM plants. Therefore, it is critical to find an alternative way to produce these alkaloids to satisfy the demand. Material and Methods In 1993, Stierle and his coworkers reported that Plant material an endophytic fungal strain isolated from Taxo- myces andreanae produces the bioactive com- Fresh bulbs of F. ussuriensis were collected from pounds taxol and taxane, as does its host plant the botanical garden of Northwest University, 0939Ð5075/2008/1100Ð0789 $ 06.00 ” 2008 Verlag der Zeitschrift für Naturforschung, Tübingen · http://www.znaturforsch.com · D 790 H. Yin and J.-L. Chen · Sipeimine Bioproduction Xi’an, China, where the plant was introduced from Samples extracted from the selected strain were the Institute of Special Products, Jilin, China. spotted onto a precoated silica-gel plate together with authentic sipeimine solution. The plate was Authentic drug developed in a preselected solvent system of ethyl Authentic sipeimine was purchased from the acetate/methanol (6:0.2, v/v). The plate was then Shaanxi Provincial Institute for Drug Control, fixed in a drying oven at 105 ∞C for about 1 h and Xi’an, China. the sample components visualized by spraying the plate with improved Dragendorff’s reagent. Isolation of endophytic fungi The relative front (Rf) values and the colour of the spots were measured and compared. The tar- The endophytic fungal strains were isolated by get strain was identified according to the results. routine microbiological methods from the fresh bulbs of F. ussuriensis. The purified strains were Distribution of sipeimine inside numbered and stored in a refrigerator at 4 ∞C for and outside the mycelia later use. To increase the culture scale of the target strain Determination of growth curves selected from the TLC reselection, the mycelia The mycelial suspension of each strain was inocu- and culture filtrate samples were treated sepa- rately according to the protocol showed in Fig. 1, lated in equal amount into Erlenmeyer flasks con- Ț taining potato-sucrose liquid medium. The cul- but the compounds were not mixed at step 7 . tures were then incubated at 25 ∞Cona Both samples were analyzed individually by TLC reciprocal shaker. according to the procedure described above, to de- Three flasks of each strain culture were har- termine the distribution of the Fritillaria alkaloids vested every day by filtration, then the mycelia inside and outside the mycelia. were oven-dried and the average dry weights were used to draw a growth curve for each strain. Both Product identification the mycelia and their culture filtrates were pre- TLC scan served for analysis. The extracts of the strains selected with strain reselection and the sipeimine standard were ap- Qualitative examination of alkaloids Ð plied to a silica-gel plate for TLC analysis and Dragendorff’s reaction visualized by the colour reaction produced with The alkaloids in dried mycelia and culture fil- Dragendorff’s reagent. The TLC plate was then trates were extracted using ethanol and chloro- scanned with CAMAG TLC Scanner 3 (CAMAG, form. Both the extracts from the mycelia and from Muttenz, Switzerland) in the wavelength range the culture filtrates were dried by decompression 200Ð700 nm. evaporation, then redissolved in water, and acidi- fied with dilute HCl. Improved Dragendorff’s re- High-performance liquid chromatography-evapo- agent was added to each sample and the changes rative light-scattering detection (HPLC-ELSD) of the colour and the formation of deposits were Standard solution: 0.05 mg/L sipeimine in metha- observed. An orange colour or deposit constituted nol. Instrument and operation conditions: HPLC a positive result (Shanghai Institute of Materia chromatograph, Agilent 1100 system (Agilent Medica, 1972). Technologies, Santa Clara, California, USA); con- trol system, N2000 chromatography station (Zheji- Strain reselection Ð thin layer chromatography ang University, PRC); chromatographic column, (TLC) Agilent ZORBAX SB-C18 (150 mm ¥ 4.6 mm, The strain that reacted positively with Dragen- 5 μm); column temperature, 30 ∞C; mobile phase, dorff’s reagent was cultured in potato-sucrose acetonitrile/water (71:29, v/v) containing 0.03% liquid medium for a suitable time based on its diethylamine at a flow rate of 0.8 mL/min; sample growth curve and the primary qualitative results injection volume, 20 μL; ELSD detector, Alltech obtained with Dragendorff’s reagent. The product 2000 (Alltech, Deerfield, Illinois, USA); gasify- was extracted according to the preselected proto- ing temperature, 85 ∞C; flow rate of nitrogen gas, col shown in Fig. 1. 2.1 L/min. H. Yin and J.-L. Chen · Sipeimine Bioproduction 791 Fig. 1. Protocol for the extraction of cultures. Results and Discussion consistent with the general opinion that secondary Growth curves of the isolated strains metabolites are often produced after growth has stopped (Griffin, 1994). Ten endophytic fungal strains (Fu1ÐFu10) were isolated from the bulbs of F. ussuriensis confirming the proposition that endophytic microorganisms Reselection of the sipeimine-producing strain can be found in virtually every plant (Strobel and According to TLC detection, only the sample Daisy, 2003). from strain Fu7 produced a spot with the same Rf The results of the reaction with improved Dra- value as authentic sipeimine. So, it was selected gendorff’s reagent indicated that both the mycelia for further analysis. and the culture filtrates from strains Fu4, Fu6, Fu7, Fu8, and Fu10 contained alkaloids or similar Distribution of sipeimine inside compound(s). Therefore, they were selected for a and outside the hyphae further TLC assay. From their growth curves (Figs. 2a and b) it can be seen that these alkaloids were Further TLC analysis showed that the sample all produced around the stationary phase, which is from the Fu7 culture filtrate produced four spots, 792 H. Yin and J.-L. Chen · Sipeimine Bioproduction (a) host plant F. ussuriensis. The main product was present in the culture filtrate. Therefore, sub- sequent assays were mainly performed using the culture filtrate. Product identification TLC scan From Fig. 3 it can be seen that the Fu7 extract has a similar absorption curve to that of a standard (b) sipeimine solution. Thus, the Fu7 extract should have the same chromophores as sipeimine. HPLC-ELSD analysis The HPLC-ELSD chromatograms show that both the sample and authentic sipeimine have the same retention times of about 10 min. Therefore, we infer that the sample contains the bioactive compound sipeimine. Fig. 2. Growth curves of the strains (a) Fu1ÐFu5 and (b) Most Fritillaria alkaloids are nonchromophoric, Fu6ÐFu10. which makes the use of direct UV detection with- out pre- or post-column derivatization impossible.