Endophytic Fungi From Rehamannia Glutinosa And Their Bioactive Metabolites

Microorganism is a bioresource of novel compounds with diverse activities,from microorganism we have isolated a lot of antibiotics with evident therapy. Duringthe past seven decades, thirty to fifty thousands natural products were found and morethan ten thousands of them showed various bioactivities and of which more than eightthousands were identified as anti-bacterial or anti-tumor agents. However, with thespread of drug-resisitence pathogenic microorganism, as well as the increase ofcancer, it has become a current emergency to explore new sources of active substance.More and more researches were made in this field and supply a lot of novel leadcompounds for screen of new antibiotics.Endophytes are microorganisms that live in the intercellular spaces of stems,petioles, roots and leaves of plants causing no discernible manifestation of theirpresence and have typically gone unnoticed . The symbiosis between plant andendophyte was ascertained, namely, the former protects and feeds the latter whichproduces'in return'bioactive (plant growth regulatory, antibacterial, antifungal,antiviral, insecticidal, etc.) substances to enhance the growth and competitiveness ofthe host in nature. Endophytes constitute a valuable source of bioactive secondarymetabolites and would be a source of new drugs of biotechnological importance andplant disease management programs.The following hypothesis was developed: both the pathogen-host and theendophyte-host interactions involve constant mutual antagonisms at least in partbased on the secondary metabolites the partners produce. Whereas the pathogen-hostinteraction is imbalanced and results in disease, that of the endophyte and its host is abalanced antagonism. In order to efficiently exploit its ecological niche, endophytesneeds to compete with other endophytes, pathogens and host, antibiotic metabolitesmay play important roles in the competitive process.Healthy wild Rehmannia glutinosa roots were collected in March 2007, Wushe county, Henan Province. 623 strains of endophytes were isolated from the plant,morphous and fingerprinting chromatography was used to delete the repeated strains.A total of 22 strains were isolated and only 4 of them were frequently appeared in theroot samples (isolation frequency>1%)and the strains were identified as Rhizoctoniasp.,Chaetomium sp.,Verticillium sp.,Mucor sp. Pyricularia oryzae P-2b were utilizedas pharmaco-model to screen the fungi with antifungal metabolites. The extracts fromthree endophytes displayed evident antibiotic activities against Pyricularia oryzaeP-2b.Significative results were abstracted according the researches: (1) diversity ofendophytes in the plant were approved and some endophytic fungi inhabited theplant relatively stable ; (2)different culture display diverse isolation frequencies, andmore different culture must be utilized to obtain more endophytic fungal withdifferent applicability. (3)mutual antagonism experiment approved that growth ofbiomass were evidently inhibited in the competitive process. (4) 12 compounds wereisolated from the fungi, structures of 9 compounds were elucidated. Three of thecompounds were elucidated to be new and were reported for the first time.Four fungal pathogens (Candida albicans, Cryptococcus neoformans,Trichophyton rubrum, Aspergillus fumigatus)were utilized to detect the anti-fungalactivities. Four compounds of them displayed inhibition against four fungal pathogensof different degree and two compouns displayed evident antagonism against severalhuman pathogens.