BIOLOGICALLY ACTIVE SECONDARY METABOLITES FROM ENDOPHYTIC FUNGI
B SCHULZ1 and K KROHN2
1Institut fur Mikrobiologie, Technische Universitat Braunschweig, Spiehnannstrasse 7, D-38106 Braunschweig, Germany; 2Fachbereich Chemie und Chemietechnik der Universitat-GH-Paderbom, Warburger Strasse 100, D-33098 Paderbom, Germany
Background and objectives
Results and conclusions
In order to obtain a maximum proportion of novel secondary metabolites, the following criteria were applied for the choice of the fungal strains and their cultivation for the isolation of the active substances. (1) Although not suitable for industrial throughput screening, culture was on semi-solid agar media at room temperature, where fungi produce more metabolites than in liquid culture. (2) The taxa of the fungal isolates were, if possible, determined; these were compared with entries in a data bank of secondary metabolites to exclude redundant discoveries of compounds. (3) The metabolic profile of the fungal culture extract as revealed by thin-layer chromatography (TLC) yielded either a large number and /or high concentrations of the substances. Bioassays of the TLCs revealed herbicidal or fungicidal metabolites.
As a group, the endophytes yielded the highest proportion of novel structures: 50% of the structures determined from the endophytic culture extracts were new compared with only 33% of those from cultures of soil isolates. In addition, 95% of the metabolites isolated from endophytic cultures were herbicidally active. Not only do these results show that endophytes are a good source of biologically active novel compounds, but they also suggest that they are synthesized in situ. Possible roles that these metabolites might play in vivo are: (1) a weakening of the host tissue and/or defense to better enable infection, (2) an increase in the membrane permeability of the host, permitting a better nutrient supply for the endophyte, (3) in a senescent or weakened host, degradation of host tissue allowing the endophyte to grow as a nectrotroph.