Isolation and characterization of Streptomyces strains antagonistic to phytopathogenic fungi and analysis of antibiotics potentially involved in disease control.

摘要

Streptomyces are an important group of microorganisms that live on decaying organic matter in soil. This group produces valuable secondary metabolites that may be useful for control of fungal plant diseases and/or lignin degradation. This dissertation examines the fungal disease control capabilities and the lignocellulolytic activity of members of this group. One strain, Streptomyces lydicus WYEC 108 controls damping-off diseases caused by Pythium sp. To identify possible mechanisms responsible for disease control, metabolites active against Pythium ultimum and Saccharomyces cerevisiae were isolated and characterized. The antifungal metabolites were extracted from the culture broth with 2-propanol/ethyl acetate and from freeze-dried broth with methanol. Two antifungal metabolites were separated by solvent partitioning, florisil clean up, flash chromatography and preparative thin layer chromatography. An analyte active against yeast, but inactive against Pythium, was purified to 70% purity and determined was by electrospray ionization mass spectrometry to have a mass of 353 amu and had aminocyclitol antibiotic characteristics. The identity of the second analyte, active against Pythium, was not determined. In an effort to identify new fungi-inhibiting organisms that degrade thatch and suppress fungal diseases of turf, approximately 290 additional putative Streptomyces strains were isolated from soil and compost and screened for inhibitory activity to phytopathogenic fungi. Of the isolates tested, 47% were inhibitory to Pythium ultimum, 46% to Rhizoctonia solani, 61% to Fusarium oxysporum , and 52% were inhibitory to Gaeumannomyces tritici var. tritici. Some of these isolates were grown on corn lignocellulose in solid substrate flask cultures for 3 weeks during which lignocellulose weight losses ranged from 0 to 24%. Analysis of the Klason lignin and carbohydrate content of the residual lignocellulose indicated the isolates grew primarily at the expense of the carbohydrate with little degradation of the lignin. The strongly lignocellulolytic, fungi-inhibiting isolates should be useful for degrading thatch and for protecting turf from fungal diseases.