Thus, general inhibitors of fungi and/or bacteria, selective inhibitors, and a selective fungal growth-promoting strain were chosen. HPLC analyses revealed great differences in substance production. For example, strains 29 and 30 exhibited comparable impacts on fungal growth, yet they differed greatly in the numbers of detected products

(10 vs. 2). The strain producing the most unreported metabolites, AcM29, was characterized by a complex Streptomyces-fungus interaction spectrum. AcM29 had a negative impact on A. muscaria, H. cylindrosporum and L. bicolor but did not inhibit plant pathogenic fungi. Streptomycetes and other tested Gram-positive bacteria were inhibited by AcM29, while Gram-negative bacteria were only slightly influenced. This suggests that in search for Streptomyces

strains producing putatively novel compounds, a preliminary selleckchem screen should not only target fungi and Gram-negative bacteria, but also the streptomycetes. Heterobasidion infects roots in particular by growing over root to root contacts [31], and the roots of their host trees are predominatly mycorrhizal [12]. Ro 61-8048 price cycloheximide producing streptomycetes on the mycorrhizal roots could thus potentially affect root rot development. We observed that the addition of 1 nmol cycloheximide to the culture medium mimicked the impact of cycloheximide producer AcM11 to Heterobasidion PSI-7977 concentration species. Neither of the other compounds produced by AcM11 (antibiotic Acta 2930 B1, actiphenol and ferulic acid) affected the growth of H. abietinum

or H. annosum, Rolziracetam indicating that cycloheximide is responsible for the observed growth inhibition by AcM11. The role of cycloheximide in the inhibition of Heterobasidion species is supported by our study with another cycloheximide producing streptomycete, Streptomyces sp. A230 from South Brazilian soil. Whereas H. abietinum is killed by A230, H. annosum still retains 30% of its growth rate. Interestingly, A230 not only produces cycloheximide, but also actiphenol, a combination also observed in AcM11 (S.D.S, N.H., A. Zander and L. Braun, unpublished). H. abietinum and H. annosum have been reported to be physiologically and taxonomically distinct species [31]. The data of Lehr et al. [21] indicate that the two species also respond differently to cycloheximide: the levels of gene expression by H. abietinum and H. annosum are highly distinct upon cycloheximide application. Long-term screening of streptomycetes shows that approximately 10% of Streptomyces isolated from soil produce cycloheximide (H.-P. Fiedler, unpublished). It would thus be expected that most fungi have developed resistance or at least tolerance against the antibiotic, since they supposedly regularly encounter cycloheximide producers in the rhizosphere. P. croceum and H.