| Two ectomycorrhizoplane-associated Streptomyces species, designated as strains A and H, were studied for their effects on the growth and gene expression of ectomycorrhizal fungi. Using co-culture studies, Strain A showed slight stimulation of all fungi, while strain H strongly inhibited the ectomycorrhizal fungi Laccaria fraterna and L. bicolor. Cenococcum geophilum was inhibited to a lesser extent.Strain H demonstrated inhibition when co-cultured with gram-positive bacteria and most filamentous fungi (saprophytic, pathogenic, wood-decay, and mycorrhizal). Most yeasts and dimorphic molds and all gram-negative bacteria were not inhibited. To test the effects of the products excreted by Streptomyces species on L. bicolor gene expression, fungal mRNA was isolated after exposure to strains A and H filtrates and translated in vitro. New, labelled protein bands were observed in the strain A treatments compared to the control in general, strain H treatments suppressed fungal gene expression.To assess the nutritional conditions necessary for production of the inhibitors, different nitrogen and carbon sources were added to a chemically defined medium. Growth of strain H on glycerol/NHThe dark brown and red pigments and the inhibitory compounds produced by strain H were also characterized. The brown pigment contained a mixture of blue, green, and purple chromophores. Analysis of the blue pigment indicated it to be an indole-like compound. A red pigment was also produced by strain H which showed a strong correlation with the inhibitory effect. Tests to determine if the pigments could be melanin or an ochronotic pigment were negative. The inhibitory compound(s) could be extracted into chloroform. Thin layer chromatography and bioautography demonstrated the inhibitory compound(s) possess both non-polar and polar properties.Overall, Streptomyces strain A shows promise for use as dual inoculation with the ectomycorrhizal fungi for red pine seedlings. Strain H does not appear to be compatible with the beneficial ectomycorrhizal fungi however, it may be useful as a biological control agent in the field. |
