Effects of mycorrhizal-associated streptomycetes on growth of Laccaria bicolor, Cenococcum geophilum, and Armillaria species and on gene expression in Laccaria bicolor

Coplate assays were conducted to determine effects of two mycorrhizal-associated Streptomyces species, strains A and H, on growth of the ectomycorrhizal fungi Laccaria bicolor and Cenococcum geophilum, and on the pathogenic fungi Armillaria ostoyae and ii. gallica. Strain A stimulated growth of the ectomycorrhizal fungi, but inhibited growth of the Armillaria species. Strain H inhibited growth of all fungi. The effects of the streptomycetes on L. bicolor gene expression were also examined. For this, the fungus was grown in Roux bottles containing culture filtrates at 50% concentration from strains A or H. At 24, 48, and 72 h, the fungus was harvested, mRNA was isolated, and in vitro translation protein products were analyzed by gel electrophoresis. Noticeable differences were seen in protein profiles among the treatments and the control. New protein bands were observed when the fungus was exposed to filtrate from strain A compared to the untreated control. In contrast, filtrate from strain H tended to suppress fungal gene expression as evidenced by the disappearance of protein bands. The use of streptomycetes for enhancement of mycorrhizal formation and improvement of plant growth is discussed.