Suppression of aerial hyphae by staling products of Postia placenta

Abstract

Isolate ME20 is a wild-type monokaryotic strain of the brown-rot fungus Postia placenta that does not cause significant weight losses in standard soilwood block decay tests. It also fails to form aerial hyphae in liquid and agar culture. This abnormal morphological feature may be caused by the same aberrant physiology that prevents the strain from efficiently degrading wood. Aerial hyphae formation was suppressed in MAD698, a standard floccose strain of P. placenta, when spent media from 14-day-old ME20 cultures made up 40% or more of the nutrient medium. Spent media from MAD698 cultures caused a similar effect but only at 80% and 100% concentrations. This suppression does not appear to be caused by nutrient deprivation or by the activity of extracellular autolytic enzymes. The suppressive factor has a molecular weight of <10 000 Da, is resistant to boiling, and thus probably non-enzymatic. The inhibition of aerial hyphae formation is probably due to unidentified, low molecular weight staling products.