The thn (thin) mutant strain of Schizophyllum commune, which normally lacks aerial mycelium, produced excessive aerial hyphae when
surrounded by multiple wild-type (wt) colonies. When thn and wt mycelia were grown together, the radial growth rate of the thn
strain was increased, whereas the wt strain was clearly expressed in its growth, resulting in complete overgrowth of wt by thn
hyphae. Overgrowing even occurred when mixtures of fragmented hyphae of both strains with a hundred times excess of wt
hyphae over thn hyphae were grown from a single inoculum. Growth stimulation was also observed when thn and wt colonies were
separated by dialysis membrane (cut-off 6–8 kDa) suggesting that low molecular weight molecules may be involved. The observed
phenomena may explain the apparently very high frequency of occurrence of the recessive thn mutation in S. commune.