The Irreversible Loss of a Decomposition Pathway Marks the Single Origin of an Ectomycorrhizal Symbiosis
Figure 4
Experimental demonstration of the loss of cellulolytic saprotrophic capabilities by ectomycorrhizal Amanita species.
Fourteen species, including saprotrophic and ectomycorrhizal Amanita and two saprotrophic Volvariella species, were grown on sterile grass litter to test for the use of litter as a sole carbon source. Enzyme activities of endoglucanase (E), cellobiohydrolase (C) and beta-glucosidase (ß) were also measured. The same species were grown on media with a protein (casein hydrolysate) as sole nitrogen source. Colony diameter as well as clearing of milk agar was measured to indicate growth on protein and protease activity, respectively. Values of cellulolytic and proteolytic growth and activity are expressed as relative to the maximum value (from 0 to 1) for each parameter across the species. The difference in growth between ectomycorrhizal and saprotrophic species on litter is highly significant, according to phylogenetically independent contrasts (F1,11 = 7.84, p = 0.017). Contrasts for all other data were not significant.