Evidence that the fungus cultured by leaf‐cutting ants does not metabolize cellulose

Abstract

Leaf-cutting ants are a very specialized group of ants that cultivate fungus gardens in their nests, from which they obtain food. The current opinion is that the fungus cultivated by leaf-cutting ants digests cellulose. Here we reassess the cellulose-degrading capability of the fungus by using two complementary approaches tested in four Attini species (genera Atta and Acromyrmex): (1) ability of fungus to grow in cellulose; and (2) lignin/cellulose ratio in the refuse material dumped outside the nest, as an indicator of cellulose consumption. We found that (1) the fungus did not grow in cellulose, and (2) the lignin/cellulose ratio was much lower in the ants' refuse than in material digested by cellulose-digesting organisms, such as brown-rot fungus, termites, and ruminant mammals. This evidence strongly suggests the inability of the fungus to degrade cellulose. Therefore, the fungus-ant symbiosis and the ecological role of leaf-cutting ants need to be reconsidered.

Ant-fungal species combinations engineer physiological activity of fungus gardens

“…One of the more surprising findings of this study sustains an ongoing debate on whether Attamyces can metabolize cellulose. A number of studies report significant cellulase activity for Attacultivated fungi grown on a variety of natural and artificial diets (Bacci et al, 1995;D'Ettorre et al, 2002;Martin and Weber, 1969;Schiøtt et al, 2008;Silva et al, 2003), whereas other studies failed to find significant cellulase activity (Abril and Bucher, 2002;Bucher et al, 2004). The results presented here are intriguing because they suggest that T. arizonensis colonies growing Attamyces on natural substrates (catkins) can in fact metabolize cellulose because Attamyces grown by T. arizonensis exhibited higher cellulase activity than Attamyces grown by A. texana.…”

Metagenomic and metaproteomic insights into bacterial communities in leaf-cutter ant fungus gardens

“…For over a hundred years after Belt's Bacterial communities in ant fungus gardens FO Aylward et al pioneering discovery it was believed that the fungus gardens of leaf-cutter ants represented a monoculture of the fungal cultivar that degraded plant cellwall material and converted it into nutrients for the ants (Weber, 1966;Martin and Weber, 1969). However, both the lignocellulolytic capacity of the cultivar and the view that fungus gardens are composed solely of the fungal mutualist have been recently challenged (Gomes De Siqueira et al, 1998;Abril and Bucher, 2002;Scott et al, 2010;Suen et al, 2010). In this study, we explored the hypothesis that bacteria are common constituents of fungus gardens that could be participating in plant biomass degradation and nutrient cycling.…”

“…Originally it was thought that the fungal cultivar primarily degraded cellulose, and that this was the main polymer converted into nutrients for the ants (Martin and Weber, 1969). However, the cellulolytic capacity of this fungus has come into question, as it has been shown that pure cultures cannot grow on cellulose as a sole carbon source (Abril and Bucher, 2002). This has led to the suggestion that cellulose is not deconstructed in leaf-cutter ant fungus gardens, but rather that the fungal cultivar uses a variety of hemicellulases to deconstruct primarily starch, xylan and other plant polymers (Gomes De Siqueira et al, 1998;Silva et al, 2006a, b;Schiott et al, 2008).…”

Convergent coevolution in the domestication of coral mushrooms by fungus–growing ants

“…Therefore, encounters between the ancestral pterulaceouscultivating ant species and Pterulaceae species would be probable. The rare use of wood to grow lepiotaceous cultivars is consistent with the non-wood substrates of the freeliving relatives of the lepiotaceous cultivars and the poor ability of the lepiotaceous cultivars to degrade cellulose (Gomes de Siqueira et al 1998;Abril & Bucher 2002). Although the enzymatic potential for wood decay by the pterulaceous cultivar has yet to be investigated, a closely related species, Pterula echo, has been grown in axenic Figure 2.…”