Rapid shifts in Atta cephalotes fungus-garden enzyme activity after a change in fungal substrate (Attini, Formicidae)

Abstract

Fungus gardens of the basidiomycete Leucocoprinus gongylophorus sustain large colonies of leaf-cutting ants by degrading the plant material collected by the ants. Recent studies have shown that enzyme activity in these gardens is primarily targeted toward starch, proteins and the pectin matrix associated with cell walls, rather than toward structural cell wall components such as cellulose and hemicelluloses. Substrate constituents are also known to be sequentially degraded in different sections of the fungus garden. To test the plasticity in the extracellular expression of fungus-garden enzymes, we measured the changes in enzyme activity after a controlled shift in fungal substrate offered to six laboratory colonies of Atta cephalotes. An ant diet consisting exclusively of grains of parboiled rice rapidly increased the activity of endo-proteinases and some of the pectinases attacking the backbone structure of pectin molecules, relative to a pure diet of bramble leaves, and this happened predominantly in the most recently established top sections of fungus gardens. However, fungus-garden amylase activity did not significantly increase despite the substantial increase in starch availability from the rice diet, relative to the leaf diet controls. Enzyme activity in the older, bottom sections of fungus gardens decreased, indicating a faster processing of the rice substrate compared to the leaf diet. These results suggest that leaf-cutting ant fungus gardens can rapidly adjust enzyme activity to provide a better match with substrate availability and that excess starch that is not protected by cell walls may be digested by the ants rather than by the fungus-garden symbiont.

Differences in Forage-Acquisition and Fungal Enzyme Activity Contribute to Niche Segregation in Panamanian Leaf-Cutting Ants

“…Other recent studies have emphasized that the expression of enzymes can be remarkably plastic and substrate dependent [21], [34]. This is consistent with earlier notions that there are active feedback loops between forager supply and symbiont demand, such that foragers may discard some forage material under specific conditions where its excess processing would not be optimal [51].…”

Ant-fungal species combinations engineer physiological activity of fungus gardens

“…All T. arizonensis colonies were fed oak catkins (Quercus shumardii) ad libitum throughout the duration of the entire experiment. Colonies of the two species were fed the same type of catkins to avoid confounding the results with diet (Kooij et al, 2011).…”

“…bacterial biofilms) seems to be greater in the lower portions (Moller et al, 2011;Suen et al, 2010). Furthermore, because enzymatic activities in gardens depend on the substrates used by the ants (Kooij et al, 2011), all ant colonies of both species were fed a strict diet of oak catkins for 4 weeks prior to enzymatic assays. Finally, gardens were also sampled at least 48 h after the last feeding, so that there were no freshly deposited substrates in the gardens.…”

Disentangling nutritional pathways linking leafcutter ants and their co‐evolved fungal symbionts using stable isotopes

“…, Kooij et al. , Seal et al. ), and with the enzyme vectoring by ants to detoxify (De Fine Licht et al.…”

“…), nutritionally (Kooij et al. ), and biochemically (Howard ) diverse plant substrates, and when culitvars are farmed across ecological gradients (Mueller et al. ).…”