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Microbiology. 2017 Nov;163(11):1578-1589. doi: 10.1099/mic.0.000546. Epub 2017 Oct 16.

Ultrastructural and microbial analyses of cellulose degradation in leaf-cutter ant colonies.

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Centro de Investigación en Estructuras Microscópicas, Universidad de Costa Rica, San José, Costa Rica.
Centro de Investigación en Enfermedades Tropicales, Universidad de Costa Rica, San José, Costa Rica.
Great Lakes Bioenergy Research Center, Wisconsin, USA.
Department of Bacteriology, University of Wisconsin-Madison, Wisconsin, USA.
Departamento de Bioquímica, Facultad de Medicina, Universidad de Costa Rica, Costa Rica.
Centro de Investigación en Biología Celular y Molecular, Universidad de Costa Rica, San José, Costa Rica.


Leaf-cutter ants (Atta and Acromyrmex) use fresh leaves to cultivate a mutualistic fungus (Leucoagaricus gongylophorus) for food in underground gardens. A new ant queen propagates the cultivar by taking a small fragment of fungus from her parent colony on her nuptial flight and uses it to begin her own colony. Recent research has shown that the ants' fungus gardens are colonized by symbiotic bacteria that perform important functions related to nitrogen fixation and have been implicated in contributing to plant biomass degradation. Here, we combine bacterial culturing in several media for counts and identification using the 16S rRNA gene with electron microscopy to investigate the process of cellulose degradation in the fungus garden and refuse dumps, and to assess the potential role of symbiotic bacteria. We show through electron microscopy that plant cell walls are visibly degraded in the bottom section of fungus gardens and refuse dumps, and that bacteria are more abundant in these sections. We also consistently isolated cellulolytic bacteria from all sections of fungus gardens. Finally, we show by culture-dependent and electron microscopy analysis that the fungus garden pellets carried by recently mated queens are colonized by fungus garden-associated bacteria. Taken together, our results indicate that cellulose is degraded in fungus gardens, and that fungus garden bacteria that may contribute to this deconstruction are vertically transmitted by new queens.


Atta; Leucoagaricus; cellulolytic bacteria; nuptial flight; symbiosis

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