Antagonistic interactions between garden yeasts and microfungal garden pathogens of leaf-cutting ants

Abstract

We investigate the diversity of yeasts isolated in gardens of the leafcutter ant Atta texana. Repeated sampling of gardens from four nests over a 1-year time period showed that gardens contain a diverse assemblage of yeasts. The yeast community in gardens consisted mostly of yeasts associated with plants or soil, but community composition changed between sampling periods. In order to understand the potential disease-suppressing roles of the garden yeasts, we screened isolates for antagonistic effects against known microfungal garden contaminants. In vitro assays revealed that yeasts inhibited the mycelial growth of two strains of Escovopsis (a specialized attine garden parasite), Syncephalastrum racemosum (a fungus often growing in gardens of leafcutter lab nests), and the insect pathogen Beauveria bassiana. These garden yeasts add to the growing list of disease-suppressing microbes in attine nests that may contribute synergistically, together with actinomycetes and Burkholderia bacteria, to protect the gardens and the ants against diseases. Additionally, we suggest that garden immunity against problem fungi may therefore derive not only from the presence of disease-suppressing Pseudonocardia actinomycetes, but from an enrichment of multiple disease-suppressing microorganisms in the garden matrix.

Unraveling Trichoderma species in the attine ant environment: description of three new taxa

“…Several other studies with leaf-cutting ants (Atta and Acromyrmex) suggested that Trichoderma fungi are associated with the plant substrate foraged by workers (Barbosa 2004;Rodrigues et al 2008Rodrigues et al , 2009Rodrigues et al , 2011 Samuels et al 2006;Bae et al 2009;Chaverri et al 2011;Druzhinina et al 2012;Bailey and Melnick 2013). Regarding T. viride, this species was considered to be restricted to the north hemisphere and found in soil, trunks and decaying wood, with only two strains reported in the tropics, isolated as endophytes of Theobroma gileri (Ecuador) and Theobroma cacao (Brazil) (Lieckfeldt et al 1999;Jaklitsch et al 2006;Samuels et al 2006).…”

“…Since the first report of Trichoderma in colonies of leaf-cutting ants (Kreisel 1972), several studies reported the occurrence of this genus in colonies of these insects (Barbosa 2004;Poulsen and Currie 2006;Rodrigues et al 2008Rodrigues et al , 2009Augustin 2011;Rodrigues et al 2014). However, none of these studies used a detailed taxonomic approach to identify Trichoderma species that occur in this environment.…”

Bioprospecting of yeasts for amylase production in solid state fermentation and evaluation of the catalytic properties of enzymatic extracts

“…This region is generally used as the molecular marker for yeast identification (Kurtzman and Robnett, 1998;Schoch et al, 2012). PCR conditions were as follows: 96°C for 3 min, 35 cycles at 96°C for 30 s, 61°C for 45 s, and an extension step at 72°C for 1 min (Rodrigues et al, 2009). The expected size of amplicons (500-600 base pairs) were checked after electrophoresis in 1% agarose gel supplemented with GelRed ® (Biotium).…”

Ant-fungal species combinations engineer physiological activity of fungus gardens

“…This possibility was raised when T. septentrionalis and Trachymyrmex turrifex experienced fitness reductions after adopting Attamyces fungus (Seal and Mueller, 2014), which apparently was the result of invasion by weedy fungi destroying gardens, though the exact mechanism of garden decline was not known with certainty in that study. Trachymyrmex arizonensis likely associate with different microbial communities that are distinct from other species of Trachymyrmex, as do other attine species Rodrigues et al, 2011;Sen et al, 2009), which may or may not be able to withstand invasions by competitor fungi (Haeder et al, 2009;Mueller, 2012;Rodrigues et al, 2009). Another non-exclusive possibility is that ants may not apply the appropriate triggers to novel fungal symbionts that would stimulate the synthesis of the diverse enzymatic machinery required for the metabolism of carbohydrates, lignocelluloses and proteins that Attamyces is known to possess (Aylward et al, 2013).…”